VISUAL FACTORS RELATING TO IMAGE INTERPRETATION

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A000900040032-5
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 110
• Document Creation Date: December 28, 2016
• Document Release Date: October 27, 2004
• Sequence Number: 32
• Publication Date: June 30, 1966
• Content Type: REPORT

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FINAL REPORT NO. 226
June 30, 1966
VISUAL FACTORS RELATING TO IMAGE INTERPRETATION
Declass Review by NGA.
STAT
STAT
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FINAL REPORT NO. 226
June 30, 1966
VISUAL FACTORS RELATING TO IMAGE INTERPRETATION
kOPY N0. TAT
STAT
STAT
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Page
1.
INTRODUCTION
1
2.
GENERAL
3
2.1 Man-Machine Factors
6
2.1.1 Sensing
6
2.1.2 Processing
7
2.1.3 Actuating
9
2.1.4 The man-machine interface
10
2.1.4.1 Capabilities and limitations of man
and machine
10
2.1.4.2 Characteristics tending to favor humans
over machines
10
2.1.4.3 Characteristics tending to favor machines
over humans
14
3.
COLOR VISION
17
4.
FATIGUE
22
4.1 Sensory Deprivation
23
5.
STEREO VISION
25
APPENDIX A - SPIE SYMPOSIUM "THE HUMAN IN THE PHOTO OPTICAL SYSTEM"
ABSTRACTS AND COMMENTS
APPENDIX B - VISUAL PROCESSES - ANNOTATED BIBLIOGRAPHY
(with Table of Contents)
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1AT
SAT
STAT
This is the final report oniI Project No. 9277, "A Literature
Search of Visual Processes Relating to Photointerpretation." The objective
of this project has been to screen existing literature and research data on
vision and perception for significant factors applicable to the task of the
image interpreter. Ideally, these factors can then be utilized in design
considerations for interpretation equipment or working environment.
The encyclopedic nature of the topic under investigation has necessitated
a rather general approach in "feeling out" those specific subjects or sources
that appear most germane. During the course of the project, the sponsor's
program monitor has defined a number of specific topics of particular or
current interest to be investigated. Project reporting, to a large degree,
reflects these indicated fields of interest. Because of the broad and varied
implications of the overall subject of "vision research", and the admitted
difficulty of extrapolating purely experimental or isolated results to the
complex function of image interpretation, we would recommend that any future
effort of this nature concentrate on specific aspects of vision that can be
related to individual tasks of the image interpreter. A primary difficulty
of a shotgun-type investigation lies in the lack of a universally agreed-upon
definition of "image interpretation." Additionally, the various academic or
technical disciplines concerned with research on visual processes often take
widely differing or even conflicting approaches to the subject.
Principal investigator for the project initially was STAT
On her departure from became princi- STAT F pal investigator.
In April, 1966, attended the SPIE Symposium, "The
Human in the Photo-Optical System." Abstracts and comments on those papers
are presented in Appendix A.
Appendix B is an annotated bibliography of sources and abstracts,
arranged by subtopics. Much of the abstracted material presented is in the
form of working notes compiled during the investigations. As such, it
represents an attempt to grasp and become educated in the terminology and
theories of vision. It should not be regarded as a comprehensive tutorial
on the subject in place of a good sound course in physiological optics.
Previous reports under this project include:
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(1) Letter report, September 24, 1965 - included preliminary discussion
of wavelength discrimination.
(2) Letter report, October 28, 1965 - included preliminary discussion
of visual acuity and visual threshold.
(3) Quarterly report, December 15, 1965 - March 15, 1966 entitled
"Human Factors Aspects of Photointerpretation."
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Vision is a physiological process which takes place through complex
interaction of retinal receptors in the eye, nerve connectors, and brain.
A great deal of impressive work has been done to explain this process, and
in the past couple of years the physiological mechanisms of vision have
become quite definitely known.
The processes of vision are rather far removed from the experience of
the PI or other worker doing a visual task. What does apply to the experi-
ence of the worker is not the physiology of vision, but the psychophysics of
perception. This is a specialty in which subjective data on perception --
what he sees, thinks that he sees, or says that he sees when confronted with
a stimulus -- are experimentally treated. "Vision" and "perception" are
often loosely and interchangeably used, and this loose usage need not
bother us particularly, once we ourselves have a clear idea that there is a
difference.
Libraries full of fine work have been written on the photochemistry of
the retina, the visual neural pathway, and so forth. This work is one
example of the impressive success of comparative biology with reductionist
and analytical methods. Biologists have tended to focus investigation on
organisms which are simpler and easier to manipulate in the laboratory than
man, not only because this is more socially acceptable, but also because of
a widespread assumption that understanding of man will eventually emerge from
detailed knowledge of the structures that occur in other living forms
(Dubos, 1965). For example, a great deal of physiological experimentation
has been done on the visual mechanisms of clams, horseshoe crabs, cats, and
rabbits. This work is valuable and interesting in itself. Among other
things it has. confirmed the classical theory to tri-receptor wavelength
discrimination in vertebrate eyes (MacNichol, 1964). However, neurophysiolo-
gists insist that we should not force psychological interpretations on the
physical facts that we can record. For example, neurophysiology is not con-
cerned with color perception, but with mechanisms of wavelength discrimination.
Some facts about these mechanisms may lend themselves to interpretation in
terms of visual experience; others are fractional parts of a complex nervous
organization, and cannot be so interpreted (Davson and others, 1962). Even
without these professional warnings, common sense should tell us that the
visual response of an anesthetized cat is not directly applicable to the
perceptions of the photo interpreter.
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In spite of the progress which has been made in explaining the photo-
chemistry of wavelength discrimination, subjective color perception remains
essentially a mystery. It is not a simple response to wavelength, but
depends heavily on the "field" or color world to which the person is sub-
jected. The eye has remarkable "constancy" or tendency to maintain colors
(and shades of gray) in various kinds of illumination. Land (1959) found
that this constancy effect is far more extensive than had been supposed, and
that the eye can in fact create normal colors in a color world much more
restricted than the ordinary daylight world. Colors also possess intrinsic
spatial properties (Nelsen 1943); intense long-wavelength colors change in
hue when viewed continuously, from red through yellow to green (Cornsweet and
others, 1958), probably owing to differential rates of bleaching of the
pigments. In addition, colors have decided emotional effects, as indicated
in studies revealing variations in response to colors as a function of ethnic
or national background.
The visual tasks and functions of the image interpreter can often add
up to a weird combination of undesirable conditions. Visual and muscular
discomfort are imposed, in some degree ranging from minor stress to outright
abuse, by all or nearly all forms of viewing imagery. For example:
(1) All microscope work, especially continual peering, and especially
by persons who wear glasses. Contact lenses would help, but even they cause
their own set of discomforts.
(2) Viewing photos by transmitted light on projection screens or light
tables when light shines into eyes through or at sides of film.
(3) Miscellaneous muscular stresses when equipment and/or photos are
placed so that a person has to hunch over or bend his neck at a sharp angle
for any length of time. Besides causing discomfort, cramped posture tends
to interrupt circulation, leads to headaches, etc.
(4) All forms of improper stereo, including: images which do not
correspond in scale (even within the 10 percent "limit") or orientation;
images which do not have proper stereo base.(i.e., flight line not the same
in sequential coverage); images which have very great parallax exaggeration
or which have so much relief that only parts can be fused at one time;
blink comparison, if done as any more than an occasional stunt to find an
elusive image; and probably, flicker fusion. Binocular fusion is supposed
to be the most delicate adjustment the visual mechanism is required to make.
Even in work with good stereo pairs, we abuse it in a mild way in the process
of orienting the photos.
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(5) Superimposition of images which do not exactly register, as in
negative-to-positive change detection. It is understood from Colwell that
when this was tried they ran out of interpreters in a remarkably short time.
(6) Long-continued work in dark rooms.
(7) Projection, especially rear projection, of moving images, as in
scanning film with the film drive in operation.
Of course, people can cope with a certain amount of physical discomfort
if they see good reason for doing so. However, it is difficult at the
moment to think of another profession in which each technical innovation
piles these stresses up higher. In addition to this, visual discomfort is far
more alarming to the person than ordinary muscular strain. If his neck aches
he may not mind too much, but if he begins to see double, he is rightly
agitated.
It would be interesting to have a reliable account of the number, fre-
quency, and seriousness of mistakes made under various conditions of
intelligence interpretation. Undoubtedly many serious mistakes have gone
undetected because there was no way to check up. Some of these, of course,
are due to honest intellectual error, (i.e., misinterpretation of ambiguous
evidence),but many others must be due directly to the inattentiveness with
which the mind protects itself from unacceptable stress.
Along this line, it is interesting to cite a relatively recent experi-
ment in "visual factors" by the Geological Survey where they took a sufficient-
ly existential view of their photogrammetric plotters to ask their opinions
of the various tasks and working conditions (Moore and Bryan, 1964). The
most interesting thing about this article is the tone of mild surprise
throughout. The results were in fact highly predictable, but had remained
hidden from the Survey as long as they viewed the work merely as a series of
mechanical processes. For example, the Survey had never considered that
they should supply corrected red-blue lenses to people with eye defects.
Instead they made people choose between using clip-ons (uncomfortable and
ineffective) and buying their own. At their salaries, naturally no one
bought his own. Not until 1964 did the Survey (officially at least) dis-
cover that properly-fitted glasses improved a person's work. Similarly,
when scribe coat materials first came in, they were eagerly adopted as a
great boon to map production, and did in fact make a dramatic improvement in
color separation and other reproduction methods. The fact that scribing
violated all the draftsman's principles of fine muscle control through
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relaxation, and forced him to peer at his work at abusively close range to
see what he was doing, was obvious to anyone who ever tried it; but not
until 1964 did it occur to the Survey that loupes might help.
The Survey experiment led to a measurable improvement in performance of
the experimental group. The experimenters seem to assume that this is due
directly to the newly introduced working methods, and much of it undoubtedly
is. But part of it must also be due to the improvement in morale of
employees who had the novel experience of being consulted about their work.
(In industry it has often happened that the performance of experimental
groups kept going up, no matter what changes were introduced, even when all
changes were abolished and the original conditions restored.)
The primary objective of this project has been to sift through the techni-
cal literature and research on visual factors for those factors relevant to
the task of image interpretation. Assumedly, these factors are then appli-
cable to design considerations of interpretation equipment, systems or
operating environment. The phenomenal growth of technology and development
of image exploitation equipment in recent years can only be expected to
continue, probably at an ever accelerating pace.
At the risk of becoming involved in all the complexities of human factors
engineering, it is perhaps useful to try to assess the relationship between
the image interpreter and his equipment. One of the references reviewed
during this project presents an interesting summary that could be germane to
this relationship: Human Factors Design Standards for the Fleet Ballistic
Missile Weapon System, Volume 1, "Design of Systems." Although this manual
was written to cover a wide scope
generalized, its very nature as a
section of it contains a somewhat
synthesizes many volumes of human
between the lines and a sometimes
of the comments can be thought of
equipment relationship. For this
this work for reproduction here:
2.1.1 Sensing
of applications and is therefore very
tutorial contributes to its value. One
philosophical discussion that neatly
factors texts. With judicious reading
loose interpretation or application, many
in terms of the image interpretation/
reason, we have selected passages from
The sensing function consists of the detection of some physical energy
Linformation or signals) originating within the environment of a system.
These signals may originate external
to the system: in radar or sonar returns,
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or in the human senses of vision, hearing, smell, etc. They may also be
developed internal to the equipment, as in the result of switch closures in
equipment or the kinesthetic sense in man. In either case, specific sensors
are required to receive these signals as inputs to the system. The sensing
function is often coupled with transducing, converting, filtering, or
amplifying functions. Equipment examples abound, as in the transformation
of a mechanical signal to an electrical signal, analog to digital conversion,
selection of some portion or all of a signal for amplification, or screening
out some undesired portion of a signal component (e.g., noise).
An important characteristic associated with human senses is the
phenomenon of attention. Although the human being is constantly receiving
sensations from many sources, he is able to select and concentrate on only
those which are of importance to him, much as equipment sensors are able to
filter out various unwanted signals or noise, or to select desired signals.
In addition to attention, the reception of stimuli is influenced by a man's
physical condition (i.e., health, fatigue), as well as by the range of
sensitivity of the receptors.
The phenomenon of attention is closely related to the concept of per-
ception. Human reception of signals would be meaningless without some basis
for their interpretation. This interpretation becomes possible as a result
of experience or learning. This association demonstrates another character-
istic of human perception, that of the symbolic processes associated with it.
Through man's ability to abstract significant details of complex inputs and
to remember them, he is able to apply his experience to other situations
(i.e., he is able to learn). Unlike equipment, perception in man is also
influenced by emotional processes. For example, the performance of a par-
ticular task may be enhanced or degraded depending on the pleasant or
unpleasant memories associated with it.
Thus, the function of perception in human beings is somewhat similar to
those of transducing, filtering, and amplification in hardware systems.
2.1.2 Processing
After the information has been transformed into inputs suitable for use
in a system, it is processed to produce appropriate outputs. The information-
processing function may involve any or all of the following subfunctions:
(1) Measuring (estimating) and comparing external signals against each
other or some stored standard of comparison.
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(2) Integration of various signals with each other and with various
alternative available actions.
(3) Storage of some or all of the information, to be acted upon later.
Transducing, converting, amplifying, and filtering again may be involved.
Information processing in equipment may be performed according to pre-
established fixed programs or may be under the control of a human operator.
Often the rate at which information is received or can be processed is too
great for the information at the time of reception. In these cases, data
may be stored either temporarily or permanently, depending on the require-
ments for their utilization. In equipment memory there may also exist
programs which provide instructions for processing the information.
Man is able to process information based on his perception of the signals
which he receives and upon stored information. This integration of external
and internal information,as the basis for identification or selection of
appropriate courses of action, is often called decision making. Although
decision-making tasks reflect an emphasis on only certain aspects of human
information-processing capabilities, they have become a focal point for
discussing man's processing capabilities. The processes which support the
decision-making capabilities of man include abilities for qualitative esti-
mations, comparisons, judgment, transformation, coding and decoding,
inductive and deductive reasoning, abstraction and conceptualization,
memorization and recall, and prediction. The result of these capabilities
is to make man much more flexible than machines as a data processor -- at
least in the present stage of technological development. Through appropriate
training, man is able to deal with changing situations and unforeseen
problems in the absence of a specific program. Unlike a computer, man can
continuously develop and modify his own programming. In other words, he can
learn. Closely associated with man's decision-making function is his
memory or storage capability. Memory is the retention of what is learned
and, conversely, forgetting is the failure to retain what is learned. With-
out memory, at least in the biological sense, there could be no learning;
each occurrence of a signal would elicit the same response as before and
there would be no modification or reprogramming of behavior. The capability
of man to remember and to modify his behavior through learning accounts for
much of his flexibility as a programmer of computers. Much of what is
remembered, and the ability to manipulate and combine this information
(thinking and reasoning), is the result of man's symbolic processing capabil-
ity. What is retained is in the form of words, numbers, or images which
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represents abstractions or symbolizations of what is learned. This capability
for abstraction and conversion to symbols of large amounts of information
accounts for much of mans superiority over machines in decision making.
2.1.3 Actuating
Once a desired action has been identified or selected as a result of
information processing or decision making, it is necessary to implement this
action. Regulation in man involves the organization or patterning of his
responses so that they will occur at the proper time, in the proper sequence,
or in the proper combinations. For example, when learning to perform a
procedure, an operator must refer to manuals or otherwise seek guidance to
learn how to perform the procedure. Eventually, these responses become suffi-
ciently learned so that the procedure is performed rapidly and accurately as
a perfected and completely organized skill without any external supports. As
skills are mastered, they are performed more and more automatically and
involve less conscious effort or thought on the part of the individual. For
the learning of complex knowledges, as might be required for high-level
decision-making tasks, a similar organization of responses may take place if
similar situations occur often enough; otherwise, man may exhibit considerable
variability and disorganization in his behavior.
Also related to the regulation function in systems is the concept of
feedback. Many semi-automatic or automatic devices or systems have one or
more sensing or monitoring circuits which feed back information on the opera-
tion of the system to provide a basis for regulation and action. Such feed-
back loops are the distinguishing feature of closed-loop systems as opposed
to open-loop systems. In many systems a human operator or monitor is
depended upon to close the loop. Responses within the human himself, as with
closed-loop hardware systems, exhibit feed-back characteristics. This is
generally referred to as knowledge of results and may be of two general types:
internal, resulting from sensations associated with bodily movements or the
higher mental processes, as might occur in the mental solving of some
problem; and external, resulting from seeing or hearing the results of his
responses such as the change in position of control, change in the status of
an instrument, or change in position of a vehicle.
Finally, to achieve the output -- whether it is information, materials,
or control of other equipment -- all systems have one or more actuation
functions. These require a supply of requisite energy in a form necessary to
achieve the output. In man, this final phase of the behavior process is the
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evocation of some muscle response, either verbal as a command, or as a motor
response such as the movement of the arm and hand to activate a control, or
the movement of the eyes to view some display. Glandular responses also
occur but ordinarily are of less importance from a design standpoint; however
they do affect the level and type of activity of the individual as well as
his comfort.
Two other categories of functioning peculiar to humans should be mentioned,
those of drive and motivation. Drives include such factors as hunger and
thirst and are related to the physiological requirements of the human organ-
ism. Motives are requirements which arise out of the individual's learning
drives, and motives function as energizers of human behavior, and as such
they are somewhat analogous to the power required by hardware systems for
activation.
2.1.4.1 Capabilities and limitations of man and machine.
The table on the following page summaries the relative advantage of men
and machines with respect to the basic task elements just discussed.
Following is a series of general principles taken primarily from dis-
cussions by Swain and Wohl after Fitts, together with some additions and
comments pertinent to the assignment problem in general.
(1) Ability to detect certain forms of stimuli. The ability to detect
certain stimuli (e.g., smell, taste), especially stimuli which are not read-
ily sensed inorganically, is one of man's characteristics.
(2) Sensitivity to a wide variety of stimuli. Man is sensitive to a
wide variety of stimuli through the use of the organs of sight, hearing,
smell, touch, temperature, pain, taste, balance, and muscle sense (kinesthesis).
All of these sensory abilities are used in operating and/or maintaining equip-
ment, though obviously some are used much more than others. In spite of this
wide variety in sensitivity, the precision of sensitivity in any one mode is
quite restricted compared to machine "sensing ability."
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Advantages of Humans
Detect low levels of energy
Sensitivity to a wide variety
of stimuli
Perceive patterns and general-
ize from them
Detect signals in a high-noise
environment
Store and recall large amounts
of information
Exercise judgment
Improvise and adopt flexible
procedures
Handle low probability events
Arrive at new and different
solutions to problems
Profit from experience
Track under a wide variety of
situations
Reason inductively
Perform fine manipulations
Task Element
A
C
T
U
A
T
I
N
G
Advantage of Machines
Sensitiveity to stimuli outside
of man's ability
Insensitivity to extraneous
factors
Monitoring of other machines
or men
Respond quickly to control
signals
Store and recall large
amounts of data for short
periods
Computing ability
Handling of highly complex
parallel operations
Deductive logical ability
Perform routine, repetitive,
precise tasks
Exert large amounts of force
smoothly and precisely
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(3) Ability to perceive patterns and generalize about them. Man has
this ability, even though the patterns may change in size or position or may
be partly masked by noise. However, this ability (perceptual constancy), as
it applies to certain types of activities, is often difficult to learn.
Interpretation of patterns of light by human operators (sometimes required by
certain computer programs) may be extremely difficult to learn. Waveform
analysis is considered by many maintenance technicians to be the single most
difficult perception required in test and checkout, and differences of
opinion often exist between technicians in interpreting waveforms. Therefore,
it is ordinarily advisable to search for ways to avoid waveform or light-
pattern analysis, especially where relatively low-skilled personnel may be
employed. However, if data can be encoded and displayed in such a way that
the personnel can use their perceptual capability to the maximum (i.e., if
adequate "pictorial" or familiar "patterned" displays are used), then they
will be very good at sizing up complex situations quickly.
(4) Ability to detect signals (including patterns) in high-noise
environments. This ability is related to the use of various types of opera-
tional cathode ray tube displays, to much aerial photography, and to reception
of auditory signals. One shortcoming to this human ability is the human
tendency to fill in gaps in the displayed information on the basis of expect-
ancies. When these expectancies are not valid, the human operator or tech-
nician may see something that is not there or may miss out-of-tolerance
indications not in line with his erroneous expectancy. This human limitation
applies mostly to monitoring tasks, somewhat less to routine operating and
maintenance tasks, and least to trouble location tasks where the man knows
something is wrong and is searching for out-of-tolerance indications.
(5) Ability to store large amounts of information for long periods and
to remember relevant facts at the appropriate time. This ability is related
to the human's superior ability to use judgment, to improvise, and to respond
appropriately to low-probability occurrences. The human is said to be
capable of storing from 1.5 million to 100 million binary bits of information.
Man's memory of facts is less reliable than machine memory, but he does fairly
well at remembering principles, strategies, contingencies, and other rules
and their applications, provided he has been properly taught.
(6) Ability to use judgment. It is difficult to define "judgment",
although we all seem to know what it is. Perhaps man's superior ability to
use judgment is related to his ability to handle concepts, ideas, and other
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data which are not easily quantified, and to arrive at a decision on the basis
of some unspecifiable comparison of nebulously defined alternatives, even
when the situation is unique. Machines are not yet very efficient in the
kind of selective, long-term storage needed for handling unique problems, and
they cannot be fed any variable that cannot be encoded. Thus, judgment is
very important where the population of events cannot be completely defined-
(7) Ability to improvise and adopt flexible procedures. The human can
reprogram easily and quickly and can vary performance tolerances quickly. He
can acquire new methodological know-how simply by reading printed verbal pro-
cedural directions. Human flexibility helps avoid complete breakdown in
emergencies.
(8) Ability to handle low-probability alternatives (i.e unexpected
events). The human may not always employ an adequate strategy in dealing with
rare events. In fact, he generally tends to try several strategies which
have worked before for more familiar events, and he tends to repeat unsuccess-
ful strategies or to just "Easter egg" (i.e., attempt random activities).
This characteristic is not restricted to relatively unskilled personnel. if
low-probability events can be programmed into a machine, the machine will be
more efficient, because there is no forgetting. However, if the population
of possible low-probability events is large (the usual situation in command/
control and checkout operations), then the storage capacity required to
handle them poses problems for the machine. On the other hand, properly
designed procedures, coupled with adequate training, can markedly increase
the average man's facility to respond to the unexpected.
(9) Ability to arrive at new and completely different solutions to
problems. The human can employ originality in putting to use incidental
intelligence picked up during his training or experience. Unfortunately, he
sometimes may try the novel when the usual would be more appropriate. This
partly explains the often-observed tendency for the technician to "tinker"
and for the operator to "over-adjust" rather than follow the prescribed
procedures. Probably a more complete explanation should also refer to the
usual inadequate design of procedures.
(10) Ability to profit from experience. Ability to profit from exper-
ience, that is, to modify responses on the basis of prior events, is another
of man's characteristics. It is not used to its maximum in operating and
maintenance situations because of lack of a formal organization and procedure
for incorporating and disseminating a body of operating or maintenance
knowledge. Thus, system management policies will often prevent a system from
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taking advantage of experience. Although machines have been built that can
"learn" from experience (e.g., chess players and maze runners), the cost and
volume required for such machines is much greater than for an equivalent man
(11) Ability to track (i. e. , act as a servo follow-up) in a wide
variety of situations. The ability to track (i.e., follow or center a
moving target) is more pertinent to operator positions than to maintenance
positions.
(12) Ability to perform when overloaded. The human is capable of with-
standing high conditions of loading that might cause a complete breakdown in
a machine. That is, the human frequently can perform at a less optimum rate
or at a lower level of proficiency under high-load conditions, but he usually
can continue to perform. This quality of "graceful degradation" is found in
some machines, but to a lesser degree than in humans. However, this human
ability is related to man's ability to generate his own inputs, and the nega-
tive side of this ability is the possibility that these inputs may be
irrelevant to a solution. Thus, the human introduces internally generated
"noise" to the man-machine system, and this can be part of the "overload".
(13) Ability to reason inductively. Man can reason inductively; that
is, make generalizations from specific observations. Along with judgment,
this is perhaps man's greatest claim to fame. It is especially important in
decision making.
(14) Ability to perform fine manipulations. This superiority of man is
especially important in assembly/disassembly operations, fault correction
(e.g., soldering, replacing tubes, etc.) and in the fine adjustments required
in calibration and alignment. Machines built to perform this type of manipu-
lation are frequently extremely costly and complex. However, precise manual
adjustments often must be aided by a machine; for example, a receiver tuning
device or a torque wrench with a read-out in foot pounds. And those manipula-
tions involving complex eye-hand coordination are difficult to learn to a
high skill level.
2.1.4.3 Characteristics tending to favor machines over humans
(1) Sensitivity to stimuli. Machines can sense forms of energy in bands
beyond man's spectrum of sensitivity; for instance, infrared and radio waves.
(2) Insensitivity to extraneous factors. Machines have a greater
insensitivity than man to extraneous factors. They have no morale problems.
They do what they are told to do. Perhaps this is at once the machine's
greatest advantage and its greatest disadvantage. The advantages tend to be
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emphasized by design engineers, especially those who have seen equipment mis-
used in the field. The disadvantages tend to be emphasized by field
personnel, especially those with high levels of skill who see aspects of this
skill being replaced by machines.
(3) Monitoring other men or machines. A great deal of research evidence
(both experimental and field observational) collected by North American and
British researchers shows that man is a poor monitor of infrequently
occurring events as well as frequently occurring events over a long period of
time. Man becomes distracted or just bored. The evidence is so overwhelming
that Fitts, et al.,have declared that machines should monitor humans rather
than vice versa. This principle has important implications for the design of
semi-automatic equipment, as will be discussed in the next major heading.
A corollary to the above principle is that man should not be the sole check
on the accuracy of his work.
(4) Responding quickly to control signals. Machines have microsecond
lags, whereas the shortest which can be expected from man is about 200 milli-
seconds, and this only if he is set to make a movement upon the receipt of a
go/no-go signal. If a decision is required, the human response time increases
rapidly. Moreover, man becomes fatigued rapidly under conditions requiring
a series of rapid decisions. Speed, then, is one of the primary qualities of
machines.
(5) Storing and recalling large amounts of precise data for short
period of time. Especially in the computer field, there are requirements for
short-term storage of information ("scratch pad" data), followed by complete
erasure of the data in preparation for another task. Machines excel at this;
humans not only have difficulty memorizing large amounts of information, but
their recall is often spotty and they have difficulty in completely erasing
information in short-term storage.
(6) Computing ability. People make errors even in the simplest conver-
sions of data requiring no more than simple arithmetic. They are poor at
quickly performing-highly complex calculations. Such calculations as higher
order integrations pertinent to some types of navigation and fire control
computations, are beyond the capability of humans. However, machines are
limited by the rules of operation that are built into them. In some cases,
humans can arrive at an adequate answer more quickly by a series of approxi-
mations that eliminate unnecessary precision.
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(7) Handling of highly complex operations (i.e., doing many different
things at once. Fitts, et al., states that when man has to employ his highest
intellectual abilities, he is essentially a one-channel computer -- he can
work effectively at solving only one problem or attending to one thing at a
time. Only when he achieves very high degrees of skill can he work on more
than one thing, and then only by rapidly shifting back and forth. The
machine, however, is limited only by the capacity built into it.
(8) Deductive logical ability. Machines are much quicker and more
reliable than humans in identifying a specific item as belonging to a large
inclusive class and in using rules for processing information. If an opera-
tion can be programmed 100 percent, then a machine can be built to perform '
the operation rapidly and accurately with perfect repeatability. However and this is often overlooked -- procedures can be built to enable a human
to follow the rules efficiently, though less rapidly, and with a small probabil-
ity of error.
(9) Performance of routine, repetitive, precise tasks. Man is notor-
iously prone to commission of errors in such operations. As in monitoring
tasks, he becomes easily distracted or he may perform some non-prescribed
action out of sheer boredom. However, if the task is sufficiently repetitive
that it can become automated, then the operatoons involvement in and awareness
of what he is doing can be reduced to a minimum and he is free to think of '
other things.
(10) Exerting large amounts of force smoothly and precisely. The
human is no match in strength for even the simplest lifting or moving devices,
and his control movements with large objects tend to be erratic and subject
to oscillation, especially when the emphasis is on speed.
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Discussing the complexities of color (see Dimmick, 1964), Hering, in
1878, pointed out that the physical, the physiological, the psychological,
and the "common sense" concepts of color are completely different. "The
layman," says Hering, "believes the green of a leaf to be a property of that
leaf. The physically informed person, however, regards the green, not as
an attribute of the leaf, but as a characteristic of the rays reflected from
the leaf and names them green. The physiologist goes further. He knows
that the green is not truly a part of the rays reflected to the eye but,
instead, depends upon the visual organ. With the. same validity with which
the laity considers green as an attribute of the leaf, and the physicist
regards the reflected green as a property of the rays, he speaks of a green
impulse in the visual organ. Finally, for the psychologist, green is neither
a property of the leaf nor of the ray nor of an impulse in the eye, but is
instead a mental fact. To be sure, he grants it to be dependent upon a
nerve process, but he discriminates between the postulated physical cor-
relate of the phenomenon and the phenomenon itself."
The very narrow portion of the electromagnetic spectrum to which the
eye is sensitive is generally considered to be about one octave, from about
380 to 760 m~t, although wavelengths as low as 313 m4 and as high as 1 m4
may sometimes be seen. This objective, or physical, light is able to
stimulate the retina, and the nerve impulses which it sets up, when con-
ducted to the brain, evokes the sensation of light. When all the wave-
lengths within this visible band are present, the resulting sensation is
that of white light. When these vibrations are separated by a prism or
grating, a spectrum of the light appears.
As an introduction to the processes of color vision, it is worthwhile
to review briefly the duplicity theory of scotopic and photopic vision, and
the nature of the visual system. In particular, a knowledge of the char-
acteristics and functions of the retina are essential to the study of
color.
The photodetection system consists of a retinal mosaic of some
127,000,000 receptors. Of these, about 7,000,000 are cones which provide
high-acuity daylight or photopic vision and color appreciation, and about
120,000,000 are rods which are highly sensitive to low-light levels and
are essential to scotopic or night vision. The dark-adapted rods contain
a material known as rhodopsin or visual purple which becomes bleached in
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the presence of light. This forms lumi-rhodopsin which, in the living
retina, breaks down thermally to retinene and then to a protein called
opsin. A form of the retinene also breaks down to vitamin A, passing
out of the receptors into the pigment epithelium which, with the blood,
resupplies vitamin A which in turn is needed to rebuild rhodopsin. Thus,
the importance of an adequate diet of vitamin A is apparent. It is only
necessary to understand, in an oversimplified statement, that the visual
purple molecule, which is a union of a simple protein and vitamin A, under-
goes decomposition under the influence of light. Some of the products
formed stimulate the rods, directly or by the intervention of another
chemical reaction, thereby generating a nerve impulse. In the absence of
light, visual purple is resynthesized. Both the rebuilding and the de-
composition take place simultaneously, the extent of each being determined
by the intensity of the light. (Zoethout, 1947)
Exposure of the rods to light does not evoke the sensation of color.
However, different parts of the spectrum, when viewed by the dark-adapted
eye at low-light levels, appear to have different luminosities with the
brightest region being near 510 m?, or what would be the blue-green part of
the spectrum. Longer wavelength red lights are hardly seen at all, with
only slight improvement in the deep blue or violet regions. This relative
lack of sensitivity to red light is the reason why pilots, for example,
when preparing to fly night missions will spend some time becoming "dark
adapted" in a room illuminated with red light. However, by reducing the
energy of the illumination sufficiently, it probably makes little difference
as to the color of the light. The main advantage is that when one color
is used as the adapting stimulus, the eye gradually loses sensitivity to
that color, so in general the blue-green region, to which the dark-adapted
eye is most sensitive, is avoided as an adapting light.
The photoreceptors known as cones are considerably less sensitive than
the rods and become active only at light levels of about 0.25 meter candles
or greater. Under daylight or photopic conditions, colors can be seen, and
the visual acuity improves. Cones are found throughout the retina but have
a maximum concentration in a small central area known as the fovea, which
is the region of maximum visual acuity. While there are some cones through-
out the retina, there are no rods at all in the fovea. The maximum con-
centration of rods is about 20 degrees from the center. Thus, because of
the cone distribution, some color can be seen near the periphery of the
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field-of-view if the light level is high enough. At very low-light levels,
objects which cannot be seen at all by looking at them directly can some-
times be seen by turning the eye so that the more sensitive rods are
illuminated.
Whereas the eye in scotopic vision is most sensitive to light at
510 m?, it is most sensitive in daylight or photopic vision to light at
a wavelength of 555 m4. As a matter of fact, the whole spectral sensitivity
curve shifts toward the higher wavelengths in photopic vision. This shift
in spectral sensitivity is known as the Purkinje shift, or phenomenon.
For light to be seen it must first of all be absorbed by a photo-
pigment in the eye, which produces some change capable of starting the
complex neural events involved in vision. Chemistry of rod photopigment
has been studied in detail; color vision, which depends mostly on the cone
photopigments, has been notoriously difficult to investigate. (De Valois
and Abramov, 1965)
A color is generally characterized by three qualities: hue, brightness
and saturation. However, as Evans (see De Valois and Abramov, 1965)
pointed out, with a spot of light on a background one no longer has a simple
three-variable color vision system. The colors perceived in various
stimulus situations involve manipulation of six psychophysical variables
of luminance, purity, and dominant wavelength for both the stimulus and
the surround, and this in turn presents four independent variables: the
three mentioned above of hue, saturation and brightness, but also grayness,
with each quality influencing the other.
Hue is that sensation determined by wavelength which is what is
ordinarily meant when the word "color" is used. The general recognizable
hues are named red, orange, yellow, green, blue, indigo and violet. Each
of these merges by imperceptable gradations into its neighboring color.
Red gradually changes to an orange-red, reddish-orange and then to orange,
and so on without specific boundaries. Actually a large number of hues can
be recognized, but only a relatively few receive names.
There are certain portions of the spectrum where small differences in
wavelengths give rise to large differences. in color sensation. Hue dis-
crimination is particularly acute in the yellow, near 585 m?, and somewhat
less so near 497 m4 in the bluish-green. There are also two much smaller
peaks in the orange (636 m?) and blue (435 m4), but elsewhere hue dis-
crimination or hue sensibility is much less acute. At each end of the
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spectrum, beyond about 655 m? at one end and 430 mj, at the other, there
is very little change in color sensation as the wavelength is changed.
For each psychological phenomena (hue, brightness and saturation)
there is a physical counterpart of wavelength, the physical intensity of
light, and the absence of white light, respectively. Color names often
refer to hue-saturation combinations, such as "pink," which is basically
red but has a large white component and is therefore a desaturated red.
There are a number of pairs of colors which, when viewed together,
produce white light and which, following exposure to one, produce an after-
image of the other. Furthermore, adaptation to one color and then viewing
another may produce "supersaturated" colors. These hues are known as
complementary colors. Every spectral color, except for the greens, has
a complementary color. Since complementary colors produce white in which
the hue of each is destroyed, they mutually exclude each other. Thus, a
reddish-green or greenish-red does not exist as does a greenish-yellow or
yellowish-red.
While numerous theories have been advanced about why humans and a
limited number of animals and fishes actually can experience the sensation
of color, none have yet adequately explained this phenomenon. However,
there is sufficient evidence, either implied or direct, which leads to the
conclusion that there are very few different types of cones, each sensitive
to a different color. The eye, unlike a spectroscope, cannot tell what the
components of a particular color are. Any color, or hue, can be matched
with no more than three primary colors in various amounts, forming what is
known as a metameric match. (Sometimes, however, one of the colors has to
be added to the color to be matched.) Furthermore, various combinations of
red, green, and blue will give the appearance of white light. Because of
these phenomena, most investigators have tended toward a three-component
color theory. Indeed, MacNichol (1963)has found clinical evidence in the
retinas of goldfish which tends to support this. Nevertheless, in recent
years Boynton and others have proposed a four-component theory which also
makes quite a bit of sense. It has been noted that there are four color
sensations which are psychologically unique. These are known as the primal
or psychologically pure colors of red, green, yellow and blue. To bolster
the argument of four primal colors, it is noted that while color matches
are maintained despite luminance differences, hue is likely to shift, with
the notable exception of the four wavelengths which yield the primal hue
sensations.
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It is very interesting to note that in spite of these theories, Land,
in 1959, dramatically demonstrated what appeared to be full color from only
two wavelengths. Furthermore, it did not matter greatly what these wave-
lengths were to produce this phenomenon: just a long wavelength record and
a short wavelength record. It has been stated that this occurs as the
result of color contrasts, or the induction of one color by the color of
its background. Whatever the cause, it is known that the apparent color
is often influenced by the observer's memory of the scene, or by what he
thinks it should look like. Also, the apparent color of a scene, which has
been masked off, looks significantly different when the: mask has been re-
moved.
In 1959, after the appearance of Dr. Land's now famous article in the
Scientific American, the principal investigator, along with D. S. Ross,
extended the idea of a "long" and "short" record to a combination of
infrared and monochromatic visible light to produce some startling results
having application in camouflage detection.
The so-called Land process of recording photographic images using a
two-color separation process and recombining with the same colors, or
almost any colors desired to produce "natural" or "false" colors, finds
important applications in reconnaissance photography. The process has the
possibility of providing two very high resolution black-and-white negatives
which can be viewed as is or recombined as a color representation of the
original scene. This technique can often yield higher resolution and some-
times better color rendition than a conventional color film pack.
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The common meaning of "fatigue" -- the subjective sense of tiredness --
embraces three things: true physiological fatigue, or the state of one's
metabolism; visual adaptation (often erroneously called "visual fatigue")
or the state of one's receptor cells; and an individual's mental/emotional
attitude at a given moment. Of the three, assuming that a person is not
absolutely disabled from true fatigue, the last is probably critical in
working circumstances. However, it is not amenable to study. Visual
adaptation is responsive, but its applicability to the PI operation is not
entirely clear.
Zoethout states that the physiological state of fatigue of the bodily
structures reflects itself in the psychological sensation of fatigue which
may be either general or local. General fatigue is often experienced at
the end of the day, even though this has not been spent in any great de-
gree of physical or mental exertion. Local fatigue is associated with the
physiological fatigue resulting from the continued and fairly rapid activity
of certain muscle groups. However, regarding the visual apparatus, actual
retinal fatigue has never been demonstrated. Ocular fatigue, or so called
"eye strain" manifests itself by the well-known symptoms of a dryness and
a smarting of the eyes, often accompanied by eyeache and headache when the
work is very severe. Actual visual acuity is only slightly affected, if
at all, during periods of long observation. Also, the amplitude of con-
vergence was found to be virtually unchanged in a large majority of subjects
tested.
The subject of fatigue, as commonly understood, in delicate visual
tasks such as photointerpretation is admirably summed up in one sentence
in the book by Le Grand: "Fatigue, which is a reduction of activity due
to an accumulation of waste products which the body must get rid of in order
to regain its energy . . . . being almost inappreciable for a certain time
but then showing a progressive lowering of activity."
What is often meant by "vision fatigue" is really "efficiency time."
If we kept strictly to "vision fatigue" we may quote Davson to the effect
that when a subject is tired or unwell his range of uncertain seeing in-
creases. This is the range within which he is likely to fail to detect
a weak stimulus, to report that he detects a stimulus when in fact there
is none (this happens in the most faithfully controlled experiments), or
both. In fact the unreliability of experimental subjects, who report
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"seen" when there is nothing to see, could be rather, directly applicable
to PI working conditions.
4.1 Sensory Deprivation
Certain effects or phenomena which are often attributed to "fatigue"
are more properly traceable to sensory deprivation. This has nothing to
do with "vision" as such, but a great deal with perception and cognition.
The subject came up during the war in studies of the visual in-
efficiency of radar operators, and seems also applicable to photo-
interpretation. From these studies we have an interesting example of the
effects of combined physical monotony and emotional pressure on radar
operators (Heron, 1957). Men on anti-submarine patrol sometimes failed to
find U-boats, which did, in fact, appear
worked in isolation, watching the screen
A laboratory experiment was constructed,
as nearly as possible. The experimental
images declined seriously within half an
Of course the trouble with this experiment
on the radar screens. These men
continuously for long shifts.
duplicating the combat situation
subjects' efficiency in detecting
hour.
is that it reproduces the
monotony, but not the pressure of imminent danger on a passive individual.
Danger used to be considered a'stimulus to alertness, and probably. correctly
so in the days when the appropriate responses were active ones. For the
radar operators, the stimulus (if any) of imminent danger was ineffective
against physical monotony; or perhaps contrariwise, instead from stimulating
them to alertness it combined with monotony to reduce their efficiency.
An interesting series of experiments has been done on the effects of
sensory deprivation on the mind. Subjects placed in a rigidly monotonous
environment suffered almost immediately from impairment of thought,
presently from delusions of persecution and alarming hallucinations.
(Complete darkness and silence proved less damaging than dim diffuse light
and low continuous noise.) When restored to normal environment after
several days, the subject suffered severe perceptual derangements:
apparent movements of objects, distortion of shapes and colors, and
continued hallucinations whenever they closed their eyes. Some people
were affected to the point of nausea or fainting. In fact, these people
experienced a temporary disintegration of the personality. Similar
hallucinations have also been reported in experiments which exposed sub-
jects for long periods to blank visual fields or flickering light.
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The experimenters (Heron 1957 and others) concluded that the normal
functioning of the brain depends on a continuing "arousal" reaction main-
tained by a constant bombardment of sensory stimuli. However, the stimuli
lose the power to maintain this arousal if they are restricted to repeated
stimulation in an unchanging environment.
Photointerpreters in scientific fields are protected from some of
the above conditions. Photointerpretation for the scientist is not a
profession, only one of many techniques. He does not indulge in much
experimentation with sophisticated viewing methods. He is not usually under
emotional pressure. He is free to study and consider the photographic
images on his own schedule; he can drop photointerpretation for study or
field work whenever it seems desirable; and he is internally motivated by
intellectual interest in the images he looks at. However, the motivations
which act on intelligence interpreters are extremely varied and virtually
impossible to categorize or measure.
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Stereopsis as a visual process in image interpretation involves a
complex mixture of physiology, perception and psychophysics of vision.
Time limitations have prevented an exhaustive search and compilation
of the literature on this topic for this project along with any succinct
summation of finds. A thorough analysis and presentation of this topic
alone could be a separate project of considerable magnitude.
As a preliminary indication of research performed in this area,
selected references are listed below:
M. H. Salzman, "The Place for Vision Testing in Photogrammetry",
Photogrammetric Engineering, Vol. XVI, No. 1, pp. 82-94.
A. Anson, "Significant Findings of a Stereoscopic Acuity Study",
Photogrammetric Engineering, Vol. XXV, No. 4, pp. 607-611.
R. F. Dwyer, "Visual Factors in Stereoscopic Plotting", Photogrammetric
Engineering, Vol. XXVI, No. 4, pp. 557-564.
Joseph B. Theis, "A Key Link in the Photogrammetric Chain - The Human
Being", Photogrammetric Engineering, Vol. XXIX, No. 2, pp. 253-258.
Elton J. Gumbel, "The Effect of the Pocket Stereoscope on Refractive
Anomalies of the Eyes", Photogrammetric Engineering, Vol. XXX,
No. 5, pp. 795-799.
Sandor A. Veres, "The Effect of the Fixation Disparity on Photo-
grammetric Processes", Photogrammetric Engineering, Vol. XXX,
No. 1, pp. 148-153.
Kenneth N. Ogle, "Stereoscopic Depth Perception and Exposure Delay
Between Images to the Two Eyes', JOSA, Vol. 53, No. 11, November
1963, pp. 1296-1304.
Duane Lyon, "Let's Optimize Stereo Plotting", Photogrammetric
Engineering, Vol. XXX, No. 6, pp. 897-911.
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APPENDIX A
SPIE SYMPOSIUM
"THE HUMAN IN THE PHOTO-OPTICAL SYSTEM"
ABSTRACTS AND COMMENTS
1
On April 25-26, 1966, the principal investigator attended the "Human in
the Photo-Optical System" seminar in New York, presented by the Society of
Photo-Optical Instrumentation Engineers and co-sponsored by the United States
Army (GIMRADA). The program indicated this was to be "a seminar-in-depth
devoted to the manner in which data is optically presented to an observer
and the way he analyzes or interprets that data." For the most part, this
was true, although. some of the papers strayed either into border areas of
industrial sales promotions or into , regions of psychology where the practical
significance was not particularly evident.
It is felt that it would be sufficiently worthwhile to reproduce the
abstract of each paper as it appeared in the program, along with some
comments of the investigator. Not all of the papers listed in the program
were actually presented, but the abstracts appeared interesting enough to
warrant publication with the rest.
The seminar keynote address was presented by Captain John K. Sloatman,
Commanding Officer and Director of the U. S. Naval Training Devices Center,
Port Washington, N. Y. He stressed the need for simulation fidelity in
training. To satisfy this fidelity he stated that psychological and physio-
logical studies are necessary to determine what visual skills are important
and what can be presented in nonenvironmental training. He emphasized the
requirement for realism in fire control trainers, aircraft simulators, and
the like.
SESSION I
VISUAL REQUIREMENTS IN PHOTO-OPTICAL SYSTEMS
Session Chairman: Dr. Joseph Zeidner, Army Research Office
THE ROLE OF THE HUMAN FACTORS SCIENTIST IN DETERMINING VISUAL
REQUIREMENTS FOR PHOTO-OPTICAL SYSTEMS
1
Dr. Jerome Siegel, Chief - Human Systems
Systems Management Division
Kollsman Instrument Corporation
Elmhurst, N. Y.
"There is very little awareness that the majority of Psychologists
working as Human Factors Scientists have been trained in a broad
spectrum of the behavioral sciences. A very critical part of this
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training is in the area of vision. This knowledge can be extremely
significant in generating visual requirements for the design of photo-
optical equipment which is to be used by an operator.
"The Human Factors Scientist first takes a very meticulous look at the
system and mission requirements and corresponding tasks which are to be
performed by the optical equipment/human eye interface. On the basis
of certain empirical data, such as visual acuity curves, visual thresh-
old data, contrast discrimination relationships and visual perception
data, a number of preliminary conclusions can be made concerning the
visual input requirements necessary for the photo-optical system so
that an operator can successfully perform his task to satisfy mission
requirements. Several specific examples using classifical visual
curves will be presented to demonstrate how visual requirements can be
established using analytical and experimental techniques. These
illustrations will include studies on an optical viewfinder for lunar
target detection; a target detection problem using a TV display system;'
a missile tracking radar display system."
Dr. Siegel indicated that most human factor studies are geared for
vision. Relationships such as that of stimulus-response, familiar in
psychology, apply in such visual functions as brightness thresholds. The
trade-off factors in equipment design are based on knowledge of human visual,
physiological and psychological factors. Among these factors are a knowledge
of the functions to be performed, the control actions required, and operator
task requirements. In addition, information is required regarding environ-
mental data, weight, size, target shapes, color and motion. Among the system
variables to be considered in equipment design are the field of view,
magnification, resolution, contrast, look angle, and monocular or binocular
viewing.
John F. Coughlin
Perkin-Elmer Corporation
South Wilton, Connecticut
"Controlled studies that seek to explore the role of the human observer
in the evaluation of photographic images are possible only when stimulus
material is employed whose objective quality is well known. When such
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studies involve the imagery of complex photo-reconnaissance systems,
the necessary stimulus material is difficult to acquire due to the
variability in image quality and inadequate means of evaluating such
images.
In view of these difficulties, techniques have been developed whereby
the prerequisite stimulus material can be prepared in the laboratory
by simulating the characteristics of the photographic system. These
techniques will be discussed, typical stimulus material will be
displayed, and applications in the field of psychophysical experiments
will be considered."
s
Comments:
Mr. Coughlin described the laboratory preparation of photography for
psychophysical stimulation. In this context, the psychological aspect meant
data extraction from photographs, and the physical aspect was in regards to
the actual film/camera characteristics and the photographic image.
To generate variables for simulating conditions which might be expected
in operational systems, it is possible to alter photographs by altering the
transfer function. The, technique basically consists of projecting a source
energy distribution through a pinhole aperture to an image energy distribution.
The aperture plane can be apodized, or controlled in transmission. The com-
bination of aperture transparency plane control, along with control of the
object energy distribution, produces an output related to the convolution
of the spread functions of the source and aperture. Through this technique,
various models can be generated which can include, among other things, the
effects of haze and film granularity. It was pointed out that it is possible
for someone to extract considerable detail from even a badly degraded image.
DEVELOPMENT AND EVALUATION OF A NEW TECHNIQUE FOR MEASURING IMAGE QUALITY
Dr. Robert Sadacca and Dr. Robert Brainard
Army Research Office
Washington, D. C.
"An image catalog containing a standard set of images having diverse
scene content and quality was developed. Each image in the catalog
had associated with it indices of image interpretability based on
measures of the performance of interpreters who previously interpreted
the images.
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"In application, the catalog approach requires an interpreter or other
judge to compare any new or "test" image being assessed with images
in the catalog and to select that catalog image most similar to to the
"test" image in regard to judged image quality. The indices associated
with the selected image are then taken as measures of the interpret-
ability of the "test" image.
"This catalog technique for the measurement of image quality proved
quite valid and compared favorably with techniques using judgement
for physical variables alone."
The authors sought a quick means to determine image quality for photo-
interpretation screening operations without elaborate mensuration equipment
The technique is to assess image quality by comparison with a catalog of
images. This provides an "index of interpretability" as a measure of image
quality.
The catalog concepts were:
1.
Humans
can judge image quality.
2.
Judges
should be provided a standard context.
3.
Image
quality means image interpretability.
4.
Sample
of images from a population of
scenes.
5.
Sample
of image variants from a given
scene.
6.
Physical, judgmental, and performance
variables are properties of
image variants.
It was interesting to note that the image catalog did not contain
variables in contrast because, over the range of interest, contrast had
little effect. Ground resolution and scale were the most important variables
and provided the best correlation with the catalog. While the point was not
clear, it appeared that in a tactical reconnaissance situation, the photo-
graphic coverage with the best scale and ground resolution would be examined
first, since it would be most likely to contain interpretable information.
This would assume there would be multiple coverage of a given target area
and that these basic criteria could be used in selecting photos for further
examination.
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1
J. M. Heyning
Litton Systems, Inc.
Data Systems Division
Van Nuys, California
This paper discusses the various aspects related to the visual
capabilities and limitations of the human observer, covering both the
physiological aspects as well as the engineering aspects. A brief
outline of this discussion will present the following topics:
1. The physiology of visual perception in terms of the functional
behaviour and control mechanism of the human eye. The former
will be discussed in close analogy to that of a photographic
camera, while the latter relates to specific. functional require-
ments such as target fixation and target tracking in static and
dynamic presentations. A discussion of the limits of resolution
of the human eye will attempt to correlate the physical-optical
and the physiological aspects.
2. The capability of the human observer to detect, recognize, and
identify targets in real-time exploitation of airborne sensor
data. This will be discussed in terms of a graphical presentation
of critical target dimension versus observation time which can be
employed for effective utilization of certain airborne sensors such
as TV, IR line scanner, Laser line scanner, and radar. An analysis
of display systems parameters relevant to dynamic imagery
presentations and interpretation will also be discussed."
Comments:
The first part of the paper was a discussion of Derek Fender's work on
eye tracking mechanisms and the eye as a servo system. (Part of this area
had been previously explored in the December 15, 1965 - March 15, 1966,
Human Factors Aspects of Photointerpretation report prepared by ~nder STAT
this contract.) In the second part, the interpretation of dynamic imagery
(i.e., real-time airborne sensors such as television and radar) was discussed.
It was pointed out that in side-looking radar displays, for short observation
periods, dynamic displays are most likely to result in target detection.
For long periods of observation the reverse is true. With an image moving
from top to bottom an observer tends to scan along the top edge.
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Dr. Helmut Weiss
Aeronutronic Division
Philco Corporation
Newport Beach, California
This paper answers the questions: How much information can a display
screen convey, how large an audience can it serve, and how should
audience and screen be arranged relative to each other?
"It will be shown that in a display intended for group viewing the
individual symbols must be large enough to be legible from a normal
distance equal to the screen diagonal. This condition limits the
capacity of the display, which is found to be independent of the size
of the screen.
"Filled to capacity, a display can only be read from a single viewpoint.
To accommodate a finite audience, it must be used below capacity. For
a given display, there is a well defined optimum screen/audience
configuration which allows the display to be read by the maximum number
of people. If the utilization of a display is increased, its efficiency
decreases (i.e., to permit the display of more symbols, the individual
symbol must be enlarged).
"These relationships are important to the systems man, who should be
aware of the limited capacity of a group display (and the cost of
pushing its utilization too high), to the architect who lays out the
audience, and to the designer who determines the parameters of the
equipment."
Dr. Weiss used the concept of "locus of legibility" to establish
screen sizes for a given audience size and viewing distance. It can be
shown that for vertical bar targets the locus of points of constant
resolution is a circle tangent to the screen. This means that in the oblique
viewing of vertical bars the spaces appear foreshortened and an observer must
move closer to the screen to see bars with a constant visual angle. For
horizontal bars, the locus of points of constant resolutions is a semi-circle
with origin at the target on the screen. It turns out that a letter, whether
it be vertical or horizontal, has the same locus of legibility, and this is
described by the first case as a circle tangent to the screen.
1
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The concept is expanded by considering "three-dimensional circles", that
is, spheres, tangent to each corner of a screen which determine, at their
intersection, the audience volume for a given visual range. By tilting the
viewing screen, and putting the center at eye level, the maximum viewing
volume for an audience can be obtained. This screen tilt is important at
short visual range but not so important longer ranges. It was judged that
better display information could be obtained by breaking a larger screen
into smaller areas arranged around a circle.
Robert S. Scott (Guest Speaker)
Assistant Director
Government Relations
Aerospace Corporation
El Segundo, California
"Nearly 2500 years ago a Greek philosopher named Protagorus observed
that 'Man is the measure of all things.' This unique idea appealed to
Plato who taught his own students and millions more through the ages
the challenging truth of this concept. We may not all agree with the
ancient Greeks. We may not understand what they meant.
"However, we may agree that man is certainly becoming the 'measurer'
of all things. What kind of an instrument is this man, in full measure?
How do we calibrate his brain? How do we affect and control his relia-
bility? What are his sub-systems? How is his operational efficiency
affected by his ambient environment? Are these questions valid to the
human evaluation of the total photo-optical system?
"Are we trying to instrument the man -- or man the instrument? How can
the 'human' in the system improve system operation?
"What can be expected in the future from that living, evolving,
'ultimate instrument' called man?"
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SESSION II
METHODS OF VISUAL PRESENTATION
Session Chairman: Desmond O'Connor, GIMRADA
VISUAL PRESENTATION SIMULATION REQUIREMENTS AND TECHNIQUES
Moses Aronson
Head, Visual Simulation Lab
U. S. Naval Training Center
Port Washington, New York
"The requirements for acceptable visual presentations by simulation
techniques for use in training pilots and other vehicle operators are
defined. The requirements will be defined in terms of the human
operators' visual capabilities. Among the requirements to be discussed
are: What is wide angle? Is color necessary? What detail is necessary?
Light level of the picture; performance characteristics of the flight
simulator or other vehicle simulated which are important to a visual
display/simulator combination; limits of the visual world envelope;
requirements for specific missions, simulator performance envelope and
need for peripheral vision.
"The second portion of the paper will describe some visual simulation
techniques and research hardware developed to date. The compromise and
limitations of the equipment as well as advantages of various techniques
will be discussed. The visual simulation techniques to be covered will
include the shadowgraph/point light source, television and optical
techniques for providing clear day or low visibility conditions."
Comments:
The need for both physical and perceptual fidelity in nonprogrammed,
real world visual simulation systems was stressed. In such systems, it
was pointed out that monocular cues are the most important. A visual air-
craft simulator was described which had an enclosed cabin with a vertical
periscope looking at a model on the ceiling of the room. This system
provided high resolution and wide (76?) field but a small exit pupil.
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Paul T. Kaestner, Vice President
Photomechanisms, Inc.
Huntington Station, L. I., New York
"When generating a display from a scale model for the realistic
presentation of a view as seen from an aircraft or spacecraft, compro-
mises with the real life situation are inevitable. These occur both in
the initial imaging lens and in the final display. Factors such as
resolution, light intensity and true perspective influence the imaging
characteristics, while problems of parallax and image brightness limit
the realism of the display. Fortunately, the choice of the compromises
provides acceptable performance for most simulation systems.
"A typical simulation system will be described and illustrated."
Mr. Kaestner described a telecentric optical system used for a simulation
display. A series of prisms is used to provide pitch, roll and yaw motions.
The image falls on an image orthicon for television display.
J. K. Libby
Fairchild Space & Defense Systems
"This paper describes a recently developed system which enhances the
human decision making capability in analyzing the interpreting aerial
photography.
"Advanced tactical multi-sensor reconnaissance missions provide four
separate rolls of film which require interpretation. Since each roll
of film covers approximately the same area, it is advantageous to view
all four at the same time, with each running at its appropriate speed
so that the same images on all four rolls can be viewed simultaneously.
"The Multi-Sensor Viewer, with its various functions of comparison
viewing of Tactical Target Records, mensuration, printing and processing,
simultaneous scanning, and stereo-viewing will be described. In
addition, a brief discussion of its integration within the Image Inter-
pretation Cell will be presented.
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The Multi-Sensor Viewer was designed and developed as part of the Image
Interpretation Center (IIC) AN/MSQ-58, for the Rome Air Development
Center under Air Force Contract AF 30(602)-2882."
The Multi-Sensor Viewer, installed in a van for tactical use, allows
simultaneous viewing of panoramic, frame, infrared, and side-looking radar
photography. Maps or other cues can be projected on a separate screen for
reference. A mensuration capability with digital readout is provided, along
with stereo viewing of the panoramic and frame coverage. Any one of the four
channels can produce a hard copy print.
TRAINING AND STEREOSCOPIC PHOTOINTERPRETATION PERFORMANCE1
James R. Williams, Human Factors Scientist
Systems Management Division
Kollsman Instrument Corporation
Elmhurst, New York
"Since a previous review of the literature, concerning stereoscopic
performance, had indicated contradictory evidence as to the utility of
stereoscopic viewing in enhancing photointerpreter performance, KIC
initiated an experimental program to investigate this problem. Careful
analysis of the negative studies indicated that subjects were usually
recent graduates of P1 schools and had received relatively little train-
ing on stereoscopy or stereoscopic devices. KIC's approach was to first
determine, via a pilot study, if training would improve stereoscopic PI
performance, and then to experimentally derive training materials to
optimally enhance such performance. Since pilot study results were
favorable, KIC is presently engaged in investigating various training
techniques. One technique which seems to offer many possibilities is
the use of three-dimensional embedded figures. Preliminary data has
indicated that subjects who have had some photointerpretation experience
perform better on 3D Embedded Figures tasks than those subjects who have
not had such experience. Improvements in performance with practice have
also been noted. It is felt that the research with these figures may
result in the development of a successful training approach and, possibly,
an aptitude screening device for photointerpreters."
This study was done in conjunction with Mr. J. Wilde and Dr. J. Siegel
of KIC.
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Comments:
Mr. Williams contended that the so-called three-dimensional embedded
figure task may be useful for screening potential photointerpreters. He
said that in many cases "stereo is a useful tool and should not be over-
looked." Dr. Zeidner, from ARO, commented that Army PI's are currently
screened by tests of stereo, visual acuity, reasoning, and spatial orientation.
He said that such tests have been used by the Army for about 2 years and by
the Air Force for 5 or 6 years.
POSSIBLE EDGE-ADJACENCY EFFECTS IN PHOTOGRAMMETRIC COORDINATE
MEASUREMENT
I
Desmond O'Connor, Senior Research Scientist
U. S. Army Engineer
Geodesy, Intelligence & Mapping Research & Develop Agency
Research Institute for Geodetic Sciences
Fort Belvoir, Virginia
"This paper gives preliminary results of a continuing experimental study
of factors affecting the precision of centering black circular measuring
marks in sharp, high-contrast targets with homogeneous backgrounds,
subtending visual angles up to 45 minutes of arc, in photopic vision.
These targets are designed to simulate the task of measuring coordinates
of artificial pass points in aerial triangulation.
"The results support the proposition that adjacency effects at edges
contain significant visual information, and this would appear to be
important where visual settings are being made by bringing geometrical
configurations into close relationship with one another.
"The maximum information content for the centering task investigated was
contained in ribbons approximately 1 minute of arc wide around the
light areas of target and measuring mark. The most precise pointings
were made by selecting a measuring mark to give a minimum annulus width
within these ribbons irrespective of the target size.
"The results support the concept of a retinal zone approximately
4 minutes of arc in diameter over which acuity is constant, but further
suggest that this may be dependent on the type of task involved.
"The acuity in the horizontal retinal meridian was some 30 percent
greater than that in the vertical meridian for annulus widths up to
4 minutes of arc."
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This paper was particularly interesting and well presented. The
abstract adequately describes the experimental program to determine the
pointing error in centering a small disc within a circle.
The conclusion was that the pointing error in the Y-meridian (vertical)
was about 1.3 times greater than in the X-direction.
The following abstract appeared in the program but the paper was not
delivered at the seminar:
Helen E. Gustafson
Nuclear Research Instruments
Berkeley, California
"Both instruments and humans are needed to extract dimensional data from
photographs and convert it to numerical data for processing and analysis
The human, with his equipment, becomes the interface between the photo-
graph and the computer. The job of an instrument designer is to effect
a match between characteristics of the input and usefulness of the out-
put. One component of this intermediate processing, the human operator,
has certain abilities and limitations which cannot be changed. But they
can be employed to the greatest advantage of the entire process by care-
ful design of the photo-measuring system.
"Since the instrument designer must furnish the user with an effective
link between the photo and final data, he must be concerned not only
with the internal design of the man-machine process, but must also know
the real properties of the photo and the real requirements of the data
reduction program. A good photo-measuring instrument should fit con-
sistently into the entire scheme of acquisition, interpretation,
measurement, data processing, end use.
"This paper will discuss the conflicts and compromises encountered in
measuring instrument design:
1. The photograph itself
2. The measuring instrument's speed, cost, accuracy
3. Visual presentation and its effect on human observers
4. Visual problems of detail, interpreting context, deciding upon
coincidence
5. Instrument output values in terms of its subsequent use deriving
object parameters from image parameters."
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SESSION III
METHODS OF VISUAL ENHANCEMENT
Session Chairman: Paul Pryor, WPAFB
CRITERIA FOR SPECIFYING PROJECTORS FOR THE PHOTOINTERPRETER
J. E. Davis
Aerospace Group
Hughes Aircraft Company
Culver City, California
"A practical approach to specifying and designing large format rear
screen projectors for aerial reconnaissance photography is outlined.
Unique brightness control methods are discussed in terms of their
proper use to keep the interpreter's pupilary diameter at a size to
allow maximum visual acuity. Methods for keeping a uniform brightness
over the screen for different viewing positions is described. Solutions
are outlined for factors contributing to uneven screen brightness such
as the observation angle with the principal axis of the diffusion lobe
of the screen, system vignetting, and cosine4 effects. These solutions
include the use of larger diameter Fresnel lenses, strategically placed
apodizing filters, and a discussion of the Luneburg criteria for
condenser lens design.
"Characteristics of rear projection screening materials are discussed
in terms of their performance in the projection of high definition
(100 to 200 medium contrast lines per millimeter) photographic records.
A system for evaluating screening materials by their modulation transfer
function is proposed. Measurement of the imagery by moving reticles in
the projected field is discussed and the problems associated with
obtaining sharp, fine lines on the screen with this type of system are
summarized. Various light sources and their effects on interpretation,
good and bad, are described. The use of image rotators, both optical
and mechanical, as an aid in angular measurement of the imagery is
outlined.
I
"A formula is developed for an empirical formula for determining the
minimum magnification of a projector based on the resolution capability
of all the elements in the system from film to, and including, the eye
is developed. Also a method for designing projection systems using the
modulation transfer function of each element, including the eye, is
analyzed."
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The paper as
by the abstract.
delivered hardly lived up to the expectations generated
It was, however, pointed out that the resolution of a
viewing screen tends to increase with screen gain, but corner brightness
tends to
contrast
The
fall off. Also, as surrounding brightness levels increase, the
requirements for target areas increase.
empirical formula developed to describe system resolution is
1
+
+
R 1.7
R 1.7 . R 1.7 7
s 1
where Rs = system resolution
R1, R2, etc., are resolutions of individual elements in the system such as
film, screen lens, and the eye.
Martha J. Guastella
Human Factors Laboratory
U. S. Naval Training Devices Center
Port Washington, New York
"Judgement of perceived position under conditions of darkness and
monocular viewing at a 10 foot distance were made of a two-dimensional
luminous target set at varying degrees of rotation with respect to the
observer. A trapezoid was presented randomly and sequentially at
approximately 10 degree intervals throughout 360 degrees rotation.
"Under these reduced viewing conditions the fourteen subjects tended
to position the target at a slant regardless of its true orientation.
Errors of individual judgements were found to be very small and varied
in magnitude as a function of misperception. Results indicate that the
angle of rotation of the target is not the stimulus condition for the
perception or orientation. While position adjustment follows, in part,
the increments in visual angle associated with the horizontal expansion
of the target, this relationship breaks down and other changes appear
to be the more important cue. The fact that adjustments made under
the orderly sequence simulating rotation did not differ from those made
under random presentations indicated that memory or set was not a factor
in this adjustment."
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Martha J. Guastella
U. S. Naval Training Devices Center
Port Washington, New York
"The use of a varying picture plane model is presented as a hypothetical
construct to extend image transformation of the retina. The hypo-
thetical construct is used as a means for analyzing the changes in
retinal stimulation, taking into account changes in three dimensions.
A dynamic analysis involving the ratio of vertical and horizontal changes
in the boundary of the figure is used to predict the perceptual outcome.
Accounting for changes between true and apparent rotary movements, the
present theory permits analysis of illustory as well as nonillustory
visual experience."
The two papers above, taken together, provide a mathematical model to
describe certain illustory effects. A specific example of the Ames illusion,
in which a rotating trapezoid appears to oscillate back and forth instead,
was effectively demonstrated.
Sondra Wendroth and Edward Yose
Fairchild Space & Defense Systems
Syosset, L. I., New York
"The results in recent research in spectral zonal photography which have
resulted in the development of a Spectral Zonal Reconnaissance System
are discussed. This research has achieved a practical system based on
concepts of abridged spectrophotometry and calorimetry for photographing
the 3800 to 9500 Angstrom spectrum. Spectral zonal presentations of
terrain having the following characteristics will be shown:
1. Individual black and white spectral zonal image
2. Composite black and white panchromatic image
3. A true color composite image of the terrain
4. A color coded image presentation indicating disturbances to the
terrain such as camouflage
5. A color presentation allowing dynamic correction for atmospheric
haze, solar illumination and differences in the target spectral
reflectance
6. Spatial resolution equal to conventional reconnaissance camera
systems along with spectral discrimination
7. Minimized delay between taking photographs and viewing results
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"The chromatic accuracies obtainable from color aerial photographs taken
using the additive color principle is discussed.
"Additive color aerial photography is obtained by the simultaneous
imaging reflected electromagnetic radiation from the terrain through
selected filters on a suitable achromatic recording medium. When such
photographs are projected through compensating filters, the image is
seen in color.
"The accuracy of the color representation of the scene referenced to a
given standard is dependent on factors which include: filter-lens-
emulsion combination in the taking camera; accuracy with which the
characteristic curves of the individual photographs can be controlled
in processing; variations in the spectral quality of the scene
illuminant; the variable attenuation of the atmosphere.
"The relationship of object color in the scene to image color as viewed
by an observer will be presented in terms of C.I.E. chromaticity
coordinates.
"Compensations for chromatic inaccuracies in viewing due to the mentioned
effects can be partially adjusted for the entire scene by variation of
the hue, brightness and saturation of the image. The extent to which
this correction can be accomplished will be shown.
"The results of a series of experiments to determine the accuracy of
many classes of geographical characteristics are presented. Examples
of the chromatic differentiation of conditions of vigor of deciduous
foliage as well as certain classes of camouflage will be shown."
This paper on spectral zonal photography was well delivered but
described little that was new or unique in this field. Experimental
photographic camera and display systems of this nature were developed by
at least as early as 1959, followed by the nine-lens multiband camera, and
four-channel viewer/printer. Of course, "multiband photography," in the
form of three-color additive photography, stems from work performed by
James Clerk Maxwell near the turn of the century. In recent years a number
of industries, government agencies, and universities have become increasingly
interested in this type of photography. A very current example is the
three-band reconstruction of the color of the surface of the moon provided by
photographs from the Surveyor I spacecraft.
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1
The following abstract appeared in the program but was not delivered:
DISTORTIONS OF VISUAL SPACE
Gerald H. Fisher
Department of Psychology
University of Newcastle upon Tyne
England
"Before psychology emerged as an independent scientific discipline,
philosophers, physicists and physiologists became fascinated by some
remarkable and dramatic features of a rather unusual set of line
drawings. These drawings are composed of patterns of lines and shapes
juxtaposed in such a way that their configurations appear to be variously
distorted and attenuated. The addition of brackets, flaring in
opposite directions, to the ends of two lines of equal length, that they
appear to be of unequal lengths; a continuous oblique line, passing
across and apparently behind two parallel vertical lines, seems to be
discontinuous; while a simple cross in the shape of a plus sign, the
arms of which are exactly the same length, appears to be composed of
lines differing in length. The spatial distortions seen in these and
many other linear and curvilinear figures, have become known as the
?geometrical illusions.'
"There is a good deal of antipathy toward the study of the distortions
of visual space. The principal reason for this rests upon the claim
that, while spatial distortions are evident in abstract situations,
they are not seen when embodied within the concrete conditions of real
life. This argument has been considered in experiments embodying new
techniques for presentation of illusion figures in abstract and con-
crete, static and dynamic, and monocular and binocular situations.
"The results of these experiments suggest strongly that spatial
distortions are not confined to abstract situations but extend to
concrete, real-life conditions, the denotable physical characteristics
of which are such as to embody the spatial features of an illusion-
type display.
"In the context of the results of these and a variety of other experiments,
existing theories relevant to explaining aspects of shape and space
perception in general and to spatial distortions in particular, are
described and discussed critically. New principles are suggested which
appear to extend our understanding of the mechanisms underlying these
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distortions. It is concluded that no single element can account for
illustory-type spatial distortions but rather that, as in the case of a
general theory of space perception, a number of complementary and
frequently conflicting, perceptual systems are brought into operation
and must be invoked in order to explain the characteristic nature of
their perception."
SESSION IV
DECISION MAKING FROM IMAGE PRESENTATIONS
Session Chairman: Dr. Shelton MacLeod, RADC
A METHOD FOR RAPID HUMAN DECODING OF DIGITAL DATA RECORDED ON FILM
J. K. Libby
Fairchild Space & Defense Systems
Syossett, L. I., New York
"This paper describes a manual method for rapid human decoding of
digital data recorded on film. This method provides visual enhancement
of tiny digital data for more effective human decision making.
"The Department of Defense has directed the Army, Navy, Air Force and
Marine Corps to use the common reconnaissance mapping data marking
system established by MIL-STD-782B (Wep). All existing data marking
systems are to be converted to the binary-coded decimal system described
in this standard.
"The manual method provides a means for the photointerpreter to perform
relatively rapid, yet accurate decoding and recording of the binary
coded decimal (BCD) data. The tiny BCD bits are magnified by a rear
projection system so they are easily read and provide sufficient
spacing for rapid annotation of each character on a specifically
designed mask. This mask serves a dual purpose:
1) grouping the data bits functionally for rapid identification and
reading under all specified positions of the CMB;
2) providing a medium for recording the data being read which can be
reused or kept for record purposes.
"The compact projection system is designed for maximum light transmission
so that it can use existing diffused light sources. It is simply placed
over the tactical reconnaissance film being viewed on any direct viewing
light table."
t
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Richard Sweeton
Corporate Technology Center
Kollsman Instrument Corporation
Elmhurst, L. I., New York
"The decision maker referring to an image presentation must know the
degree of accuracy of the presentation or have blind faith that it is
accurate when he makes his decisions. This is particularly important
when he is making decisions where an error can result in deaths, as in
command control, or in a major economic loss to his company, as in
computer-aided management.
"Displayed information is generally referred to a map or chart grid or
to a prediction. The decisions then are essentially forced by the
displayed data moving off or across a line. If the display is mis-
registered with the reference line, errors are likely to occur. This
misregistration can be inherent to the display equipment, or it can
develop while the equipment is being used.
"In building projection display systems for command and control for
training, Kollsman has made accuracy analyses and has developed pro-
cedures for confirming system accuracy before depending on display.
New approaches are now being.studied for in-process checks on display
accuracy. This paper will cover types of display registration (spot
references, line reference, zone references); accuracy analysis tech-
niques; equipment factors affecting accuracy; and approaches to in-
process checks on accuracy."
James M. McKendry and Paul Harrison
HRB - Singer Inc.
State College, Pennsylvania
"A conceptual framework was proposed which summarizes a multitude of
specific activities which, when taken collectively, comprise a
significant portion of the image interpretation process. Usually,
these activities are either informally or formally organized into
sequences of behavior, guided by a desire to follow certain general
rules.
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"In this study, quantitative criterion data, based on user needs, were
obtained which permit derivation of clear image interpretation
strategies. If followed, the strategies should allow interpreters
to maximize the worth of their reports. The data are particularly
applicable to the task of interpreting ambiguous or incomplete imagery."
William R. Dyer
Interpretation and Analysis Section (EMIRC)
Reconnaissance Intelligence Data Handling Branch, USAF
Headquarters Rome ADC (AFSC), Griffiss AFB, New York
"This paper discusses measurement of image interpreter performance as
means for assessing techniques associated with proposed improvements
in reconnaissance technology (i.e., associated with the collection,
display, and processing of reconnaissance imagery). Selected examples
of research will be described to illustrate this approach including a
discussion of methodology for evaluating the contribution of color
imagery.
Joseph L. Hallett
Sylvania Electronic Systems
Sylvania Electric Products, Inc.
Needham Heights, Massachusetts
"Visual presentations, commonly called displays, overlap many engineering
disciplines. As a result, many different methods for measuring display
performance have been developed, depending on the background and
experience of the particular agency, company or individuals involved.
This paper is intended to highlight the problems of first obtaining a
workable definition of the end result desired from a given display, and
second, obtaining a workable method for rapid and accurate measurements
of the performance of individual components and equipment which must
eventually go together and satisfy the user's needs. Typically, the
user wants legibility and error-free performance, while the component
and system designer is more interested in such parameters as contrast,
brightness, color and resolution. To further complicate the problem,
the units and measurement techniques differ widely between different
engineering disciplines. Deficiencies in measuring equipment further
restrict both the user and the display designer from reaching quick
and easy conclusions about the performance of a particular display.
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The small lighted areas of most displayed data make some form of spot
photometer necessary to measure brightness; the monochromatic nature
of many displays makes most spot photometer measurements highly
questionable unless care has been taken to calibrate the instrument
on a standard source having the proper spectral energy distribution.
Contrast is considered to be important display parameter, yet the various
methods for establishing a known ambient illumination level can give
quite different numerical results. The human eye is extremely tolerant
of color and brightness changes, yet most display specifications are
quite rigid in controlling these parameters. It is hoped that the
discussion stimulated by these and other problems will help to establish
a climate where coordination of display measuring techniques and
standards will be accomplished."
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Page
B.1
PHYSIOLOGY
B-1
B.2
DUPLICITY (LUMINOUS EFFICIENCY)
B-10
B.3
ADAPTATION AND AFTERIMAGES
B-12
B.4
THRESHOLD
B-15
B.5
PERCEPTION
B-18
B.6
PERCEPTION - STEREO
B- 24
B.7
COLOR
B- 27
B.8
ACUITY
B-40
B.9
FLICKER
B-41
B.10
FATIGUE
B-43
B.11
INTERPRETATION OF COMPLEX IMAGES
B-45
B.12
MISCELLANEOUS AND GENERAL
B-51
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1. Yves Le Grand, Light, Color and Vision, London, Chapman and Hall, Ltd.,
1957.
Preface: point of view is essentially that of the physicist. Considers
eye as receptor of radiant energy. (Note: author has published, in French,
a first volume considering eye as optical instrument, and a third (1956) in
which two points of view are brought together. This English translation is
the second volume of three.)
No desire to ignore the physiological aspect, which alone can explain
the functioning of the retina and the nervous relays, but the accent is de-
finitely a physical one, and the aim is to give to opticians, to those who
construct visual apparatus, to illuminating engineers, architects, etc., as
much information and as many numerical data as possible concerning response
of eye to radiation.
This physical approach, purely experimental and stripped of all theory,
forms Section A of the book. Section B contains such elements of anatomy,
physiology and psychology as are necessary to understand the various visual
theories that have been suggested from time to time.
2. George Wald, "Eye and Camera," Scientific American, Vol. 183, No. 8,
August 1950.
The more we learn about mechanism of vision, the more pointed and
fruitful has become comparison with photography. Relation between eye and
camera goes far beyond simple optics, involves much of essential physics
and chemistry of both.
Each grain of silver bromide in exposed film blackens completely or not
at all; grain made susceptible to development by absorption of one or a few
quanta of light. Similarly, cone or rod is excited by light to yield maxi-
mal response or none. Absorption of quantum of light by light-sensitive
molecule in either structure might convert it into a biologic catalyst, or
enzyme, which could promote further reactions that discharge receptor cell.
Functionally, eye is one device in bright light and another in dim. In dim
light: ceases to adjust focus, resembles cheap fixed-focus camera. Vertebrate
eye is long-range high-acuity instrument, useless in short distances at which
insect compound eye resolves greatest detail.
Yellow color of lens and sensitivity shift toward higher wavelengths in
bright light compensate for chromatic aberration of eye, which is greatest in
blue and violet. Rods have max. sensitivity about 500 m?; cones 562. Also
fovea and region of retina around it are colored yellow in man, apes and
monkeys. Yellow patch removes for central retina the remaining regions of
spectrum for which color error is high.
Normal human color vision seems compounded of three kinds of responses.
Simplest assumption is that three light-sensitive pigments. In chicken and
turtle, oil globules in cones are three colors: red, orange, greenish-yellow.
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Bleaching of rhodopsin is composite process, ushered in by light reac-
tion that converts rhodopsin to highly unstable product; this decomposes by
chemical "dark" reactions that do not require light. As in photography,
light produces a latent image.
3. David H. Hubel, "Visual Cortex of the Brain," Scientific American,
Vol. 209, No. 5, November 1963, pp. 54-62.,
Transformation of retinal image into perception occurs partly in retina
but mostly in brain. Ten years ago Kuffler at J. Hopkins discovered that
some analysis of visual patterns takes place in nerve cells of retina. Now
Hubel and Wiesel at Harvard have mapped visual pathway to sixth step from
retina to cerebral cortex. Six types of nerve cells: three in retina, one
in geniculatebody (pair of cell clusters in brain), two in cortex.
Nerve cells on neurons transmit messages as electrochemical impulses.
In a given fiber all impulses have same amplitude; strength of stimulus re-
flected in frequency (1/2 to 100 m/sec). Fiber of nerve cell contacts
another, forming junction called synapse. At most synapses impulse releases
small amount of a specific substance, which diffuses outward to the membrane
of the next cell, where either excites or inhibits. For most synapses, sub-
stances that act as transmitters are unknown. Modification and analysis of
nerve messages takes place at synapses.
Studies of visual system of cat: record impulses with microelectrodes
in incoming and outgoing fibers, infer function of structures.
Receptor cells in retina do not send impulses directly through optic
nerve, but connect with retinal cells called bipolar cells. These connect
with retinal ganglion cells, which send optic nerve fibers to brain.
Receptor cells may send nerve endings to more than one bipolar; several
receptors may converge on one bipolar. Same for synapses between bipolar and
ganglion cells. Therefore, stimulating one receptor influences many bipolar
or ganglion cells; or one bipolar or ganglion may be influenced from a number
of receptors and hence from a large area of the retina. Any of synapses with
a particular cell may be excitatory or inhibitory: stimulation may either
increase or decrease cell's "firing rate." May receive several excitatory
and inhibitory impulses at once: responds according to net effect of inputs.
.Retinal ganglion cells fire at fairly steady rate even in absence of
stimulation. Kuffler: resting discharges of ganglion cells intensified or
diminished by light in small circular region of retina (cell's receptive
field). Depending wherein the field spot of light fell, firing rate in-
creased ("on" response) or decreased ("off" response). Turning light off
evoked burst of impulses. Two cell types among ganglions: small circular
"on" area surrounded by "off" area, or the reverse. Effect of liqht on a
given cell varied according to place where light struck field, for example,
two spots of light on separate parts of an "on" area produced more vigorous
"on" response than either spot along; if one on "on" and the other on "off,"
effects neutralized to very weak "on" or weak "off" response. Illuminating
entire central"orY region of an "on"-center cell evoked max response. Light-
ing up whole retina diffusely does not affect retinal ganglion cell so
strongly as small circular spot of right size to cover precisely the recep-
tive-field center. Main concern of these cells is contrast in illumination
between one retinal region and surrounding regions.
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Lateral geniculate body has function of increasing disparity between re-
sponses to small centered spot and to diffuse light, through greatly enhanced
capacity of periphery of geniculate cell's receptive field to cancel effects
of center.
Cerebral cortex. Most connections between cortical cells are perpendi-
cular to surface; arriving impulses probably exert effects quite locally.
Moreover, a given area of cortex gets input from a circumscribed area of re-
tina. Therefore a given cortical cell should have a small receptive field.
Cortical cells do not have concentric receptive fields: many different types
with fields different from retinal and geniculate cells. Two functional
groups of cortical cells: "simple" which respond to line stimuli (slits,
bars, edges)according to orientation and position on receptive field. "Com-
plex" cortical cells also respond best to bars, slits, edges, provided that
suitably oriented; but not so discriminating as to position of stimulus if
properly oriented. Complex cells respond with sustained firing to moving
lines.
From preference for specific orientation of stimuli, there must
be multiplicity of cortical cell types to handle all possible positions.
Wiesel & Hubel found large variety of responses but only studied hundreds of
individual cells (millions exist).
Simple cortical cells. Receptive field divided into "on" and "off"
areas. Not circularly symmetrical; typically, long narrow "on" area adjoined
on each side by larger "off" areas. Magnitude of response depends on how
much either type region covered by stimulating light. Slit of light just
filling long "on" region produces powerful "on" response. Slit in different
orientation, much weaker effect; right angles, usually completely ineffective.
Pitting of two antagonistic parts of receptive field is carried much farther
than it is in the lateral geniculate body. Large spot of light usually
evokes no response at all: "on" and "off" effects precisely balance out.
All arrangements of "on" and "off" areas have in common that borders
are straight parallel. Most efficient stimuli (slits, edges, bars) have
straight lines. Optimum orientation for each cell; if other than optimum,
less vigorous response, if perpendicular to optimum, usually no response. No
evidence that any one orientation more common than others.
Author supposes that simple cell has for input many lateral geniculate
cells whose "on" centers arranged along a straight line; spot of light any-
where along that line activates some of geniculate cells and leads to acti-
vation of cortical cells. Each simple cortical cell has specific duties:
takes care of one part of retina, responds best to one shape of stimulus and
to one orientation. For each stimulus -- area of retina, type of line,
orientation -- there is a particular set of simple cortical cells that will
respond.
Complex cortical cells. Respond best to line stimuli and must be ori-
ented to suit cell, but cannot be mapped into antagonistic "on" and "off"
regions. For example, in a typical complex cell, a vertical edge evoked re-
sponse anywhere within receptive field, "on" with light to left, "off" with
light to right. When stimulus is removed, without changing orientation, com-
plex cell responds with sustained firing. Continues as moved over substan-
tial retinal area, whereas simple cell only responds to movement as crosses
boundary between "on" and "off" regions. These findings can be explained by
supposition that a complex cell receives its input from many simple cells.
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Simples must have same field orientation and be of same general type, and
retinal positions of simple fields must be arranged throughout area occupied
by the complex field. This requires enormous degree of cortical organization.
Authors found evidence that such organization exists: arrangement of cortical
cells with high degree of order. Cortex divided into functional columns of
cells extending from surface to white matter. In each column, all cells have
same receptive-field orientation (from vertical microelectrode probe). In
respects other than orientation cells in a column differ: simple, complex,
respond to slits or bars or edges. Receptive fields vary randomly in exact
retinal positions, though all same general retinal region. Column is func-
tional unit in which simple cells receive connections from lateral geniculate
cells and send projections to complex cells.
Example, if looking at form such as black square on white background:
near edge of square will activate particular group of simple cells, which
prefer edges with light to left and dark to right and whose fields oriented
vertically and so placed that boundary betweeen "on" and "off" regions falls
exactly along image of near side of square. Other populations of cells acti-
vated by other three edges. Each edge also activates a population of com-
plex cells, but these continue,to be activated when eye or form moves. Thus
populations of complex cells affected by whole square will be to some extent
independent of exact position of image of square on retina.
Visual cortex analyzes enormous amount of information, with each small
region of visual field represented over and over in column after column,
first for one receptive field orientation and then for another. Cortex re-
arranges input from lateral geniculate body in a way that makes lines and
contours most important stimuli. First step in perceptual generalization re-
sults from response of cortical cells to orientation (apart from exact
retinal position) of stimulus. Movement also important stimulus factor.
Rate and direction must be specified if a cell is to be effectively driven.
If connections suggested by these studies are close to reality, can
conclude that at least some parts of brain can be followed relatively easily,
without requiring higher math,lcomputers, or knowledge of network theories.
4. W. H. Miller, F. Ratliff, and H. K. Hartline, "How Cells Receive Stimuli,
Scientific American, Vol. 205, No. 3, Sept. 1961, pp. 222-238.
In eyes of vertebrates no one has detected impulses in rods and cones.
Have been detected in optic nerve, which is composed of fibers of ganglion
cells separated from rods and cones by at least one group of nerve cells. In
any nerve fiber, impulses same magnitude, form, and speed; variation in in-
tensity of stimulus affects frequency of nerve impulses. Animals decode
sensory messages because each type of receptor communicates to higher nerve
centers through private set of nerve channels. Stimulation of receptor cells
appears to cause a sustained local depolarization of sensory nerve fiber,
which generates train of impulses ("generator potentials" at cellular level).
1935 generator potential found in single optic nerve fiber and receptor in
compound eye of horseshoe crab Limulus. 1950 demonstrated small steady de-
polarization in nerve fiber from vertebrate muscle spindle. Superimposed on
shifted signal (local potential) was a series of peaks representing indivi-.
dual nerve impulses. In steady state, frequency of impulses depends directly
on magnitude of altered potential. Local anesthetic: impulses abolished,
potential shift remains. Now abundant evidence that a receptor cell triggers
a train of nerve impulses by locally depolarizing the adjacent nerve fiber,
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its own or that of another cell. With sustained depolarizing current, re-
sponds briefly, then accommodates to stimulus. Only in photoreceptors have
we any knowledge of how stimulus produces generator potential. In work on
Limulus, site of origin of generator potential has not been identified with
certainty, nor has activity been detected in axons of retinular cells. In
photosensory cells alone, direct experimental evidence (through photochemis-
try) of initial molecular events in receptor process.
Visual receptor cells in both vertebrates and invertebrates have
specially differentiated organelles containing photosensitive pigment. In
vertebrates rhodopsin can be seen in outer segments of rods. Absorption
spectrum of human rhodopsin corresponds with light sensitivity curve for
human vision in dim light, when only rods operative. This is strong evidence
that rhodopsin brings about first active event in rod vision: absorption of
light by photoreceptor structure. Evidence for similar pigments in outer
segments of cones, but hard to isolate and study. Light absorbing part of
pigment is relatively simple substance, vitamin A aldehyde, which can exist
in various molecular configurations. Absorption of light changes configura-
tion; this leads, by unknown process, to initiation of generator potential of
receptor cell and discharge of impulses in optic nerve.
Intensity and duration of illumination (as in photography, shutter speed
and lens opening) can be interchanged, in human eye exposed to brief flashes
of light, to produce constant photochemical effect.
Flicker fusion: light flickering at high rate appears not to be flick-
ering at all. As demonstrated in Limulus, as repetition rate increases, rate
of impulse discharge becomes steadier and finally same as response to contin-
uous illumination. Flicker fusion is directly attributable to the generator
potential, which becomes smooth at highest repetition rates (see curves
p. 232).
Receptor cells of eye (ear and other organs) are interconnected neurally.
In Limulus, activity of each receptor unit is affected by adjacent activity:
frequency of impulses from a unit decreases when light falls on its neighbor.
Inhibition probably results from decrease in magnitude of generator potential
at site of origin of nerve impulses. When two adjacent units stimulated,
each discharges fewer impulses than when one receives same amount of light.
Visual effects of inhibitory interaction: differences in neural activ-
ity from differently lighted retinal regions are exaggerated, contrast is
heightened, and certain significant features of retinal image are accentuated
at the expense of fidelity of representation. Limulus ommatidium, with eye
masked so that only one unit "observed" pattern, faithfully reproduced form
of pattern. Eye unmasked so that all ommatidia observed pattern: frequency
increased on bright side of step pattern and decreased near dim side. Net
effect: outlines enhanced "border contrast" effect known and used in paint-
ing. Similar inhibition in auditory system would sharpen sense of pitch.
In many sense organs, responses can be modified by neural influences
exerted back onto them by higher nervous centers. Responses of eye and
other complex sense organs are determined by fundamental properties of re-
ceptor cells, influences they exert on one another, and control exerted on
them by other organs.
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5. Donald Kennedy, "Inhibition in Visual Systems," Scientific American,
Vol. 209, No. 1, July 1963, pp. 122-130.
In mammalian eyes, some single fibers of the optic nerve discharge im-
pulses when illumination of retina ceases. This signal is mediated by link-
age in circuitry of retina. Each fiber of optic nerve collects impulses from
a receptive field about 1 mm in diameter, containing several thousand recep-
tor cells. Activity generated in receptor cells converges, through inter-
mediate neurons called bipolar cells, on neurons that form optic nerve.
Kinds of connections depend on location in receptive field. In some fields
the center, when stimulated by light, produces discharges in optic nerve at
"on"; periphery produces discharges only when stimulus is extinguished, at
"off."
Interaction of retinal nerve cells blocks "on" discharges from some of
light receptors by inhibition at synaptic junctions between cells; the gener-
ation of "off" discharges in response to a shadow results from the release of
inhibition in these cells. This interaction plays a vital role in the per-
ception of movement across the visual field, in accentuation of contrast and
perception of shape.
Most of article devoted to inhibition in mollusk eyes (ability to see
shadows). Mollusks have played distinguished role in development of under-
standing of relation between photochemistry and visual response.
Photosensitivity may not be unique endowment of highly specialized re-
ceptor cells, but a much more basic property. (see urchin, crayfish)
Several kinds of excitable cells show "incidental" photosensitivity: heart
muscle of snails, muscle fibers in pupil of vertebrates, brain cells of some
insects, smooth-muscle cells from walls of arterioles in mammalian skin are
light sensitive. Ubiquity of this property may guide search for relations
between normal pigmented constituents of cells and events that lead to exci-
tation of nerve and muscle membranes.
6. L. J. & M. J. Milne, "Electrical Events in Vision," Scientific
American, Vol. 195, No. 6, Dec. 1956, pp. 113-122.
Information sent by eye to brain consists of electrical impulses arising
from eye's absorption of elementary quanta of light. In 19th century it was
demonstrated, by making electrical connection between outside eyeball and
retina., that eye, rather than reaction in brain, was responsible for ratio
of response to intensity of stimulus: size of voltage jump is proportional
to log of intensity, that is, to double electrical effect, light energy must
increase ten teimes (Weber-Fechner law, which applies to sensations in gen-
eral).
Now response of retina to light can be recorded with electronic ampli-
fiers, as electroretinogram. Since 1925 it has been possible to record
without removing the eye, that is, on human subjects.
Adaptation. Eye collects light as length of exposure increased, but has
threshold of intensity below which no lengthening will make visible. Experi-
ments on eye of horseshoe crab, compound eye,each unit of which has a separate
nerve fiber toward brain. Rate of impulse varies with dark-adaptation: gets
faster as exposure continues, then drops to a lower steady level. Thus dark
adaptation and other basic visual properties reside in individual receptor
cells.
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Cells are most sensitive to yellow-green, least to red, in all verte-
brates. Yellow-green is color which penetrates deepest into sea water;
sensitivity a heritage of evolution from aquatic life. Cones are compara-
tively blind to red, thus can use red for warning lights, instrument panels,
etc. without losing dark adaptation.
Threshold of visual response. Experiments on dark adapted subjects.
When saw 50% of flashes, amount of light arriving at eye was 150 quanta of
which thought 5-14 actually absorbed by sensitive cells. May have overesti-
mated absorptive quality; threshold may actually be 2-6 quanta. Thus eye
approaches ultimate in sensitivity.
Presumably each absorbed quantum of light energy alters one pigment
molecule. If two or three alteration produce a message, why not one? Brain
may dismiss one alteration, if not repeated, as insignificant.
7. Derek H. Fender, "Control Mechanisms of the Eye," Scientific American,
Vol. 211, No. 1, July 1964, pp. 24-33.
Article considers eye as servomechanism, or device that controls
variable physical quantity by comparing its actual value with a desired re-
ference value, using difference to adjust the variable.
Cone cells most closely packed in fovea, which is capable of sharpest
vision. For close examination, move eyes so that image falls on correspond-
ing areas of two foveas. Each of three pairs of rotating muscles receives
signals proportional to the displacement of image from the fovea. Another
control system brings eyes to correct angle of convergence; another adjusts
focus by changing thickness (focal length) of lens. Accommodation is not
"calculated" from angle of convergence but is achieved by a steady "hunting"
mechanism, like focusing a projector lens by hand, which continually shortens
and lengthens the focal length until accommodation has been steered to the
sharpest focus. Convergence and accommodation mechanisms are separate, but
cross-linked: information derived by one is fed to the other; for example,
information on sharpest focus fed across to convergence mechanism.
Another feedback mechanism changes diameter of pupil, linked to accom-
modative system because increase of focal length requires enlarged pupil to
keep brightness of image constant. Another circuit moves eyelids out of way
when looking up.
Rest of article devoted to records of eye movements in tracking moving
targets. (Eye moves even when staring at a fixed target, in a roughly
elliptical area of fixation, tilted because up-down muscles less precise
than across muscles.) Two distinct eye motions during fixation: slow drift
of visual axis, and sudden change of direction or "flick." Spontaneous
movement persist, i.e. eye has a lot of internal "noise." Spontaneous move-
ments must be eliminated in studies of tracking movements. Eye does not
travel as far as target, and lags behind it. When movement of target regular,
anticipates: an active element which allows it to calculate motion and lock
onto it. Prediction probably a function of cortex, but detection of objects
approaching from side may be built right into retina, because administering
of drugs does not suppress velocity signal for targets in periphery of visual
field, as does in fovea. Also image-displacement signal (that target is no
longer in fovea) is unaffected by drugs and is presumably retinal.
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Bipolar cells, amacrine cells, and ganglia in retina seem capable of
more than merely passing light signals on to brain: retinas discriminate
and filter information in lower animals, and presumably in higher, though
little known. Microscopic structure of retina is similar to brain: retina
is part of brain that became detached in course of evolution. Systems analy-
sis of retinal functions should therefore advance understanding of brain
functions.
8. Roy M. Pritchard, "Stabilized Images on the Retina," Scientific American,
Vol. 204, No. 6, June 1961, pp. 72-78.
Movements of eye when "fixated" on a stationary object: slow drift
away from center of fovea; this terminates in a flick which brings image back
toward center; in addition, a tremor, frequency up to 150 cps and amplitude
about 1/2 frequency of a single cone receptor. This motion plays significant
role in sensory functions: when an image stabilized, it soon fades and dis-
appears. Regenerates after time and becomes partly or completely visible;
over prolonged periods, alternately fades and regenerates.
This alternation is related to character and content of image. Evidence
from experiments at McGill U. suggests that pattern perception must be ex-
plained by reconciling "cell assembly" (learning is necessary to perceive
pattern, combining separate neural impressions in brain) and Gestalt (per-
ception is innately determined, perceived directly as whole without synthesis
of parts) theories. (cf Fantz 1961)
Image stabilized by attaching target to eyeball: contact lens, on which
mounted small optical projector, set on cornea and focused. After few se-
conds, image disappears progressively, leaving structureless gray field.
Simples figures such as lines vanish rapidly and reappear as complete images.
Complex images may vanish in fragments, parts fading independently. Time of
persistence of image is function of complexity.
Cell-assembly approach explains independence of parts as "perceptual
elements" established by experience. Meaningful elements remain visible
longer than unorganized ones. Gestalt: part independence also appears with
meaningless figures and can be explained by holistic perception. Continuity
and similarity strongly determine functioning of groups of images. Stimulus
excites perceptual response that goes beyond retinal region of actual stimu-
lation. Most stabilized figures are seen as three-dimensional. Color dis-
appears quickly from stabilized images, leaving,colorless field of different
brightnesses. Supports theory that perception of hue is maintained by con-
tinuous changes in luminosity of radiation falling on receptor. In other
words, movement of edges of a patch of color across the retina, produced by
normal eye movements, would be necessary for continuous perception of color.
Investigators are studying amplitude, frequency and form of movement neces-
sary to sustain or regenerate a particular color.
9. L. A. Riggs and S. U. Tulunay, "Visual Effects of Varying the Extent of
Compensation for Eye Movements," JOSA, Vol. 49, No. 8, Aug. 1959,
pp. 741-745.
Studies of visual effects of essentially motionless image on retina.
Devised a method, using contact lenses, whereby a retinal image did not
change its position despite eye movements: image reflected on screen, re-
tinal image moved through exactly same angular distance as eye. Elimination
of image motion caused disappearance of target, by a progressive washing out
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of contours. Contours could be restored by blinking or effecting large mo-
tion of eye, thus causing large variations of luminance with respect to re-
tinal receptors. Image can be restored to vision after disappearance of
image motion introduced in amount of 1 min of arc. (During attempted steady
fixation, eye normally wanders over about 10 min).
Retinal image of a straight line is imaged as blurred band of light
whose width determined by diffraction, optical aberrations, and scatter.
Under most favorable conditions, width of band is not less than about 38 sec
of arc. This means that any one cone receptor is not affected by full dif-
ference in luminance across a border until a motion of 38 sec or more has
occurred. With 10 percent error of stabilization this would require an eye
movement of 6.3 min of arc, somewhat larger than typical rapid saccades or
slow waves that are found during steady fixation.
Hartline has shown that a single ganglion cell axon in a vertebrate
retina can be stimulated by moving image of a line across retina. Very small
movements ineffective, but larger ones, that represent motions of 4 cone dia-
meters in visual field, arouse vigorous responses. These results are for
"off" and "on-off" types of fibers only; some fibers are capable of respond-
ing during steady illumination. Nevertheless, maintenance of vision probably
dependent on responses of those retinal units that are specialized for de-
tecting transient variations of the retinal image.
10. Hugh Davson, ed., The Eye, Vol. 2: The Visual Process, New York,
London, Academic Press, 1962.
Anterior chamber behind cornea (section of eye p.330) is filled with
aqueous humor of refractive index 1.33. Cornea and aqueous humor together
have refractive power of about 43 diopters, thus constituting the main re-
fractive surface of the eye.
(A 1-diopter lens has a focal length of 1 meter, a 10-diopter lens,
1 of 0.1 meter, and so on, diopter being the reciprocal of the focal length
in meters.)
Behind anterior chamber is lens, a double-convex body, the form and
hence refractive power of which can be varied by action of ciliary muscle.
The total power of the resting eye (when relaxed for distant vision) is about
60 diopters. In early life when lens soft and pliable a further 14 diopters
of power can be produced by max effort of ciliary muscle to accommodate
vision for near objects.
Refractive power of eye is not independent of wavelength: long w.l.
light refracted more than short. A human eye focused for 600 mi is about
1/2 diopter too strong for perfect focusing of 800 mi and about 2 diopters
too weak for perfect focusing of 400 m?. This chromatic aberration becomes
worse for shorter wavelengths. Thus axial aberration at 300 m4 is 6-7 diop-
ters. Inability to focus light of w.l. 300 mu, and lower limits use of these
wavelengths for vision: refracting eye (unlike compound eye) is only feebly
sensitive to these radiations.
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B.2 DUPLICITY (LUMINOUS EFFICIENCY)
Under natural conditions, daylight vision is largely mediated by cones,
night vision by rods. Best region of retina to be used is more eccentric
when illumination is lower; trained subjects can learn to use best retinal
region under given conditions.
In daylight, foveal vision gives highest acuity and normal eye sees
colors. Fixation reflex brings image of objects looked at onto fovea. At
illumination level of dark night, fovea is blind, only peripheral vision
operative, acuity much lower than in daylight and colors are not seen.
Recent study of directional sensitivity has given further support to
duplicity theory.
Purkinje phenomenon: relative brightness of objects appears to change
when general level of illumination altered (for example, in dim light, blue
objects look very much brighter than red). Because of different spectral
sensitivity of rods and cones: rods relatively more sensitive than cones to
blue end of spectrum. (This experiment works only,if eye adapted to low
illumination; otherwise neither red nor blue may be seen.)
Purkinje phenomenon may lead to considerable errors in visual measure-
ments expressed in photometric units. Only when relative spectral composi-
tion of two lights the same can visual photometry be used to equalize their
physical energies.
Light from night sky much richer in long wavelengths than daylight. Yet
differently colored objects still reflect light of different spectral compo-
sition, so color vision on dark night should not be physical impossibility.
Example: color photos in astronomy: study spectral composition of light
emitted by celestial bodies, "color" of which is never directly seen.
At very low illumination, eye becomes incapable of distinguishing be-
tween lights of different spectral composition, only differences seen being
those of brightness. Light too faint to stimulate cones; rod system only
functioning; this system incapable of responding in qualitatively different
manner to light of different wavelengths.
Why has rod system not developed powers of wavelength discrimination?
Probably connected with fact. that visual acuity becomes so poor on dark night
that wavelength discrimination would be of no biological value. Color of
small objects, or of details, is of significance, not color of sky or general
color of foliage. When small details can no longer be distinguished, color
vision loses its point. Also, quantum fluctuations would set limit to accur-
acy with which spectral distributions could be differentiated at low light
intensities, even if necessary physiological mechanisms existed. Even in
cone vision, confusions occur about subjective colored appearances of nearly
monochromatic stimuli of near-threshold intensity. Probably due at least
partly to-fluctuations in numbers of quanta acting on spectrally selective
cone mechanisms.
1
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Luminous efficiency of light ray entering eye is dependent on point in
pupil through which ray has passed. (Stiles-Crawford effect, disc. 1933.)`
Essentially a property of cones; for rods, directional effect absent or very
small for range of angles of incidence accessible through pupil. Before this,
generally supposed that apparent brightness of surface determined by total
flux of light entering pupil. However, now estimated that a given flux of
light entering through outer zones of pupil contributes less to apparent
brightness than equal flux entering near center. Near edges of (artificially
dilated) pupil, value of relative efficiency reduced to a third or even less
of what it is near center.
Explanation: for all positions of entry, rods are stimulated to same
extent, since they are almost non-directional. But cones in retinal area
receiving field image are less strongly stimulated for peripheral than for
central entry. Thus when peripheral entry used, provided field luminance
properly adjusted, cones are not stimulated at all, or stimulation insuf-
ficient to cause sensation of color. Colorless sensation received is medi-
ated through the rods.
Stiles-Crawford effect is valuable method of separating relative contri-
butions of rods and cones in many phenomena.
Magnitude of directional effect varies with wavelength. Change of color
in fovea of physically homogeneous radiation: Stiles-Crawford effect of the
second kind. Is distinct from intensity effect and might arise in a dif-
ferent way.
In extrafoveal test areas, large difference between curves at high and 0
field luminance. Those for bright field approximate in shape to foveal
curves; those for dark-adapted eye have almost flattened out, so that lumi-
nous efficiency of light pencil becomes almost independent of point of entry
through pupil. Foveal curves nearly same for high and 0 conditioning lumi-
nance, that is, pronounced directional sensitivity for both directions.
Weale (1961): varying thicknesses of eye lens, which contains yellow
pigment, may generate for light of short wavelength a difference between the
Stiles-Crawford effects as normally measured and the true retinal effect;
this would make the true retinal directional effect materially larger in the
blue than the measured effect. Rods may also have directional sensitivity
at short wavelength.
Cone vision can be isolated by confining stimulus to rod-free center of
fovea. There is no region of retina containing rods only; but rod vision
can be isolated to great extent by using low-light intensities with fully
dark-adapted eye, provided stimulus is not restricted to central part of
pupil. By peripheral entry, test stimulus in dark-adapted parafovea can be
made to act upon rods alone. For peripheral vision, using natural pupil,
there is an intermediate range of intensities where rods and peripheral cones
both appear to be active, and where luminous efficiency shifts from rod to
cone curve as intensity increased.
Range of low luminance levels ("scotopic") refers largely to rod func-
tion, intermediate ("mesopic") to combinations of rod and cone function.
Photopic range (daylight) refers to cone function, but when periphery used
in this range not clear whether rods are entirely out of action. Eye works
over total range of luminance of more than 1 to 1010.
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Retinal rods contain photosensitive substance "rhodopsin" which bleaches
under action of light. Strong dependence on wavelength of sensitivity of rod
system probably largely due to fact that rhodopsin absorbs some wavelengths
more readily than others. Absorbs max.in blue-green, where also max. sensi-
tivity; very little in deep red, where rod sensitivity is also low.
Absorption spectrum of human rhodopsin has been measured in vitro on
extracts. For purely optical reasons, shape of absorption spectrum of a sub-
stance varies with optical density (log to base 10 of ratio of intensity of
incident light by intensity transmitted) of the absorbing layer. Close cor-
respondence with rod quantum sensitivity at retinal level. This correspond-
ence sufficiently good to support theory of rod sensitivity curve. This was
very important when no pigments yet extracted from human cones. (See in-
fluence of wavelength on uncertainty of seeing.)Curves pp.75-76, max. about
500 m?.
Max. foveal sensitivity about 560 mu.; periphery about 507 (for 1-sec
flashes in dark-adapted eye). At foveal threshold, color of test field often
seen and varies with wavelength. For these conditions the fovea is less
sensitive than periphery except 675-740 m? where about same. With shorter
flash, 0.04 sec, cone vision favored because temporal summation smaller than
for rod vision. Here fovea becomes more sensitive than periphery about 600
Response of the fovea must be largely determined at any wavelength by
.the most sensitive cone mechanism for this wavelength. No evidence of genu-
ine physiological summation between cone mechanisms.
It would be completely wrong to think that the luminous efficiency of
radiation must always correspond either to the scotopic or to the photopic
function (p. 88).
B.3 ADAPTATION AND AFTERIMAGES
Page 94, typical curve for course of dark adaptation in near periphery.
At first threshold drops rapidly, then from about 5-7 minutes levels to
plateau. This first part of curve is cone branch. After cone-rod transition
time.(when appearance of white field changes from violet to colorless gray),
another less rapid drop; from about 15 min, change in threshold much slower,
after 25 min a further stay in the dark leads to little further change. This
second part of curve is rod branch. Under conditions of experiment, thres-
hold is about 10,000 times smaller at end than at beginning of dark adapta-
tion. Cone threshold is about 500 times higher than final rod threshold.
In case of fully dark-adapted periphery, both rods and cones become
active when submitted to intensities above cone threshold; rods most probably
out of action over extent of time covered by cone curve of dark-adapt experi-
ments. Important differences from one (presumably normal) subject to another
but general course of adaptation, especially the cone-rod transition time,
remains very similar from one subject to another. Individual final rod
thresholds cover range of 1 log unit, that is, lto 10.
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Prolonged exposure to sunlight produces temporary and cumulative effects
on night vision. After several hour:,e.g.,on beach, whole night of dark
adaptation is not sufficient to bring sensitivity to previous level. Several
days at lower illumination may be required.
When most of rhodopsin has been bleached in living human eye, it takes
about 1/2 hour to regenerate completely. Cone pigment takes only 7 min. to
regenerate. Some important link between regeneration of visual pigments and
that of dark adaptation. In normal subjects rod-cone transition time is
dark-adaptation time at which 90% of rhodopsin is present in rods, no matter
how extensive was initial bleaching..
Night vision: because of complex psychological factors which cannot be
reproduced in lab, visual performance in practice may be difficult to corre-
late with lab tests. Correlation may exist but fail to be detected because
of psychological variations.
Afterimages are the more obvious of the subjective phenomena which occur
when eye has been submitted to light stimuli. If eyes closed after looking
fixedly at light source or illuminated object, there is seen patch, size and
shape of which related to that of source: few seconds to several minutes,
or if very intense primary stimulus, may last for weeks. If looking at uni-
formly illuminated surface instead of closing eyes, afterimages are seen
which are darker than the surface ("negative afterimages").
Modes of appearance of afterimages do not obey hard and fast rules. If
colored source, positive afterimage may be same color as source, negative
afterimage of complementary color. But complicated color effects often ob-
served.
Conditions necessary for physically different stimuli to give indistin-
guishable afterimages (Brindley 1959). As increase in luminance, smallest
detectable difference increases. Afterimages of flashes of 1.5 x 106 and
1.5 x 107 cd.m 2 sec can no longer be distinguished from each other. These
two amounts of light are of the right order to correspond to bleaching of
the whole of the visual pigment contained in the retinal receptors receiving
the flash. Visually equivalent amounts of plane-polarized and unpolarized
lights produce indistinguishable afterimages. A fixed amount of light,
whether delivered during 0.02 sec or distributed over 2 sec, always produces
same afterimage, even though subjective effects of stimulus itself are very
different. This seems to suggest that the change responsible for after-
images is primarily a photochemical one.
Conditioned afterimages. Subjects made to hear sound when received
stimulation; then after hearing sound alone, without stimulus, they exper-
ienced afterimages. These illusions have something in common with those
experienced in absolute threshold experiments, when subject sees spurious
luminous patch on hearing shutter work, though light is cut off. This latter
illusion may be "dark noise" (spontaneous stimulation of receptor) but may
also be due to more complex neurophysiological processes.
Troxler phenomenon: progressive dimming and disappearance of illumi-
nated field, the image of which kept steadily on the retina. Generally
occurs with artificial stabilization of retinal images. In periphery, es-
pecially at scotopic luminances, readily observed with use of ordinary fix-
ation without artificial stabilization. Even in bright light, when fixation
maintained on one point, whole field of vision becomes progressively obscured.
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In experiments on dark-adapted eye with 50 field at 200 eccentricity,
ceased to see test field 5 to 10 sec after beginning of illumination. Whole
visual field then became uniformly dark except for fixation point. When
light-illuminating test field switched off, field reappeared momentarily as
a dark patch, darker than surrounding darkness. This may be due to excita-
tion of off-fibers in optic nerve. Time required for field to become invis-
ible remained constant for field luminances from absolute threshold to 1,000
times this. Bleaching of rhodopsinmust be negligible at these levels.
Phenomenon probably due to processes occurring in nervous connections of
retina or in visual pathways, independent of strength of stimulation at re-
ceptor level.
Common observation: eye is very poor at determining absolute levels of
luminance, whereas it can be very efficient at detecting differences of
luminance. A one-sec flash of luminance higher than 3 ft.-L (10 cd/m2) pre-
sented to dark-adapted eye looks brighter than steady field of 15,000 ft-L to
which eye has become fully adapted. Complex physiological processes seem to
be involved. Subjective brightness experienced during light-adaptation must
depend on eye movements, otherwise the adapting field should disappear alto-
gether.
13. G. S. Brindley, "Afterimages," Scientific American, Vol. 209, No. 4,
Oct. 1960, pp. 84-93.
Negative afterimages (seen against white background) presumably due to
insensitivity or "fatigue" of some part of the visual system, Caused by pre-
vious strong stimulation; positive afterimages (seen in darkness) to persis-
tence of stimulatory effects of bright light after it has ceased to shine.
Three mechanisms involved in reception of primary colors can be fatigued, and
can show persistent excitation, independently of each other. At least part
of fatigue responsible for negative afterimages occurs in eye and not in
brain (experienced while temporarily blinded due to loss of blood supply).
Bunsen-Roscoe law states that photochemical effects of any two light
stimuli are identical if products of strength and time of op. are equal. Eye
easily distinguishes between two stimuli, even if this is the case, therefore
two flashes must have different effects on nerve cells. Negative afterimages
of two flashes differ for first 15 seconds but after that are indistinguish-
able. This suggests that late neg afterimage of brief bright stimulus must
depend only on its photochemical effects.
In experiments, flashes above 100 units (candelas/m2 x sec) were dis-
criminated more readily by afterimages than immediate sensations. Fits hypo-
thesis of photochem origin. Total information regarding light intensity
capable of being received by pigments of retina is greater than the nerve
circuitry of visual pathway can transmit instantaneously; but can transmit
additional information later, in form of afterimage.
Flash of 1.5 mil units bleaches about 98% of green and red-sensitive
pigments of cones. Stronger only increased amount to 100%. Any pair of
flashes above 1.5 mil units produced indistinguishable afterimages. A single
very brief flash, however bright, cannot bleach more than half of a sample of
rhodopsin. Human cone pigments possess the same property. Photochem origin
of late neg afterimages may be either lack of receptive pigment in bleached
cones, or presence of some substance produced by the action of light on the
receptive pigment. Lack of pigment cannot explain progressive blurring.
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Chemical nature of diffusible products. Rod pigment rhodopsin, when
activated by light, splits into protein substance opsin, which remains fixed
in rods, and retinene 1, which can diffuse out of them. Iodopsin, only re-
ceptive cone pigment whose chemistry investigated, consists of retinene 1
combined with a different protein. Cone pigments chlorolabe and erythrolabe
may also be made up of retinene 1 and a specific protein, and be split by
light, yielding retinene 1 as diffusible product. But afterimage experienced
indicates that different diffusible products are liberated by light acting
on chlorolabe and erythrolabe; thus either not retinene 1 derivatives, or
diffusible substances responsible for afterimages are secondary products.
B.4 THRESHOLD
1
In chapter on "luminance difference thresholds": The idea of an absol-
ute threshold, or of a difference threshold, covers only one aspect of the
study of the visual receptor: it would clearly be absurd to consider condi-
tions of work in which the subject is kept close to the threshold; he would
tire very quickly and his performance would be lamentable. Many investiga-
tions have been carried out to establish the supra-liminal conditions
necessary in order to carry out a given task with comfort, but such work
falls outside the scope of the present book .(pp. 271-272).
Statistical definition. Threshold is not sharply defined on light
intensity scale. Thus is not possible to set apparatus at definite intensity
above which light always seen and below which never seen; range of uncertain
seeing varies with experimental conditions. This variation must be caused by
combination of biological variations and physical fluctuations in light sti-
mulus itself. Experimental threshold intensity must therefore be defined as
that intensity at which test field is seen with arbitrarily chosen % of ex-
posures, for example 50 or 55%. Value of 55% is convenient for theoretical
reasons.
Individual variations. In normal subjects under same conditions,
variations of statistically defined threshold occur from one subject to
another, and also in same subject from day to day, by as much as a factor of
two. These must be caused by long-term variations in properties of eye media,
retina, and visual pathway. Threshold tends to increase with age.
Statistically defined threshold values of different "normal" subjects
may differ by factor from 5 to 10. Night-blind subjects have much higher
threshold, but no subjects have thresholds very much lower than normal range.
Measurements discussed in this chapter 6 refer to presumably normal subjects,
periphery of dark-adapted eye.
Types of threshold measurement. (1) test field very large angular dia-
meter, presented in long exposures; this leads to lowest value of retinal
illumination necessary to cause a perception of light. (2) test field very
small angular diameter in long exposures; this leads to lowest value of total
radiant flux which must enter eye to make a light source visible. .(3) small
field presented in brief flashes, (e.g., 0.001 sec), with retinal position of
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image controlled by fixation point. When most sensitive region of retina
used, this method leads to smallest value of total amount of radiant energy
that can cause a visual sensation.
Hecht emphasized reliability of 3 subjects of main experiments, who did
not report as "seen" the blanks which introduced in random series of genuine
light flashes. Baumgartner used many blanks to study reliability: % of
blanks reported "seen" varied between 0 and 0.78% according to subject. Two
subjects who never reported blanks "seen" gave 55% threshold values between
85 and 114 quanta.
According to Barlow (1956) a subject can change his criterion of thres-
hold visibility from "seen" to "possibly seen," subject then reporting as
"possibly seen" 1% of the blanks, with result that statistically defined
threshold value becomes 25% lower.
To avoid influencing subject and responses in unpredictable ways,
flashes must be presented in random series of intensities unknown to subject.
(See following pages where opinion stated that false "seen" are cases
of conditioned afterimages, i.e., conditioned on sound of shutter.)
Assuming that uncertainty of seeing entirely determined by quantum
fluctuations: if probability of one subject seeing stimulus is 1/2, prob-
ability that one of two will see (with one eye each) is 3/4.
Similar results obtained for two eyes of one subject using brief small
flash in periphery. Probability of seeing when both eyes used follows steep-
er curve than probability for one eye only. Two eyes behave as if belonged
to two different persons; no evidence of either physical summation or inhib-
ition between them. Collier (1954),however,found binocular frequency of
seeing significantly greater than that computed from uniocular frequencies
on probability summation basis. This may be due to subject's criterion of
visibility being different in these experiments. May report flash as "seen"
when it is "barely seen" by both eyes.
Because of quantum properties of light, actual physical light stimulus
absorbed by retinal receptors varies from one trial to another, even when
all experimental conditions held constant. Smaller number of quanta, more
important the fluctuations.
Quantum theory states that any emission or absorption of radiation
takes place in a number of individual discrete events, in each of which a
single quantum exchanged. When studying quantum events we deal only with
probabilities, such as probability of absorption of a quantum by a given
retinal receptor. Under constant experimental conditions the mean number of
quanta absorbed by the rod, in many trials will be constant. But actual
number will vary and is impossible to predict for any given trial.
Amount of light of 507 mu equivalent to above amounts of white light can
be calculated from scotopic luminous efficiency function. Direct experi-
mental comparison with spectral band in green and with white light confirms
this calculation.
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At the 50% threshold, less than 0.3% of rods can on average be affected
by light during full 1/4 minute exposure; 99.7% fail to absorb even a single
quantum and are totally unaffected by stimulus. The large field is probably
seen when a few quanta have been absorbed in the receptive field of an optic
nerve fiber within summation time of this retinal functional unit; or stimu-
lation of more than one such unit may be required for threshold vision.
Quantum fluctuations will lead to random concentrations of quanta both in
space and time. For this reason, during 15 sec exposure, one or a few re-
tinal units receiving image may absorb within its summation time enough
quanta to be stimulated. Summating properties of all units involved are
insufficiently known to make accurate calculation possible. Subjectively,
large field near threshold looks blurred; subject cannot distinguish between
large luminous circle and each of component halves presented separately in
flashes.
Average absolute threshold for effectively point source emitting white
light and observations in extrafoveal vision with natural pupil, or order of
4 x 10-9 lumen/m2. Thus a source of one candela could be seen at distance of
order of 16 km if intervening medium perfectly transparent. Actual deter-
minations have given values ranging between 8 x 10-10 and 11 X 10-9 lumen/m2.
For flashes less than 0.1 sec for small fields, threshold energy content
of flash becomes minimal and independent of flash duration. According to
Ricco's Law a similar state of affairs exists for angular area of test field.
Thus small brief flashes of light of 507 m?, presented with help of fixation
point in most sensitive region of dark-adapted retina, make possible to de-
termine smallest quantity of radiant energy which must enter eye to make light
source visible. Experiment by Hecht: results for 7 subjects 54-148 quanta
of light for flashes seen in 60% of trials. For three subjects, five experi-
ments, 55% frequency of seening 9 - 143 quanta (safer values). These three
subjects did not report as "seen" the blanks which were introduced in random
series of genuine flashes.
If one rod were incapable of being stimulated by one quantum, there
would be no stimulation in 90% of flashes, whereas only 45% fail to be seen.
Therefore a retinal rod is capable of stimulation by absorption of a single
quantum. But absorption of quantum does not necessarily cause effective
stimulation in rod. Difference between effect of absorption of one and two
quanta is not known. One quantum is not sufficient to make human subject see
light stimulus. If area or duration of light stimulus is increased beyond
certain limits, mean total amount of light required for threshold vision be-
gins to increase considerably. This should not be so on hypothesis that one
quantum acting on rod is sufficient for seeing.
Interpretation of absolute threshold measurements in fovea much more
complex than in case of rod vision, since several cone mechanisms whose prop-
erties much less well known than those of rhodopsin. Foveal region, though
small, heterogeneous in its properties.
Stiles 1937 and Pirenne 1956: limit of perception of point source of
white light corresponds to illumination at eye of about 10-7 photopic lumen
per square meter for foveal vision. Light flux entering a 50 mm2 pupil is
then 5 X 10-12 lumen. Since measurements refer to cone vision, correction
for Stiles-Crawford effect is applicable; effective pupil area calculated to
be 24.6 mm2. Thus effective light flux which would be required for a small
central pupil is only 2.5 x 10-12 lumen. This would be equivalent to about
10,000 quanta (555 m?) per sec. These results refer to long exposures of the
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For an effectively point source the threshold values are higher for
cone than for rod vision, difference being greater for steady source than
for brief flash on account of greater range of temporal summation of rod.
For absolute parafoveal threshold, slope of frequency-of-seeing curve
almost same from 430 to 700 m?. This confirms interpretation of rod sensi-
tivity curve in chapter 4. For central entry, in which case cones are sti-
mulated at long wavelengths, slope increases beyond 550 m?, reaching value
of about 25 at 700 m?.
Pinegin (1958) found for given retinal position (in periphery) and
field size, slope of curve independent of wavelength. Riezler et al.,(1954)
found steeper curves for long and short wavelengths than for 505 m?. Prob-
lem seems worth investigating further with technique used by Flamant and
Stiles (1948).
Pinegin obtained steeper frequency-of-seeing curves for foveal than for
peripheral vision. Apparent number of acting quanta varied with field size
but not with wavelength.
B.5 PERCEPTION
16. John C. Eccles., "The Physiology of Imagination," Scientific American,
Vol. 199, No. 3, Sept. 1958, pp. 135-146.
Electric waves traveling on multilane pathways among the 10 billion
cells of cerebral cortex, correspond to the experience of mind.
Article explains transmission of wave fronts from sense organs to cor-
tex, including summation of impulses, crossing over, inhibition, etc. These
mechanisms explain brain waves made familiar by electroencephalography. In
inattentive but waking state predominating wave is 10 per sec. "alpha" rhy-
thm. To maintain even this low activity the cortex must be subject to con-
tinuous excitation by impulses from lower centers, or lapse into sleep.
When brain active, alpha waves give way to fast small irregular waves.
Visual experience brings barrage of impulses which disrupts tendency of
cortical neurons to settle into phased alpha rhythm. Concentration on
problem similarly stirs up heightened neuronal activity over large area of
cortex. Alpha waves relay high voltage: many neurons activated in phase;
negligibly small potential of fast waves suggests intense and finely pat-
terned activity.
Each type of sensory receptor activates neurons in narrow vertical
columns of cortex. Information from any sense organ must be capable of
integration with that from any other. Electric stimuli applied to sensory
zones of cortex evoke only chaotic sensations, since they excite tens of
thousands of neurons directly, regardless of their functional relations.
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Memory must be dependent on some enduring change in cortex due to pre-
vious activation, such as improvement in efficiency of synapse junctions.
May grow in size, or more transmission substance produced. Brain works as
patterned activity formed by curving and looping of wavefronts through many
neurons with speed deriving from millisecond relay time of individual neuron.
Tendency to association in imagery: cortex develops more complex and
effectively interlocked patterns of neuronal activity involving large frac-
tions of neuron population.
Different image-forming process involved in creative imagination. Pre-
requisites for creating activity of subconscious: in neuronal network must
be enormous development of highly complex engrams (permanent impressions left
on protoplasm) whose permanency derives from postulated increase of synaptic
efficacy. When great wealth of expert knowledge, engrams may occupy greater
part of cortex. Some failure in synthesis of engrams or conflict in rela-
tionship is neuronal counterpart of a problem to be solved. "Subconscious
operation of mind" involves intense and complex interplay of engrains. On
repeated activation, tends to be change in their congealed patterns result-
ing from interaction with other patterns. If an emergent pattern combines
and transcends existing patterns, may expect intensification of activity in
cortex which brings pattern to conscious attention.
17. Frank Barron, "The Psychology of Imagination," Scientific American,
Vol. 199, No. 3, Sept. 1958, pp. 150-156.
Average people dislike disorder; creative scientists and artists prefer
it, or prefer to impose their own higher order on apparent disorder: exp.
with figure preferences, drawing completion, word association, inkblots-.
Original scientists had preferences similar to those of artists; in art,
preferred works which accented usually unobserved aspects of nature, or
attempted radical reconstruction of world of common-sense reality. Behind
preference appears a very strong need to achieve the most difficult and
far-reaching ordering.
Average subjects disconcertingly ready to abandon evidence of their
senses, when contradicted, and bow to consensus. About 25% of subjects not
swayed by consensus, but persisted in giving correct answer. (Asch, Sci.
Am. Nov. 1955). Independence of judgment is linked to originality and to
preference for asymmetry. Creative people not "psychologically healthy" by
ordinary definitions (stability, friendliness, social responsibility). Need
another definition. Creative people, more at home with complexity and
apparent disorder than others, not only respect the irrational in themselves,
but court it as the most promising source,of novelty in thought. Charac-
teristics:
Especially observant and value accurate observations.
Often express part truths in order to stress the usually unobserved.
Independent in thought and will suffer pain to testify correctly.
Greater brain capacity; can cope with more ideas at once and make
richer synthesis.
More vigorous: large fund of psychic and physical energy.
Universe more complex and lead more complex lives.
More contact with life of unconscious: fantasy.,. reverie, imagination.
Broad and flexible awareness of selves.
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18. R. L. Fantz, "Origin of Form Perception," Scientific American, Vol. 204,
No. 5, May 1961, p. 66.
As well as seeing light, color, and movement, young infants respond
selectively to shape, pattern, size, and solidity. This behavior had al-
ready been demonstrated in chicks, which peck selectively at shapes resem-
bling grain, and in herring gulls, which prefer shapes resembling parent's
bill. Infants look consistently at some forms rather than others, so must
be able to perceive form. More complex forms draw greater attention--not a
result of learning process, since appears at all ages. Acuity of vision is
poor at birth and improves (width of stripes that could be distinguished).
Problem of learning: monkeys kept in dark from birth had to learn to
see. Complex interaction of innate ability, maturation, and learning in
development of visual behavior. There is a critical age for development of
given visual response, when visual, mental, and motor capacities are ready
to be used. If response is not "imprinted" at critical age for lack of
stimulus, development proceeds abnormally. At later age, experience and
training are needed to respond to stimulus.
Infants prefer face patterns: there is an unlearned primitive meaning
in form perception. Prefer solid objects.-- Interest in pattern is greater
than in color and brightness. Pattern is better guide to identification
under diverse conditions. Specific type of pattern, surface texture, pro-
vides orientation in space.
Interest in kinds of form that will later aid in object recognition,
social responsiveness and spatial orientation demonstrates innate knowledge
of environment.
19. N. Gattman and H. I, Kalish, "Experiments in Discrimination,"
Scientific American, Vol. 198, No. 1, Jan. 1958, pp. 77-82.
Stimulus generalization: a learned response to specific stimulus
carries over to whole class of similar stimuli. Hovland and others have
shown that there is a graded generalization of response to sounds and to
visual stimuli, declining with changes in pitch or in brightness or size of
object.
Pigeons trained to peck at light of given wavelength, responded in
regular pattern to different wavelengths, according to distance from sti-
mulus used in training. Curve of response crossed color boundaries without
abrupt drops. Birds recognize wavelengths entirely without reference to
color (? - non seq). Generalization and discrimination may therefore not
be simple opposites, as commonly supposed. (?) Training in discrimination
(between two wavelengths) enhanced response to new range; that is, shifted
peak response away from the negative stimulus. As response to conditioned
stimulus increased, resp. to associated stimuli increased in same ratio.
Stresses may heighten generalization and extend its range, that is, show
exaggerated reactions to stimuli which ordinarily would evoke no response.
In extreme case would react indiscriminately to virtually all stimuli in
environment.
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20. Ulric Neissen, "Visual Search," Scientific American, Vol. 210, No. 6,
June 1964, pp. 94-102.
Perceptual analysis seems to be carried out by many separate mechanisms
arranged in a hierarchy, the more complex receiving as their input the infor-
mation that has been assimilated and digested by more elementary ones. Exper-
iments with visual search at the boundary between perception and thought:
finding letters, words, numbers in lists. Some combination of feature-
detectors is presumably sufficient to penetrate the nervous system far enough
to stimulate activity in some subsystem sensitive to the letter that is
sought; activity suppressed for all other characters. Subject does not
identify that letters not sought, and cannot remember them when changed.
Multiple search does not take more time, so extra information must be
flowing in parallel rather than in increased depth. Many processes can be
carried out together (in contrast to intellectual thought, in which lose
efficiency) because of relatively low level of the cognitive analysis in-
volved in scanning. Achievements of newspaper clipping readers, who scan
for a thousand or so targets at once, confirm that speed of search is inde-
pendent of the number of different targets that can terminate it success-
fully. Cognitive operations involved are more than simply a search for com-
ponent letters (of a word sought) and less than full appreciation of the
meaning of each word scanned.
Subjects in tests began at different degrees of efficiency but in
letter-seeking tests leveled off at a common rate of about 10 lines per
second. With practice multiple targets could be found just as quickly as a
single target. Where the problem is to find a line that does not contain a
given letter, only about 4-5 lines per second.
Context of target is important, for example, the letter Z is quickly
found among round letters, but only slowly among angular ones.
Process of learning efficiency is variable and not considered in this
article.
21. Austin H. Riesen, "Arrested Vision," Scientific American, July 1950.
Depriving animals of patterned visual stimuli for period after birth
impairs their later visual performance, especially in form perception. Even
innate responses are affected.
22. Brian B. Boycott, "Learning in the Octopus," Scientific American,
Vol. 212, No. 3, March 1965, pp. 42-50.
Karl Lashley studied cerebral cortex of mammals. Concluded that in org
of a memory, involvement of specific groups of nerve cells is not as impor-
tant as the total number of nerve cells available for organization. At least
in the octopus's vertical lobe and mammalian cerebral cortex, memory is
everywhere and nowhere in particular (relation between amount of vertical
lobe left intact and accuracy of learned response).
Memory must consist not only of representation of learned situation, but
also a mechanism that enables the rep. to persist. In octopus, exp. demon-
strated a short-term memory which, by continuing activity between intervals
of training, leads to long-term change in brain. Epileptic patients with
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temporal lobes removed: man's cerebral cortex incorporates a long-term
memory system but hippocampal system (affected by surgery) is essential to
establishment of new long-term memories. Hipp. system may have function of
linking two memory mechanisms -- "whatever that may mean."
Evolution of memory: Young proposes that chemotactile and visual
centers developed from a primitive taste-and-bite reflex mechanism. More
indirect relation between change in environment and response. Signal
systems of longer duration than provided by simple reflex had to evolve:
learning had to become possible so that animal could assess significance of
distant environment change.
Lashley (Harvard): "I sometimes feel, in reviewing the evidence on the
localization of the memory trace, that the necessary conclusion is that
learning is just not possible."
23. Eckhard H. Hess, "Attitude and Pupil Size," Scientific American,
Vol. 212, No. 4, April 1965, pp. 46-54.
When shown interesting or attractive pictures, pupils of eyes dilate.
Response is a measure of interest, emotion, thought processes and attitudes.
Even overcomes the physical response to light, i..e.,when slide shown, every
part of screen brighter than before, so response ought to be negative: eye
should constrict slightly. Instead got positive responses that would have
been expected. Constriction occurred only for stimuli that person might
find unappealing.
Some stimuli, e.g.,pictures of battlefields, have strong shock content
and cause initial dilation; with repeated presentation, shift to constric-
tion. Time interval makes little difference.
Pupils dilate during mental activity, e.g., arithmetic problem solving.
Return to normal when subject gives answer to problem (not when solves).
24. W. C. H. Prentice, "Aftereffects in Perception," Scientific American,
Vol. 206, No. 1, Jan. 1962, pp. 44-49.
Experiments with reversible figures: cannot maintain orientation of
outlined cube or octagon with alternating dark and light sections. Some-
thing connected with initial way of seeing the figure becomes satiated.
First demonstrated through classical psychological methods, have been cor-
related with electrochem. changes in brain. Sensory stimulus produces
current flow through area of cerebral cortex to which stimulus related;
current satiates current-carrying capacity of that area, obstructs own
passage and diminishes. What experience at a given moment must be in some
ways a function of what has experienced in recent past.
W. Kohler, founder of Gestalt School, used reversible figures in study
of organization of visual patterns. Gibson (Smith & Cornell) studied nor-
malization of perceived world through learning. Aftereffects -- curving and
tilting of straight lines -- could not be explained as normalization.
Kohler: same mechanism "normalization" and reversal of experimental figures.
Figural aftereffects occur in depth as well as plane. Kohler proposed:
when impulses set up a sensory stimulus reaching nerve cells in appropriate
centers of cerebral cortex, activity of cells must generate direct currents
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through and around tissue. This must induce a state of polarization at cell
interfaces that increases the resistance of the tissue to the flow of cur-
rent. Conductivity and polarizability of tissue is changed and impulses
from later stimulation behave differently.
In visual perception, density of current would be greater in that part
of cortex associated with retinal image of figure's edge or contour. As
resistance builds up, flow of this current would be displaced to sections of
cortex in which tissues offer less resistance: those which correspond to
periphery rather than interior of object. If image of a new object now
falls on same place on retina, corresp. part of cortex is satiated and will
no longer react as it did initially: object appears distorted or displaced.
Simple to demonstrate that brain, not retina, is responsible for devel-
opment of figural aftereffects.
Even after Kohler had shown relevance of direct currents to psycholo-
gical findings, psychologists and physiologists continued to try to explain
without recourse to direct currents: proposed complex models of a brain
built with insulated pathways. 1946-52 Kohler and associates demonstrated
direct currents in human beings. Current generated by. moving stimulus. As
light moves across field of vision, a wave of potential change precedes it.
If moving stimulus stopped, potential difference between two electrodes (one
attached to skull over cortex, one grounded) drops to zero immediately.
Direct currents do flow through cortical tissue in response to stimu-
lation and do build up resistance to their own passage by changing electri-
cal properties of cortical tissue. Originally deduced from observation of
simple reversible figures. The world one sees at any one time must be de-
termined by what has seen in past. Much of "learning to see" is establish-
ing steady levels of satiation so that each new contour presented to eye
does not upset operation of visual system. Eyes move often and rapidly over
variety of objects: little tendency for satiation to build up in one por-
tion of cortex rather than others (but the reverse if staring at fixed
objects). Similar phenomena have been found in other senses.
Unwise to stare at fixed contours too long lest subsequent vision be
distorted; or to drive along straight highways, where eye continuously sti-
mulated by straight line of edge of road: affecting ability to judge dis-
tances on that side.
25. R. M. Pritchard, W. Heron and D. O. Hebb, "Visual Perception Approached
by the Method of Stabilized Images," Canadian Journal of Psychology,
Vol. 14, No. 2, pp. 67-77.
Stabilizing an image (by projecting from contact lens), thus eliminat-
ing involuntary eye movements, leads rapidly to disappearance of image,
followed by intermittent reappearance. Length of time line is visible as
function of thickness.
Meaningful diagram visible longer than meaningless. Straight line acts
as unit. Angles and corners not perceptual elements, as is stated elsewhere.
Evidence of functional meaning of "good" figure per Gestalt psychology;
of functioning of whole as perceptual entity; of groups as entities; of
similarity and continuity as determinants of grouping; marked field effects.
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But action of parts independent of whole tends to predominate over the
whole in way that never occurs in normal vision. Conclusion: the "wholes"
in question are simpler ones than usually discussed in Gestalt psych:
straight lines or short segments of curves. More complex wholes are synthe-
ses of simpler ones, though also function as genuine single entities.
26. Davson, op. cit.
Eye movements are necessary to counteract fading (which takes place
when image stabilized on retina) and the on/off play that is bound to take
place around contours or any other boundaries between different levels of
brightness must be formidable, to judge from the rapidity with which even
the cold-blooded frog eye responds when a pencil is drawn through a narrow
light beam focused on it.
With moderately good stabilization, colors become desaturated and per-
ception of form is impaired. With good stabilization the target becomes
gray and then dark. Normal vision can be restored by introducing controlled
movements or using flickering light.
All acts of visual discrimination are based on an interpretation of a
dynamic on/off pattern, an unstable image rather than a stopped one.
B.6 PERCEPTION - STEREO
27. Bela Julesz, "Texture and Visual Perception," Scientific American,
Vol. 212, No. 2, Feb. 1965, pp. 38-48.
Studied extent to which one can perceive differences in visual patterns
when all familiar cues removed, in order to dissociate primitive mechanisms
of perception from complex ones that depend on learned habits of recognition.
Questions: can two unfamiliar objects connected in space be distinguished
from differences in surface texture? Can two unfamiliar objects with identi-
cal surface texture be distinguished from separation in space?
Role of texture in discrimination. Random-dot patterns with different
properties were generated side by side. Might expect that texture discrimi-
nation governed by variations in statistical properties of patterns. (Why?)
Experiment showed that simple statistical measurements of brightness not
adequate to describe perceptual performance. Discrimination of texture in-
volves a kind of preprocessing: neighboring points with similar brightness
values are perceived as forming clusters of lines --"Connectivity detection."
Texture discrimination is really based on relatively simple statistics of
these clusters.
Spontaneous discrimination occurs even though two fields have same
average tonal quality, because granularity of fields is different. Nonspon-
taneous discrimination: two half fields of same apparent texture and granu-
larity, but one half forms English words, other, random sequences of letters.
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Visual system incorporates a slicer mechanism that separates adjacent
brightness levels into two broad categories of dark and light. Level of
slicing can be adjusted, but it is impossible to form clusters by shifting
our attention to dots that are not adjacent in brightness. Same connecti-
vity rules hold for patterns composed of dots of different colors adjusted
to have the same subjective brightness. Example: red-yellow field easily
distinguished from a blue-green, but red-green harder to distinguish from
blue-yellow. Dots of nonadjacent hue (red-green, blue-yellow) do not form
clusters.
Clustering of adjacent brightness levels or hues is important pre-
processing mechanism. When presented with complex patterns, visual system
does not perform statistical analysis but detects clusters and evaluates
only a few of their simpler properties. Objects can be distinguished by
differences in surface texture alone, even if spatially connected and cannot
be recognized. Texture discrimination depends on properties of clusters.
Cluster detection seems to be primitive and general process (frogs and cats).
Slit detector in cat's visual system is case of connectivity detection (?).
Spatial separation of objects. Computer generated random-dot patterns
identical except for a central area with parallax displacement. Could be
detected in stereo even when (1) one image blurred, (2) one image reduced
10%, (3) one image noisy. See illustration page 44. (But depth perception
of these imperfect pairs is also imperfect!) Stereo picture is devoid of
all familiarity and depth cues. This disproves a long-standing hypothesis
of depth perception, which assumes that the slightly different images pro-
jected onto the two retinas are first monocularly recognized and then
matched. Monocular recognition of shapes is unnecessary for depth per-
ception. Depth phenomena can be perceived in very short interval (a few
milliseconds presentation time). Depth perception must therefore occur at
some point in central nervous system after projected images have been fed
into a common neural pathway. But when long presentation time, convergence
motions of eye do influence depth perception. Processing in nervous system
that gives rise to depth perception is now more mystery than ever. Random-
dot stereo pairs actually easier to perceive in depth than images of real
objects. (?)
According to Gestalt psychology, stereo occurs as each eye works up
complex of stimuli into a Gestalt; difference between two G i's causes im-
pression of depth. With random-dot images no Gestalten can be worked up.
In image of raised square with fuzzy edges, black-and-white elements along
border have equal probability of being perceived as part of raised panel or
surrounding. Per G. psych. square (having good G.) would be perceived.
Subliminal perception of depth. Second pair flashed onto screen
immediately after first pair (original purpose, to erase afterimage). First
has panel unmistakably in front of or behind surround; second, panel ambi-
guous, may be either. With short interval between, subjects did not notice
first pair, which, however, influenced perception of second. When presen-
tation time of first pair long enough, ambiguous panel in second seemed at
same depth as in first. (40 milliseconds, the min. perception time for
stereopsis). All this processing must take place in central nervous system,
because times are too short for eye motion.
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Texture discrimination and depth perception operate under simpler
conditions than has been thought, since they do not require the recognition
of form. It is therefore feasible to design a machine for automatic pro-
duction of contour maps according to information in stereo aerial photos.
Connectivity detection is basic to both visual tasks, and is more primitive
process than form recognition.
Investigator's comments. At least a decade ago, photo interpreters
were perfectly aware that form recognition is not required for stereo. For
example, the tests of stereo perception published by Moessner required per-
ception of apparent height of individual dots (not even random patterns of
dots) above, on, or below the datum plane; and recognition of apparently
raised letters in a random array which formed a sentence when perceived in
stereo. Probably only psychologists were under the delusion that form rec-
ognition was important for stereo fusion, and that because they had mis-
applied Gestalt theory in a rather naive way. Author's "connectivity
detection" is likewise misapplied to the orientation preferences of the
cortical cells of cats (see Hubel 1963).
The examples of imperfect stereo pairs given in this article demon-
strate to the investigator that perception of such pairs is also imperfect.
The example with one blurred image causes an'interesting case of retinal
rivalry, in which blurred and sharp parts of the image are seen in distinct
pattern over the field.+ The out-of-scale and noisy images can be perceived
in stereo intermittently: the corners of the square drop off and reappear,
and usually only one edge can be seen in good steady stereo at one time.
Conditions like these, or viewers which present conditions like these (e.g.,
binocular "stereo" of different sets of photoqraphy, which differ in scale,
orientation, and sharpness) could hardly be recommended for photo interpreta
tion. (One wonders how his subjects reported their stereo impressions of
these examples. We all know that people sometimes rave about stereo when in
fact they see none, and that it takes some experience to notice and criti-
cize the quality of the stereo that one does see.)
The author has spent a great deal of experimental time belaboring the
obvious, and making questionable connections between his coined terms and
the controlled work of physiologists on neural pathways in anesthetized ani-
mals.
28. Eckhard H. Hess, "Shadows and Depth Perception," Scientific American,
Vol. 204, No. 3, March 1961, pp. 138-148.
Modern psychologists, as well as early investigators, tend to take view
that learning and experience are dominant in determining response to cues
of light and shadow. Some aspects of this faculty may depend on innate
mechanisms.
Human subjects interpreted image as in relief when presented "right
side up," and light as coinciding with angle at which picture tilted. If
picture in positions beyond 90 left or right of upright, most saw it in
intaglio but light source 180? from angle of tilt of picture. Assumed that
source of light above horizon, and impression of intaglio resulted from
continuing assumption.
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Experiments with chicks gave evidence that response to cue of light and
shadow is product of learning and experience. However, control chicks re-
sponded to cues sooner than experimental chicks: this leaves some ground
for arguing an innate preference for toplighted objects.
Some other types of visual depth perception, (e.g.., motion parallax),
seem to require innate mechanisms.
29. Ross H. Day, Brown University, Letter to Editor, Scientific American,
Vol. 205, No. 3, Sept. 1961.
Criticism of Ohwaki (Sci. Am, April 1961) who reports that well-known
geometrical illusions are minated or reduced in stereoscopic presentation.
This effect is, rather, explained by retinal rivalry, first observed by
Panum more than 100 years ago: that stimulus condition in which correspond-
ing retinal points are stimulated by different or "incompatible" patterns.
Alternation between patterns falling on each retina.
In figure of oblique and parallel lines, "test element" (parallel lines)
in view but "inducing" element (oblique lines) suppressed or inhibited.
Presented various figures stereoscopically and to one eye only. In
stereo, lines converging, or circular, across square wholly or partly sup-
pressed; observers saw bright square on field of fragmented lines or circles.
Square disappeared less often. Similar effects, with varying degrees of
rivalry, with several classical illusions.
For retinal rivalry, not necessary for two parts of figure to be super-
imposed. Less striking rivalry and suppression when test and inducing con-
tours merely impinge, or are slightly disparate. In stereo, the "inducing"
element is eliminated (by rivalry) from the pattern; therefore the illusory
effect not observed.
B.7 COLOR
30. W. A. H. Rushton, "Visual Pigments in Man," Scientific American,
Vol. 207, No. 5, Nov. 1962, pp. 120-132.
Reflectivity of backing of retina unchanging; rhodopsin lying in front
can be bleached away by strong light. If measure not color but intensity
of returning light, can find how much of incident light was absorbed by
rhodopsin. Experimental setup uses purple wedge to add the amount of purple
which matches that removed by bleaching. Wedge setting for constant photo-
cell output gives rhodopsin density at that moment. Rate of regeneration of
bleached rhodopsin follows exponential curve and is 90% complete in 15 min-
utes.
Field adaptation (quick change of sensitivity to large variable field,
such as cloudy sky), not dependent on amount of rhodopsin in rods, or visual
pigments in cones, but probably produced entirely by activity of nerve cells,
maintaining constant signal strength by exchanging sensitivity for space-
time discrimination. Adaptation of bleaching (from light room into dark) is
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tightly linked to level of rhodopsin. Field adaptation, rapid and uncon-
scious change of gain, makes absolute levels of light intensity hard to
judge. In judging brightness we estimate brightness of parts with respect
to mean brightness of whole.
Similarly, estimate color of parts of scene in relation to mean wave-
length of whole. Color perceptions surprisingly independent of wavelength
(Land experimented with two superimposed images made on b/w film through
different filters; appeared to contain a large range of color when one is
projected by red light and other by white). Eye uses average wavelength of
a red-white projection to judge color of parts.
Color matches remain good even in conditions of Land projections.
Maxwell showed that all colors could be matched by mixture of red, green,
blue primaries, and any three colors could be chosen as primaries provided
no one of them could be matched by mixture of other two. Trichromaticity
of color implies that cones have three pigments.
Color mixtures to match must deceive all three cone pigments at same
time. Matches depend on wavelength and intensity of light striking three
pigments, and on absorption spectra of three chemicals. Appearances are sub-
ject to whole complex of nervous interaction, not only between cone and cone
but also between sensation and preconception in mind.
Experiment with red-green blind persons: red-blind (protanope) to
measure green-sensitive pigment chlorolabe, and green-blind (deuteranope)
for red-sensitive erythrolabe. Spectral absorption of each coincides with
sensitivity. Person with normal color vision distinguishes colors in
red-orange-yellow-green range because each affects pigments erythrolabe and
chlorolabe in different proportions. Blue-sensitive pigment undoubtedly
exists, but harder to measure. Fovea is deficient in blue cones as well as
rods. Measurements in this area reveal properties of red and green only.
31. E. F. MacNichol, Jr., "Retinal Mechanisms of Color Vision," Vision
Research, Vol. 4, No. 1/2, June 1964, pp. 119-133.
Entire span of spectral colors can be matched by mixtures of lights of
any three primary wavelength bands. Problems: uniqueness of yellow sensa-
tion, no subjective mixtures of red-green or yellow-blue (but is a bluish
green). Many color sensations can be elicited with less than three primary
colors, especially when test object is complicated photographic scene (Land).
Analysis of pigment mixtures in solution by partial bleaching technique
has not yielded clear indication of different kinds of cone pigments in
higher vertebrates, although did distinguish cone pigment iodopsin from rod
pigment rhodopsin (Wald 1955). Hypothesis of single receptor acted on by
filters ruled out by showing that color matches could be made between light
entering normally through pupil and light entering from behind through
sclera.
Simplest way to distinguish between single- and multireceptor hypotheses
is to measure absorption or action spectra of photopigments in situ in single
receptors. Author and others constructed instrument sensitive enough to
measure absorption curves of small cones without irreparable distortion due
to bleaching. Data for 3 different cones from goldfish retinae: maximum
absorption by different receptors in 3 distinct regions of spectrum. This
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verifies Young's prediction of 3 kinds of receptors for at least one species
known to be capable of color discrimination. No significant data on humans
or other primates, whose foveal cones smaller and more difficult to measure.
Other type of measurement, direct but ambiguous information: micro-
electrode technique for recording electrical activity of single neurons.
All that can be said at present about mechanism of excitation and conduction
in vertebrate photoreceptors is that very little known about it and it pre-
sents a real challenge to investigators. Color-related electrical activity
has been found (S-potentials) in fish retinae.
C-responses in fish retinae appear to be signs of definite color dis-
crimination which is reminiscent of Hering opponent color hypothesis. In
mullet, 2 kinds of C-response, a red-green and a blue-yellow opponent pair.
In goldfish, units have been found that gave on-responses in long wavelength
region and off-response in short; other units, opposite. Author has tended
to regard off-response as post-inhibitory rebound phenomenon which may serve
to accentuate termination of inhibitory stimulus. It is clear that in gold-
fish (at least) wavelength information is carried up optic nerve in form of
discharges of axons of a population of ganglion cells which are acted upon
by groups of receptors having sensitivities in different parts of spectrum.
At level of S-potential, and later at level of optic nerve fiber
discharge, elements that behave consistently with Hering's red-green, blue-
yellow, black-white processes. But these elements are in animals which have
been shown to have 3 kinds of cones maximally sensitive in 3 spectral re-
gions. Thus a retina may be consistent with Young theory at receptor cell
level and with Hering theory at level of optic nerve fibers.
Not certain that same mechanisms operate in primates, but investiga-
tions which indicate that retinal mechanisms in fish, monkey and man are not
likely to differ very greatly.
32. Davson, op. cit.
Wavelength discrimination. Neurophysiology is not concerned with
color vision. Its task is to study and analyze mechanisms of wavelength
discrimination. Some results may lend themselves to theoretical inter-
pretation in terms of visual experience or behavior reactions to light.
Other (results) are parts of a complex organization for transmitting infor-
mation to the brain, and cannot be so interpreted. Moreover, psychological
phenomena of color vision belong to sphere of experience more limited than
electrophysiological studies of whole vertebrate kingdom. Even man him-
self may use only a fraction of whole visual input for building up his world
of color. We should be careful not to force psychological interpretations
on everything that we can record, knowing as we do that the vestibular
control of the gaze is wholly automatic (p. 577).
Color vision belongs to another conceptual world, that of psychology.
Assumption that wavelength discrimination must necessarily lead to "color
vision" can only be entertained in the modified version that retinal mech-
anisms of wavelength discrimination in some instances also have been made
use of to support perception of color. For this reason the neurophysiolo-
gist may be interested in considering what his results might mean for
understanding of the psychophysical results referring to color vision
(p. 639).
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From Hubel and Wiesel's work we are compelled to come to the conclusion
that there can be no evoked potentials to diffuse illumination. (Writer
thinks their results contain an unknown "x" of selection.) This is strangely
reminiscent of situation in which behaviorists conclude from their experi-
ments on "color vision" that the cat can have no discrimination of wave-
length (p. 753).
Spectrum consists of continuous range of colors and limits given (on
p. 224) are only approximate. Different observers give different names to
monochromatic lights: for example, 500 mp, may be called blue by one observer
and green by another. Ends of spectrum not clearly defined; intense radia-
tion of w.l. greater than 700 mp. can be seen as deep red light. Light of
very long w.l. is not uniform in color. Under suitable conditions UV can
be detected down to 315.5 m?.
Eye does not analyze light into components, as ear analyzes sound.
Totally different mixtures of monochromatic lights may appear identical.
Color perception not an analytical process like the use of a spectroscope.
Confusions, or color matches, give much of information from which processes
of vision can be inferred.
Dominant wavelength and colorimetric purity of a stimulus together de-
fine its chromaticity, that is, its color quality without reference to
brightness. Two colors when mixed in suitable proportions produce white are
termed complementary: red and blue-green, orange and blue, yellow and blue
of shorter w.l. Green w.l.'s have no spectral complementary, but form white
with suitably chosen purple lights. If three primaries are chosen, say in
red, green, and blue portions of spectrum, then any other light can be used
to form a match with the three primaries.
Discrimination. In practice, experimental work has been largely con-
fined to intensity discrimination for lights of similar spectral composition,
and chromaticity discrimination for lights of equal intensity. Least per-
ceptible difference between 2 lights depends on number of factors, such as
field size, intensity, and criterion adopted for discrimination.
Chromaticity discrimination depends on w.l. values. Near limits of
spectrum, especially in deep red, large differences in w.l. make no percep-
tible difference to color of light; near center of visible spectrum, w.l.
difference of as little as 1 m? can be detected. Best in blue-green and
orange-yellow, with secondary minimum in violet-blue (curve p. 275).
Near ends of spectrum, where w.l. discrimination least accurate, re-
latively small change in purity (add mixture"of white light with adjustment of
luminosity) can be detected, whereas in green, where w.l. discrimination is
good, larger addition of white light needed before change in purity detected.
Intensity discrimination in foveal vision, when only cones active,
Weber fraction becomes constant for all intensities above a certain level and
is independent of color of light. Since all colored lights affect the three
mechanisms, differences in intensity, except at very low levels, are detected
by whichever mechanism has the lowest Weber fraction, and the high value of
the blue mechanism does not raise the value of Weber fraction for blue lights.
Low intensities. At very low intensities, color discrimination becomes
poor and only a few shades can be distinguished. For many colored lights,
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including spectral lights, there is no color sensation at all even at inten-
sities well above threshold for perception of light. Interval between thres-
hold of light perception and level at which color can be recognized is
photochromatic interval. This interval must always be defined with reference
to the conditions of viewing. When light seen in brief flashes of near
threshold intensity, color recognition is especially bad. Green lights may appear
green, white, or red. Red lights sometimes appear colorless, but never any
other color. Color confusions attributed to quantum effects. If only a few
quanta needed to stimulate a color mechanism, and if difference in sensiti-
vity between two mechanisms is not very great at the wavelength used, the
"wrong" mechanism may by chance be more strongly stimulated than the "right"
one.
Bezold-Brucke effect. At high luminances, spectral lights change
apparent color. Red and green lights look more yellowish; blue-green and
violet look blue. On Young theory a deep red light acts most strongly on red
mechanism, less on green. For very bright lights, red mechanism approaches
saturation and does-not respond so strongly to further increases in intensity.
Relative increase in response of green mechanism, which is far from satura-
tion, is accordingly stronger and apparent alteration of color toward yellow.
Similar but less striking variation in apparent hue at low intensities near
color threshold. Similarly explicable as difference in gradients of response
curves of mechanisms when one of them close to its threshold.
Contrast'effects. After adaptation to colored light, white light ap-
pears to have hue complementary to adapting light. Successive contrast, due
to adaptation of mechanism affected by adapting light. Also apparent when
colored light viewed after adaptation. Simultaneous contrast: any color
placed next to another tends to appear like complementary of adjacent color,
thus subjective exaggeration of physical contrast between adjacent colors.
When whole scene illuminated by colored light, tendency to ignore the general
coloration and "correct" apparent colors of objects. Land experiments depend
on combination of "correcting" effect with simultaneous contrast. Photos
taken through red and green filters projected on screen using red and white
light. General reddening of image largely unnoticed, and parts of screen lit
only by white light (corresponding to green and blue objects in original
scene) appeared by contrast blue-green.
Simultaneous contrast is explained in the same way as successive
contrast -- selective inhibition of one or two of the color mechanisms -- if
it is assumed that there can be lateral spread of inhibitory effects across
retina. Pirenne (1958) has made psychophysical experiments giving strong
evidence of existence of lateral inhibitory effects in human rod vision.
Simplest hypothesis which fits facts of color matching is that there are
just 3 photosensitive pigments used for color vision contained in three types
of retinal cone. The various transformations that may take place in the ner-
vous pathways to the visual cortex are not involved in the (tri-receptor)
theory.
Response curves of different types of cone are not reflected in response
curves of all nerve cells in visual pathway. There is "recoding" of receptor
response, which may be transmitted in different forms at different stages of
the visual pathway. Theories that attempt to give an account of form of res-
ponse at different stages are known as "zone" or "stage" theories. Such
theories cannot be validly based on subjective phenomena alone. Must rely on
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electrophysiological or histological results. Zone theories at-present are
based more on intuition than experimental fact.
Opponent-color theory, after Hering, offers only the most nebulous ad-
vantages over classical Young theory, and has several grave disadvantages:
greater complexity, failure to explain protanopia, and lack of support from
electrophysiology. Main reason for its continued existence is confusion of
terms.
33. George Wald, "The Receptors of Human Color Vision," Science, Vol. 145,
No. 3636, Sept. 4, 1964, pp.. 1007-1017.
Determination of s ectral sensitivities of 3 types of cone must be
approached directly: there is no unique theoretical solution: an infinite
array of hypothetical trios of spectral sensitivity functions, all inter-
convertible by linear transformations, can satisfy the formal demands of
most color-vision measurements.
Experiments on crayfish, which possesses apparatus suitable for color
vision: at least two visual pigments segregated in different receptors and
poised at about same level of sensitivity. Sensitivity throughout spectrum
measured in dark-adapted eye. Then one type of receptor selectively adapted
to colored light, and redetermination of visual thresholds throughout spec-
trum revealed spectral sensitivity of other type of receptor. For example,
with eye continuously adapted to red light, spectral sensitivity measured
was that of the blue-receptor. Response of each type of receptor not at all
distorted by such background adaptations. Such invariance with conditions of
adaptation is an essentially photochemical criterion, characterizing the
activity of a single visual pigment. (This is not necessarily the criterion
for isolating a single receptor type, e.g.,a cone. A cone containing a mix-
ture of pigments would change in spectral sensitivity with color of adapting
light.)
This article reports same type of procedure applied to human eye.
When fovea continuously adapted to bright yellow light, spectral sensi-
tivity curve is that of blue receptor: high narrow band max. at about 435-440.
Simultaneous adaptation to wave bands in blue and red (purple light) isolates
green receptor: max at about 550 with broad shoulder in blue (an extraneous
effect). Adaptation to blue light isolates red receptor. Max about 580-585.
Curves for green- and red-receptors overlap widely and may be too much to
expect absolute isolations.
Curves corrected to give spectral sensitivity at level of cones,that is,
eliminate distortion from filtering action of yellow structures, max at 430,
540, 575 m?. Unlike corneal sensitivity curves, corrected curves for two
subjects are invariant.
Ocular and macular absorptions. Spectral sensitivity curves, measured
in terms of light incident on surface of cornea, are distorted (relative to
intrinsic properties of visual pigments) by filtering action of colored
structures in eye. These are principally the yellow lens and yellow pig-
mentation of macula lutea.
Individual differences. Two subjects had relatively high foveal sensi-
tivity in blue, apparently caused by greater than average amount of blue-re-
ceptor. Appears to be genetically determined. Another subject with lower
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than average sensitivity toward violet end of spectrum, probably has denser
ocular and macular pigmentation than average. Data for these subjects cor-
rected accordingly.
Beyond 650 m? red-receptor accounts entirely for total sensitivity and
hue discrimination ceases. If blue- and green-sensitive cones contained
red-sensitive pigment they should still function at long wavelengths.
Yellow lights used to isolate spectral sensitivity of blue-receptor cause so
little adaptation in violet that seems unlikely that blue-sensitive cones
contain appreciable amounts of other pigments. Possibility still remains
that red-sensitive cones contain mixtures of pigments.
Blue or violet as primary sensation. This distinction has plagued color
vision theory since beginning. Young, Hemlmoltz and author chose violet;
common practice at present is to consider blue primary.
Color blindness. (discussion p. 1015 ff.) Color blindness includes not
three but four main types, and indeed two different kinds of "deuteranope."
One kind lacks green-sensitive pigment and is literally green-blind; other
has all three pigments in normal proportions but red and green mechanisms are
coupled to form single sensory system. This distinction is fundamental to
understanding of subject. If second kind of deuteranope see long w.l.'s as
yellow as has been reported, may also possess all three sensory mechanisms
and their disability is a confusion of red and green pathways so that both
red- and green-sensitive pigments excite both pathways indiscriminately and
evoke yellow sensation.
34. T. N. Cornsweet, H. Fowler, R. G. Rabedeau, R. E. Whalen, and D. R.
Williams, "Changes in the Perceived Color of Very Bright Stimuli,"
Science, Vol. 128, No. 3329, Oct. 17, 1958, pp. 898-899.
When very intense stimuli in long wavelength region of visual spectrum
are viewed continuously, they change in hue from red through yellow to green.
Time course of change is related to intensity of stimulus.
Intense yellow stimuli at wavelength of 575 mu. (found by Purdy to be
"invariant") also changed to green. Green stimuli desaturate but do not turn
red.
May be explained by photochemical adaptation, if assumed there are at
least two photopigments, a red and a green with overlapping absorption
spectra, and that rate of regeneration of green is slightly greater than that
of red.
35. Harry Helson, "Some Factors and Implications of Color Constancy," JOSA,
Vol. 33, No. 10, Oct. 1943, pp. 555-567.
Colors and forms tend within limits to remain constant in spite of
change in illumination and orientation. Problem of color constancy involves
not one but many aspects of vision including spatial functions of eye. How-
ever, nothing like complete preservation of all color dimensions is found
under changing conditions: at best only one or two dimensions remain stable
while others change. Surface colors approximate various degrees of con-
stancy while colors seen through aperture maintain closer correspondence
with actual stimulus impinging on retina. But aperture colors are no less
subject to influence from the aperture screen than surface colors to sur-
roundings.
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Animals below man show constancy tendencies as strong as man. Higher
psychological functions are, therefore, not involved.
Limits of compensation. Radical change in composition of illumination
from daylight (e.g.,spectrally homogeneous light) greatly alters relations
between fundamental dimensions of colors. Breakdown in constancy also oc-
curs when objects viewed at a distance: yellow appears red, then orange,
then yellow; violet appears blue, then brown, then black, then violet, with
increasing distance. Once limits of compensation reached, color changes
from common experience are many and baffling.
Visual mechanism behaves as if it had different sensitivities for dif-
ferent dimensions (Land). Eye is least sensitive to change in general illum-
ination. Wide range of reflectances can yield black, gray, or white, depend-
ing on reflectance of background.
Author regards visual mechanism as unitary mechanism with extraordinary
adaptability of function.
Contrast is establishment of gradients, not with respect to reflectances
of contiguous surfaces, but with respect to adaptation level which tends to
be intermediate between these reflectances. Color compensation occurs for
different reasons, but springing from a single source.
Colors also have inherent spatial properties, inseparable from contour
and boundary effects and just as important for organization of the visual
field. Color processes not only contribute the matter of visual field, but
also determine the way in which the field is organized both bi- and tridi-
mensionally. Which is to be regarded as primary, color or space, is too
early to decide, but evidence points to increasing recognition of importance
of color for spatial discriminations.
Cold colors, weak chromas, values near background value, soft edges,
dark objects with blue edges, all appear more distant than the reverse.
Hard colors (red, yellow, white) have greater organizing power than soft
colors (green, blue, black). Hard colors on hard grounds give greater visual
acuity than soft colors on soft ground.
Color compensation, by yielding approximate color constancy, thus aids
in the production of a stable visual world, not only through preservation of
color as such but just as much through preservation of spatial organization
which is largely due to the color processes of the eye.
36. Edwin H. Land, "Experiments in Color Vision," Scientific American,
Vol. 200, No. 5, May 1959, pp. 84-99.
Work on natural color images (rather than matching spots of light).
Photograph natural scene through two filters that pass different bands; used
red and green filters. When transparencies are illuminated with practically
any pair of wavelengths, and images are superimposed, colored images are
obtained. If sending longer of two through long-wave (red) photograph and
shorter through short-wave photo, obtain most or all of colors in original
scene. If reverse process, colors reverse: reds appear as blue-greens, etc.
Colors in images arise not from choice of wavelength but from interplay
of longer and shorter wavelengths over entire scene.
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Width of band makes little difference: one may be as wide as entire
visible spectrum (white light). If use red for long record and white for
short, colors look about same to color film as they do to the eye. Colors
hold fast through very considerable range of light intensities.
Evidently, though eye needs different brightness ratios, distributed
over different parts of the image, to perceive color, ratios that eye is
interested in are not simple arithmetic ones. Somehow they involve the
entire field of view.
There must be a minimum separation between the long-record wavelength
and the short. Minimum is different for different parts of spectrum, but is
astonishingly small. Any pair of wavelengths far enough apart will produce
grays and white plus gamut of colors extending well beyond that expected
classically from the stimulating wavelengths, including nonspectral color
sensations such as brown and purple. With some pairs colors maintained over
enormous range of brightness; with others, begin to break down with smaller
changes.
Author has formed coordinate system that predicts colors that will be
seen in natural images. If put same transparency in both projectors, all
points would fall on gray line, since % of available light is the same at
every point on image for both projectors. Other colors arrange themselves
in a systematic way about the 45-degree line. Warm colors above, cool
below. Significant scale of color for images is not spectrum arrangement,
but runs from warm colors through neutral colors to cool colors. (see
graphs p. 89) For every pair of wavelengths that produce full color,
position of colors on graph remains same.
Colors in a natural image are determined by relative balance of long
and short wavelengths over entire scene, assuming that relationship changes
in somewhat random way from point to point. Within broad limits, actual
values of wavelengths makes no difference, nor does overall available
brightness of each.
Eye is not only adapted to see color in world of light in which it has
evolved, but also can respond with a full range of sensation in much more
limited worlds. If could find pigments with much narrower response curves,
might provide full color in a more restricted world of light - for example,
a world lighted by wavelengths that pass green filter. A two-color separa-
tion photo in a world of any bandwidth is same as a two-color photo in a
world of any other bandwidth, provided that a correctly proportioned change
in absorption bandsof pigments goes along with it.
If eye perceives color by comparing longer and shorter wavelengths,
must establish a balance point or fulcrum on one side of which all wave-
lengths are taken as long and on other side as short. In ordinary sunlight
world fulcrum appears to be at 588 m? ("yellow"). When use 588 in one pro-
jector, white light in other, image nearly colorless. With length shorter
than 588, white serves as longer stimulus; with length longer than 588,
white becomes the short record.
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37. Deane B. Judd, "Appraisal of Land's Work on Two-Primary Color
Projections," JOSA, Vol. 50, No. 3, March 1960, pp. 254-268.
No new theory is required for the prediction of Land's result that
two-primary color projections can produce object-color perceptions of all
hues, nor for his result that many choices of pairs of primaries yield sub-
stantially the same object-color perceptions. Land's hypothesis that when
colors of patches of light making up a scene are restricted to a one-dimen-
sional variation of any sort, the observer usually perceives the objects in
that scene as essentially without hue, is new. Several special cases of it
are supported by previous work as well as Land's. This hypothesis deserves
the serious attention of research workers in object-color perception.
"Classical expectation" of good correlation between color of light
patch and perception of color viewed against dark surround applies to aper-
ture mode of perception. This condition is a special case of no great
practical interest. Land's discussion implies that nobody has noticed
before that color perceived to belong to patch of light or an object de-
pends on factors other than radiant flux coming from it.
Long established that color perceived to belong to patch of light must
be based not only on color of patch but also on those surrounding it and
those previously viewed. Author thinks chromatic adaptation bears heavily
on Land's results, but possibly other factors are more important. Also
discusses object-color constancy. Lack of familiarity with Helmholtz and
Helson principles has led Land to conclude erroneously that the facts of
color mixture play no role in object-color perception. Memory color: when
a familiar object depicted in a scene, color perception of it tends to be
changed in direction of color previously perceived to belong to that object.
Land's hypothesis that we need chiefly to consider the information in
the long- and middle-wave records is similar to the old disproved hypothesis
of the constancy of object-color perceptions regardless of color and amount
of illumination.
Color-constancy hypothesis really states that it is hard to fool an
observer even though incomplete information is provided for the object-color
perception; Land's hypothesis really states that it is hard to fool an ob-
server even though no short-wave information is given him.
Land has discovered that astonishingly satisfactory color pictures can
be produced by a wide variety of choices of projecting lights by two primary-
color projection, and that object-color perceptions are substantially inde-
pendent of this choice.v He discovered that in evaluating the illuminant
color to be discounted, so as to arrive at a valid prediction of object-
color perception, only the scene in which the object is observed should be
assessed; other scenes within the visual field are irrelevant. "This exper-
iment gives the first premonition that multiple color universes can coexist
side by side, or one within another." This is true, and follows from
Helmholtz's view that an essential basis of object-color perception is dis-
counting of th6 illuminant color.
Has discovered that in a scene depicting objects shown by two-primary
color projection, objects will be perceived as having essentially no hue if
amounts Cl and C2 of primaries in all portions of the scene conform to the
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relation log C1 = a log C2 + b, regardless of values assigned to constants
a and b. That is, scene is perceived as chromatic but signals arriving
through optic nerve are so processed as toascribe chromatic character en-
tirely to the illuminant.
Two-primary color processes must fail to yield faithful color rendition
to an extent greater than the all too large departures from reality afflict-
ing current three-primary color processes.
Reports of object-color perceptions differ. How can we determine which
of a number of interpretations of an ambiguous visual field will be most
commonly perceived? The best answer that has been available heretofore is
that ascribed to a most gifted student of visual perception, Dr. Adelbert
Ames, "What the eye sees is the mind's best guess as to what is out front."
Perhaps Land's generalization (about conditions necessary for objects de-
picted by two-color projection to be perceived as having no hue) will prove
to be a reliable guide as to what the mind's best guess will be.
38. Hans Wallach, "Perception of Neutral Colors," Scientific American,
Vol. 208, No. 1, Jan. 1963, pp. 107-116.
Lightness and darkness are properties of surfaces (not of light).
Amount of light reflected by a neutral surface depends not only on its re-
flectance but also on intensity of illuminating light. Light message re-
ceived from a reflecting surface is therefore an ambiguous cue to its reflec-
tance or "actual" color. But perceived neutral colors are usually in good
agreement with the reflectance of the surface; for example, a dark gray object
tends to look dark gray in all sorts of light. Katz demonstrated "constancy
effect" with lighted and shaded gray samples. Effect however is incomplete.
One variable, the intensity of reflected light, depends on both in-
cident illumination and reflectance of surface. Experiment with dark gray
sample against light-colored wall. With room dark, sample looks luminous.
As room lightened, luminosity disappears and becomes white; constancy is
absent. Further increase in illumination changes to light gray. Light
reflected by dark sample is evaluated in terms of general illumination on
wall; light from projector is ignored. Against a surround of white card-
board, sample looks dark gray; constancy restored and changes in light in-
tensity hardly affect color of sample or surround. In neutral colors, com-
bination of dark gray surface with white surround is resistant to changes in
illumination. Surround of any other color fails to produce constancy.
Helson suggested that incoming light intensities are evaluated in terms of
"weighted average" of stimulation in different parts of retina. Perceived
neutral colors depend on ratio between light intensities reflected from
adjacent regions -- not on intensity of light as such. Ratio principle
operates best when ring and disk are presented against dark background, or
when ring fills whole visual field.
Luminosity sensation. Larger of two contrasting areas tends to look
luminous; lack of contact between two surfaces increases luminosity.
Special case of reduced contact: intensity gradient replacing sharp border
between areas of different intensities. When intensity difference becomes
greater than 4 to 1, area of higher intensity becomes luminous as well as
white; with very large difference it loses all whiteness (e.g., moon by day
and by night).
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These facts can be explained by considering that stimulation with light
gives rise to two perceptual processes: one, which causes luminousness, di-
rectly dependent on intensity of stimulation and state of adaptation of eye;
second, which produces the opaque colors, is an interaction -- area of re-
tina that receives higher intensity of stimulation induces sensation of
gray or black in neighboring region of lower intensity, with particular
color roughly dependent on ratio of intensities.
Experiments demonstrate that lightness of chromatic (as well as neutral)
colors depends on relation between intensities of stimulation of different
regions. Appearance of disk of chromatic light varies, for example, from
yellow to brown, depending on intensity of surrounding ring of white light.
Modes of a earance of chromatic colors. surface colors, opaque colors
of objects. Expanse colors (blue sky) in large homogeneous regions, lack
density and opaqueness of surface colors. Aperture colors observed when
seen through hole in screen at chromatic surface beyond it: surface appears
like transparent chromatic film stretched across hole. Raising illumination
on screen transforms Ttfilm" into a surface color, like piece of colored
paper attached toscreen.
39. Alphonse Chapanis, "Color Names for Color Space," American Scientist,
Vol. 53, No. 3, Sept. 1965, pp. 327-346.
In comparative judgments of color, normal eye could theoretically dis-
tinguish more than 7,000,000 colors (i.e. 200 in hue or "wavelength" circle
times 450 variations in lightness times 15 to 165 steps in saturation). In
absolute judgments, individuals can only name 12 to 13 colors without appre-
ciable error. Observers are internally consistent, that is, repeat their
own judgments accurately, but differences between individuals disconcertingly
large, for example, yellowish-green to one is bluish-green to another.
Literary and advertising English uses thousands of color names but
common English only about 12, with a few modifiers many of which turn out to
be synonymous to the average observer. (e.g. vivid, strong, pure and just
unmodified "red" mean the same).
Graph p. 341 gives average hue selections for the strong hues, against
Munsell hues (note not same.) When authors selected 19 basic color names
for experiment, tried to pick names which would fall in Munsell circle at
equal intervals. Results show that large region between most of the Munsell
greens and all the blue-greens that was not sampled at all by color names.
Another large empty space between greenish blue and blue and another between
violet and purplish pink. Eye can discriminate between these colors if it
wants to, but we have not found them sufficiently interesting to reward
them with distinctive names.
Violet and purple almost completely synonymous to observers, also
yellowish green and yellow-green.
Theoretical results: There are 45 different color names for which
selections should not overlap. But 18 percent of color chips were never
selected in experiment; theoretically 45 only covers about 82 percent of
Munsell color space. Total number of different color names probably 52 to
55. Note that results might have been different if experiment conducted in
British,. English, or French (learning important).
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40. Reports by Medical Research Laboratory, U. S. Naval Submarine Base,
New London, Conn.
, "Preliminary Report on Color Vision Testing," Color Vision
Report No. 1, Sept. 12, 1942, AD 622 180.
C. W. Shilling, "Report on Trial of Royal Canadian Navy Color Vision
Lantern in Comparison with other Tests of Color Vision," Color
Vision Report No. 2, 18 January 1943 (Reprinted May 1951)
AD 622 181.
D. Farnsworth and J. D. Reed, "A Survey of Methods Used in Administering
Pseudo-Isochromatic Test Plates for Color Vision," Color Vision
Report No. 3, 6 November 1943 (Reprinted January 1950) AD 622 183.
D. Farnsworth, J. D. Reed and C. W. Shilling, "The Effects of Certain
Illuminants on Scores Made on Pseudo-Isochromatic Tests," Color
Vision Report No. 4, 22 November 1943 (Reprinted December 1948)
AD 622 185.
D. Farnsworth and J. D. Reed, "The Effect of Changing the Illumination
on the Colors in Pseudo-Isochromatic Plates," Color Vision Report
No. 5, 3 January 1944, AD 622 220.
F. L. Dimmick, "The Psychological Dimensions of Color," Report No. 431,
1 June 1964, AD 612 551.
M. H. Siegel, "Discrimination of Color: IV, Sensitivity as a Function
of Spectral Wavelength," Report No. 436, 31 July 1964, AD 611 725.
41. Reports by U. S. Naval Submarine Medical Center, Submarine Base,
Groton, Conn.
Whitman Richards and Saul M. Luris, "Color Mixture Functions at Low
Luminance Levels," Report No. 439, 27 October 1964, AD 618 590.
M. M. Connors and M. H. Siegel, "Differential, Color Sensitivity in
the Purple Region," Report No. 445, January 1965, AD 618 592.
S. Weissman and J. S. Kinneg, "Relative Yellow-Blue Sensitivity as a
Function of Retinal Position and Luminance Level," Report No. 447,
26 February 1965, AD 618 594.
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B.8 ACUITY
42. Davson, op. cit.
Visual Acuity is defined as reciprocal of angle, in minutes, subtended
by the smallest detail which can be seen under given conditions. This is a
purely operational definition and there are in fact as many different "visual
acuities" as there are types of test object. A tendency to give visual
acuity an ontological status (that is, to treat it as if it had reality) has
sometimes led to confusion. There is no reason to expect that acuity values
will be the same or vary in the same manner for different test objects. I
Problem of acuity is different: (1) in the case of test objects with
one or several gaps which must be detected by eye, or a grating of equidistant
parallel bars, and (2) in case of simple detection of an object, such as a
black dot or line on illuminated field. In Case 2, it is sufficient for
object to produce detectable difference of stimulation by comparison with
surrounding field, whereas in Case 1, a detectable difference must be pro-
duced between retinal stimulation corresponding to gap and that due to other
parts of the object itself.
In case of grating consisting of parallel black bars, it is possible to
produce "deterioration" of image by using a grating in which bars half as
wide as before, but with the same number of bars per unit angle. Differences
of illumination in image then reduced to one-half previous value, while gen-
eral shape of smooth periodic variations of illumination across image remains
the same. Yet the eye resolves the grating as well. Conclusion: factor
which sets the limit to acuity in these experiments is not capacity for in-
tensity discrimination of rows of adjacent cones receiving blurred images of
black and bright bars, but anatomical separation between the cones. Maximum
acuity must be reached when all the single-cone units are active.
Limiting acuity value is about the same for blue, red, and white light.
At high intensities lights of all wavelengths probably stimulate all types
of central cones, so that sensitivity differences between cones may become
unimportant with regard to acuity.
In acuity experiments, subjective observations showed that more and
more central parts of retina used as luminance increased. Acuity values up
to about 1/8 obtained with peripheral regions of decreasing eccentricity;
between 1/8 and 1/1.4 using foveal regions some distance away from the cen-
ter; higher values using regions near or at the center. Thus it appears
that more peripheral retinal regions are more sensitive to light but less
accurate for acuity. In the periphery this is readily understandable if
there is increased spatial physiological summation as move away from central
fovea.
Vision of steadily exposed objects under natural conditions must be
dependent on eye movements. Physiological mechanism of acuity may then be
different from that involved in case of brief flashes. Slight eye movements
must be inefficient at scotopic levels because of indefiniteness of stimulus
itself.
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Subjective effects of contrast are probably due to inhibitory inter-
actions, but in many cases such effects seem to be useless or misleading
optical illusions. Subjective contrast as a rule is observed only when the
relevant differences in the external field are easily seen. There is no evi-
dence that subjective contrast, as such, helps in the detection of nearly
liminal differences -- but presence of inhibitory mechanisms underlying con-.
trast may, indirectly, do so.
Acuity of isolated cone mechanisms. Curves p. 190 suggest that "blue"
mechanism acuity reaches a plateau, the "green" mechanism taking over at
higher intensities because it is more accurate in discriminating detail.
Brindley (1954) experiments. Best visual acuity under ordinary condi-
tions is mediated by center of fovea. Here the "blue" mechanism is relatively
insensitive. One of possible explanations for this would be that there are
fewer "blue" cones in this region than near the edge of the fovea. If so,
central acuity would be determined largely by the other cone mechanisms.
Because of great width of spectral sensitivity curves of the various
cone mechanisms (see Ch. 14) high luminances of any spectral composition
should be capable of stimulating all these cones and would thus always lead
to the same acuity values. These are only speculative considerations, but
at any rate show that there is little reason to suppose that existence of
cones of different spectral sensitivities implies that the limiting acuity
value for high luminances under ordinary conditions must be smaller for
narrow spectral bands than for white light. At high intensities, mechanisms
other than blue may function as single-cone units, so that, when all suffi-
ciently stimulated, may be able to mediate an acuity corresponding to the
inter-center distance of the cones.
Acuity of rod monochromat. At scotopic luminances when most accurate
part of retina is used, relation between luminance and acuity similar to
normal, but acuity fails to increase at higher luminances as it does in the
normal, Part of the curve which attributed to cones or cones-rods is missing.
B.9 FLICKER
43. Davson, op. cit.
Flickering appearance of a light source which extinguished at regular
brief intervals disappears when number of extinctions per second becomes
large enough. Critical fusion frequency (number of complete cycles of light
and darkness per second) lowest frequency at which this happens. Luminance
of flickering light is main factor that influences c.f.f.: at high luminances
may exceed 100, in most lab experiments rarely more than 60. When c.f.f.
exceeded, apparent steady luminance of field bears simple relation to light
emitted during one cycle: ratio of time of exposure to total time. At lower
frequencies light no longer appears steady and peculiar subjective effects
often observed (see Le Grand). For instance, if wide colored field of high
luminance, flickering at 40-50 per second, presented in periphery while fix-
ation maintained, field looks white shaded with violet. When flicker suddenly
changed to steady illumination, color appears with high saturation. Critical
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fusion frequency may be regarded as measure of time-resolving power of the
visual system. It depends on luminance of field, area of field, region of
retina stimulated, light-dark ratio in each cycle, state of adaptation of
eye, and other physiological and psychological factors.
Retinal position. For eccentricity 0, area stimulated contains mainly
cones; results give simple curve which probably corresponds to cone function.
For eccentricity 50 curve shows marked division into two branches; low-inten-
sity branch is ascribed to rod function. At lowest illumination, flicker is
more easily detected by periphery than by fovea.
Wavelength. At higher illumination, results for all spectral bands fall
roughly on same curve. Low-intensity branch extends toward lower illumina-
tion as w.l. becomes shorter (p. 209). For violet (450 m?) and blue light
(490 m?) over certain range of low illumination, the c.f.f. is almost inde-
pendent of retinal illumination. Over this range the rod system is working
near its maximum efficiency with regard to detection of flicker. At highest
illumination, c.f.f. for cone branch also becomes approximately constant.
Binocular flicker. When both eyes stimulated together, c.f.f. is higher
for flickering fields which are in phase than for those out of phase, but
difference is not larger. When intermittent stimuli are out of phase, total
flux of light reaching visual system is constant. Any simple hypothesis of
summation between eyes, according to which flicker should never be seen with
out-of-phase binocular stimulation, is thus ruled out. Yet, as c.f.f. is not
sharply defined on frequency scale, possibility remains that binocular
effect may be explained on basis of probability summation. Peckham and Hart
(1960) conclude that binocular response to flicker involves some kind of
facilitation between two monocular responses, which takes place at a neural
level beyond the chiasma (intersection of optic nerves).
44. Vernon E. Carter, "Image and Cue Enhancement Through the Use of Moving
or Flickering Presentations, an Annotated Bibliography," Northrop
Nortronics NSS Report No. 2697, 15 August 1963.
45. H. E. Henkes and L. H. van der Tweel, eds, Flicker: Proceedings of
Symposium on Physiology and Clinical Electroretinography, Sept. 1963,
Hague, 1964
Book contains many detailed articles on psychophysics as well as physi-
ology of flicker. In article by C. R. Cavonius "Color Sensitive Responses
in the Human Flicker-ERG", pp. 109-110:
Changing adapting field wavelength causes selective effects in spectral
sensitivity of human ERG; these effects are in the expected direction, i.e.
to selectively depress responses to stimuli at or near wavelength of adapt-
ing field. But effects are so slight that of little value in quantifying
nature of fundamental color receptors.
Easier to account for results in terms of model which uses separate
system to mediate brightness, either by unique brightness receptor or by re-
cording of signals from color receptors. In either case the ERG response to
fast flicker would be primarily a measure of activity in brightness system,
which, since not concerned with hue, is unaffected by selective adaptation of
color systems.
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A final explanation for the lack of color explanation is based on one of
the most compelling arguments for separate brightness and color systems: fact
that color flicker and brightness flicker fuse at very different frequencies.
If two colors alternated and intensities properly adjusted, may be made to fuse
at rate under 20 flashes/sec. This suggests that color mehcnaisms may re-
spond poorly to fast flicker. Le Grand and Geblewicz 1937 found that colored
field presented extra-foveally and flickered at 40-50 flashes/sec. lost satur-
ation and turned white. If flickering field suddenly replaced by steady
field of same color, this now appeared more saturated than comparison field
which never flickered. They suggest that the color mechanism may be inhibited
by flicker. (Note: this last appears probable, but theories by Cavonius on
separateness of brightness and color mechanisms, on basis of different fre-
quencies of fusing, seem to be non seq.)
Article by P. L. Walraven and H. J. Leebeek, "Phase Shift of Alternating
Coloured Stimuli." Lange found that sometimes luminance flicker cannot com-
pletely be eliminated by adjustment of luminances of two alternating stimuli
of different wavelength. The residual flicker can be eliminated by shift of
phase of one stimulus with respect to the other. This is thought to be com-
pensation for a phase shift between the responses to these stimuli somewhere
in the retinocortical system.
B.10 FATIGUE
1
I
46. Davson, op. cit.
Experiments with large field and long exposures give steep frequency-
of-seeing curves and range of uncertain seeing of order of 1 to 2. Shares
of biological variations and quantum fluctuations cannot be determined with
certainty. But even if uncertainty range were entirely due to biological
variations, could not exceed 1 to 2. This suggests that, in the small brief
flash experiments also, biological variations may not have exceeded range
of 1 to 2, whereas observed range is of order of 1 to 10.
Biological variations become combined in complicated manner with quantum
fluctuations and with possible physiological complications; cannot be studied
in isolation. Non-independence of successive responses to flashes indicates
that biological variations do occur in some experiments; purely quantum fluc-
tuations would be random and lead to independence in successive trials.
When subject is tired or unwell, range of uncertain seeing may increase.
Some untrained subjects give very shallow frequency of seeing curves, which
become steeper with practice. This must be due to changes in extent of bio-
logical variations. In properly conducted experiments it has proved im-
possible to obtain variations smaller than the minimum predicted by the
quantum theory.
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47. Woodburn Heron, "Pathology of Boredom," Scientific American, Vol. 196,
No. 1, January 1957, pp. 52-56.
Research by Mackworth on radar operations on antisubmarine patrol to
find out why they sometimes failed to find U-boats. Worked in isolation
watching screen continuously. In similar lab situation subjects' effi-
ciency declined in half an hour.
Experiments in a rigidly monotonous environment, from which all patterned
or perceptual stimulation removed, to test effects on mental performance.
Oral tests performance impaired by isolation in monotonous environment, and
poorer than that of control group. Ability to think impaired. Experimental
situation induced hallucinations. Hallucinations have also been reported in
experiments where subjects exposed for long periods to blank visual fields of
flickering light. Hallucinations began with simple forms and progressed to
integrated scenes. Subjects had little control over content; auditory as
well as visual. When subjects emerged after several days of isolation, whole
room appeared to be in motion, surfaces appeared curved, and objects changed
size and shape. Slow brain waves (typical of sleep) appeared, and frequencies
in region of principal brain rhythm slowed down.
Normal functioning of brain depends on continuing arousal reaction
generated in the reticular formation, which in turn depends on constant
sensory bombardment. Sensory stimuli in addition to specific functions,
maintain arousal, but lose power to do so if they are restricted to repeated
stimulation in unchanging environment.
48. W. Heron, B. K. Doane and T. H. Scott, "Visual Disturbances After Pro-
longed Perceptual Isolation," Canadian Journal of Psychology,
Vol. 10, No. 1, March 1956, pp. 13-18.
Apparent movement of objects, distortion of shapes, intensification of
colors. Hallucinations continued when closed eyes or replaced goggles.
Effects observed after isolation are not due merely to forgetting or per-
ceptual habits. Exposing subject to monotonous sensory environment can
cause disorganization of brain function similar to, and in some respects as
great as, that caused by drugs (such as mescal and lysergic acid) or lesions.
49. W. H. Bexton, W. Heron and T. H. Scott, "Effects of Decreased Variation
in Sensory Environment, Canadian Journal of Psychology, Vol. 8,
No. 2, June 1954, pp. 70-76.
College students used as subjects in this experiment refused to remain
under conditions of "homogeneous input" even though paid $20 day.
50. Roland H. Moore and Wendell E. Bryan, "The Practical Application of
Research on Visual Factors in Stereoplotting," Photogrammetric
Engineering, Vol. 30, No. 6, Nov. 1964, pp. 991-999.
1959 study of eye fatigue in stereoplotting in Denver office of USGS.
Recommended higher level of ambient light: more comfortable and eliminated
visual shticks of abrupt changes in light levels. Optometrist serving as
consultant devised questionnaire to evaluate individual opinions of experi-
mental changes; designed loupe for scribing. Examined eyes, found assorted
defects. Recommended continuous optometric service. Recommended elimination
of traditional isolated room. Response of participants to questionnaire
varied when given three times (see graphs).
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B.11 INTERPRETATION OF COMPLEX IMAGES
11
51. R. H. Kause, "Interpretation of Complex Images: Literature Survey,"
Goodyear Aerospace Report GER 10830, Rev. A, 10 February 1965,
AD 614 703.
Selected references and abbreviated abstracts from this report of parti-
cular interest to photointerpretation are cited below along with additional
references within this general category.
52. F. Rhodes, "Predicting the Difficulty of Locating Targets from Judgements
of Image Characteristics," Aerospace Medical Research Lab Technical
Document Report No. AMRL-TDR-64-19, March 1964.
Search time to locate targets.
Overall target difficulty.
Factors involved: target size, picture sharpness and contrast, pic-
ture detail, logical restrictions on possible target location,
target shape and pattern, target location, target isolation, rater
bias.
Conclusions: "Raters were able to make highly reliable and seemingly
reliable judgements about complex perceptual characteristics of
aerial photographs. There was no difference in reliability or
validity between ratings made by PI's and those made by untrained
students."
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53. M. A. Whitcomb, ed., Visual Problem of the Armed Forces, Washington,
D.C., NAS-NRC, 1962.
Proceedings included:
1. Vision under reduced stimulus conditions.
2. Perceptual problems of space travel.
3. Pictorial display for reconnaissance interpretation.
4. Visual processes and problems of battlefield surveillance in
ground warfare
54. H. R. Blackwell, J. G. Ohmar and R. W. Brainard, "Experimental
Evaluation of Optical Enhancement of Literal Visual Display,"
ASD Tech. Report 61-568, October 1961.
"When the probability of detection (in a photo) was low or moderate
at gamma = 1, increases in gamma were accompanied by increases in the
probability of detection; when it was high at gamma = 1, detection proba-
bility either remained unchanged or decreased slightly with increased gamma.
"Of the spatial filtering masks studied, some always reduced the prob-
ability of target detection, whereas the most effective increased this prob-
ability at the lower values of detection probability.
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"....unless the probability of recognition is known beforehand, optical
enhancement should be done only at operator's discretion."
55. R. E. Reilly and W. H. Teichner, "Effects of Shape and Degree of
Structure of the Visual Field on Target Detection and Location,"
JOSA, Vol. 52, 1962, pp. 214-218.
Square fields generally superior to round ones.
56. J. N. Enoch, "Effect of the Size of a Complex Visual Display upon
Visual Search," JOSA, Vol. 48, 1958, p. 867.
Greatest attention paid to center of screen.
For displays smaller than 9 0 subtense, as displays decreased, durations
of fixation increased, interfixation distances decreased, concentrations of
attention in the central area increased, and efficiency decreased.
57. E. S. Zaman, S. Hecht, S. Schlair and C. D. Hendley, "Size, Shape and
Contrast in Detection of Targets by Daytime Vision," JOSA, Vol. 37,
1957, pp. 531-545.
"For small targets (< 100 sq. min.) square targets require less contrast
than rectangular ones for recognition. All measurements can be unified on
the supposition that the visually critical region of a target is a ribbon
just inside its perimeter and 1 min. wide. Evidently, contrast is not
judged over the area of a target, but across its boundary."
58. R. Sadacca, "New Techniques in Image-Interpretation Systems," Presented
at the Seventh Annual Army Human Factors Engineering Conference, 1960.
1. Degree of confidence a PI expresses in his identification.
Expanding the scale by which interpreters express confidence
in their judgements to a 5-point scale seems to achieve a more even distri-
bution of accuracy percentages.
2. Efficient viewing-time periods
The average accuracy of the interpreters falls off the longer they
examine the imagery.
3. Performance feedback to interpreters
Knowledge of how well they are doing may be effective in reducing
the number of errors made by P.I.'s especially if feedback is made in such a
way that they can see exactly what kind of errors they are making.
4. Repeated exposures to the same imagery
The accuracy (for a tactical exercise) for objects that P.I.'s
reported, both times they examined the imagery, was significantly higher than
for objects reported only incl. (53% vs. 34%)
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5. Teamwork Procedures
P.I.'s working in groups of 2 or 3 show a marked decrease in the
numbers of false responses and a lesser decrease in the number of correct
responses.
59. R. Sadacca, J. E. Ranes and A. I. Schwartz, "Human Factors Studies in
Image Interpretation: Vertical and Oblique Photos," USAPRO Technical
Research Note No. 120, Dec. 1961.
Tests on graduates of Image Interpretation Course, Ft. Holabird.
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Results indicate that having both vertical and oblique photos of a
target area does not necessarily make for improved interpreter performances.
60. R. Sadacca, A. Castelnovo and J. Ranes, "The Impact of Intelligence
Information Furnished Interpreters," HFRB Technical Research Note
No. 117, June 1961.
Army P.I.'s furnished additional intelligence information; a larger
proportion was consistently above the median in correct identification of
objects in the photographs; this group also reported more objects where
actually none appeared.
61. J. Zeidner, R. Sadacca and A. I. Schwartz, "The Value of Stereoscopic
Viewing," HFRB Technical Research Note No. 114, June 1961.
Number of objects reported tended to be higher under the nonstereo
viewing condition. Findings indicate: 0) need for stereo capability should
be demonstrated before new display equipment is developed for use of mili-
tary P.I.'s;(2) future studies should examine additional interpreter
functions and systematically take into account such photo factors as quality,
content, and format.
62. C. A. Baker and W. F. Grether, "Visual Presentation of Information,"
WADC Tech. Report WADC TR-54-160, Aug. 1954.
General human engineering recommendations for aiding in design of the
most satisfactory visual presentations of information.
1. Mechanical Indicators
2. Warming Devices
3. CRT's and Signal Coding
4. Printed Materials
5. Instrument Panel Layout
6. Lighting
7. Visual Detection and Identification
63. J. M. Enoch and J. A. Fry, "Visual Search of a Complex Display: A
Summary Report," The Ohio State University Mapping and Charting Research
Lab, MCRL T. P. No. 696-17-282, April 1958.
A series of eight experiments to identify major factors encountered in
search performance.
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64. G. A. Fry and C. A. Townsend, "The Effects of Controlling the Search
Pattern of a P.I.," RADC Tech. Report RADC TN-59-533, Sept. 1959.
Machine-generated search patterns (using a ring or outline square) that
give complete and uniform coverage are useful primarily when the targets are
difficult to find. Under good visibility free search is much preferred.
Under these conditions, peripheral vision is more effective, and tests show
that on the average, free search represents a faster way of finding a target.
65. G. A. Fry and J. M. Enoch, "Human Aspects of Photographic Interpretation
Fourth Technical Report," The Ohio State Mapping and Charting Research
Laboratory, MCRL 4th I.T.R., AD 232 142.
Markedly increased probability of detection in the center of a photo.
66. G. A. Fry, "Human Aspects of Photo Interpretation (Addendums to Final
Summary Report)";RADC Tech. Report 61-29B, May 1961 (Secret).
Studies effect of photo grain, blur, contrast, size and shape on photo
interpretation; image-enhancement techniques, TV grain; search patterns,
possible control and usefulness in assessment of P.I.'s task.
67. M. N. Crook, "Visual Factors Affecting Efficiency in the Task of Photo-
interpretation," Feb. 1960, ASTIA Document 232 175.
1. General illumination.
2. Illuminance for color transparencies.
3. Differential illumination in stereo viewing.
4. Binocular viewing of duplicate photos.
5. Visual fatigue.
68. S. L. Smith, "Color Coding and Visual Search," Journal of Experimental
Psychology, Vol. 64, 1962, pp. 434-440.
Series of colored targets against either white or black background.
When target color was known in advance, search times were considerably
shorter than when unknown. Where target color was unknown search times
were not significantly different than those for single-colored display.
69. D. E. MacDonald, "Criteria for Detection and Recognition of Photographic
Detail," BU ORL Tech. Note No. 72, Oct. 1950.
Worthwhile discussion of role of P.I. and need to raise his ability to
raise the overall quality of aerial reconnaissance.
70. Philco Advanced Technology Laboratory, "Semiautomatic Imagery Screening
Research Study and Experimental Investigation, Vol. I," July 1963,
ASTIA Document AD 410 261.
Discusses photoscreening problem and possible design solutions.
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71. R. J. Hall, J. W. Miller, D. Musselman, R. Earl, and M. H. Detambel,
"A Study of Visual Display Enhancement and Techniques of Color Filter-
ing," Electronic Systems Div. Tech. Document Report 63-635, Dec. 1963.
Viewing filtered photos proved superior to viewing the unfiltered ones.
Differences resulting from the two degrees of display control were small but
favored the condition of more complete observer control. Operators had choice
of one-at-a-time viewing or superimposing. Those with this freedom found in-
creased detectability.
72. C. L.Klingberg, C. L. Elworth and C. L. Kraft, "Identification of Oblique
Forms," Tech. Report No. RADC-TDR-64-144, Aug. 1964, AD 607 357.
Oblique photography (aerial recon.). Discusses form constancy - refers
to identity in perception of plane forms as they vary in orientation or pro-
jection transformation. Complete form constant, doesn't exist, so they are
preferred viewing angles for best discrimination or recognition performance.
This "best view" may be desired either because the salient features of an
object are more apparent or because the mental picture of the objects cor-
responds to the view.
Reduce search time by:
1. Being selective in the type of photography obtained.
2. Being selective by presenting the most promising imagery to the P.I.
first, instead of having him waste time in less useful material.
What a P.I. sees in a photo depends on his past experience, near and
remote. Probability of seeing (i.e. being cognizant of) a given target de-
pends in part on his expectancies. Higher probability of detection if told
to expect a target. Detecting probability affected by wishes - leads some-
times to false reports.
If experience has been with one view, detection probability may be much
lower than for a P.I. having fewer but more varied views of the target.
Quote by Hake:
"Thus perception itself, or the ability to 'see' a form demands prior
information about what forms generally are like in the world. And conversely,
memory for a particular form is stored not as an isolated description but in
terms of the categories of experience found useful in the past in interpreting
input information about forms. It is convenient to talk of these categories
as 'schemata' - maybe a preferred schemata (i.e. orientation of, e.g., draw-
ing a truck.)"
Boynton and Bush (1955) indicated that they were unable to obtain evi-
dence of detections without recognition, that is, a critical target response
when one was actually present in the array, but a response which was incor-
rect as to which of the six classes of critical target it belonged.
Detection - observer identified an object of interest but can't categor-
ize it further.
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Recognition - observer identifies object as belonging to a particular
class of objects or as having particular attributes. This can be broken
down into increasingly specific categories. Recognition implies prior ex-
perience since one cannot categorize a completely novel object.
Conclusions - Near vertical best for aircraft, high oblique best for
ships.
73. Harriet W. Foster, "Information Displays and Information Processing
Tasks," SDC SP-1811, Sept. 9, 1964.
Ordinarily one thinks of a visual search task as a search for a known
target. It should be clear, however, that the uncertainty concerning what
kind of target will appear can vary from complete certainty to extreme
uncertainty, such as a search for "something interesting," for example.
74. Robert W. Brainard and George N. Ornstein, "Image Quality Enhancement,"
North American Aviation, Inc., AMRL-TR-65-28, Behavioral Sciences Lab,
Wright-Patterson AFB, AD 616 895.
Enhancement of photos using flying spot scanner to obtain a video signal
and then adding its first and/or second derivative(s). Resolution, contrast
and acuitance measured. Results indicated differentiation enhances image
quality, greatest enhancement occurring with operations involving second-order
differentiation.
Edge-gradients play significant role in visual perception. Perceived
contrast is "formed over the boundary of an object" (Perrin, F. H. - "Methods
of Appraising Photographic Systems, Part I, - Historical Review": J. SMPTE,
69: 151-,56, 1960) that is, over the spatial-luminance transition connecting
adjacent areas.
If the edge-gradient is sufficiently shallow, the difference between
adjacent luminance areas in an image will not be detectable even though the
brightness differential, i.e. contrast between the two areas is well above
contrast. Also by properly shaping the edge-gradient, the apparent contrast
may be made to oppose that of this actual spatial-luminance distribution of
the image, and.in some cases to produce apparent contrast where none actually
exists.
With blurred images, having significantly reduced edge-gradients search
time increases the duration of the visual fixations increases and the dis-
tance between fixations decreases as the edge-gradients are diffused.
Rationale for enhancement technique.
Even with sharp edge-gradient between object luminance areas the dis-
tribution of illuminance at the retina will be spread or diffused due to
diffraction, spherical and chromatic errors, scattering of light. In spite
of this, the retinal image is often perceived as being sharp and distinct.
Perception of bipartite field - edge-gradient much sharper than retinal
image would indicate;- observed first by Mach, who suggested that the effect
was describable as a second derivative correction applied to the retinal
image. The equation proposed was
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r (x) = a log e(x + e ) d2 e 2
dx
1
where x is the axis along the retina surface
r is the perceived (or apparent) brightness
e is the retinal illuminance
a, P, and 'y are constants.
Mach also found first derivative of spatial-luminance distribution has
little or no effect on perception.
B.12 MISCELLANEOUS AND GENERAL
1
75. One of the most useful source references on the subject of vision is
the Annual Review of Psychology, published by Annual Reviews, Inc. of Palo
Alto, California. Each year a different author searches the literature and
presents an up-to-date review of activities in the field of vision. Of
particular value is the very extensive bibliography which is published at
the end of each review.
The bibliography of the Annual Reviews of Psychology is listed below.
Bartlett, N. R.: Vision, Vol. 1, 1950
Chapanis, A.: Vision, Vol. 2, 1951
Helson, H.: Vision, Vol. 3, 1952
Vernon, M. D.: Vision, Vol. 4, 1953
Riesen, A. H.: Vision, Vol. 5, 1954
Thomas, G. J.: Vision, Vol. 6, 1955
Mueller, C. G. & Berger, E.: Vision, Vol. 7, 1956
Pickford, R. W.: Vision, Vol. 8, 1957
Riggs, L. A.: Vision, Vol. 9, 1958
Gebhard, J. W.: Vision, Vol. 10, 1959
Hurvich, L. M. & Jameson, D.: Color Vision, Vol. 11, 1960
Mueller, C. G.: Visual Sensitivity, Vol. 12, 1961
Boynton, R. M.: Spatial Vision, Vol. 13, 1962
Armington, J. C. & Biersdorf, W. R.: Color Vision, Vol. 14, 1962
Onley, J.: Visual Sensitivity, Vol. 15, 1963
Westheimer, G.: Visual Acuity, Vol. 16, 1964
De Valois, R. L. & Abramov, I.: Color Vision, Vol. 17, 1965
76. "Human Factors Design Standards for the Fleet Ballistic Missile
Weapon System," Vol. I - Design of Systems, Vol. II - Design of Equip-
ment, May 1963, NAV WEPS OD 184 134
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77. Davson, op. cit.
Because of complex psychological factors which cannot be reproduced in
laboratory, visual performance in practice may be difficult to correlate with
lab tests. Correlations may exist,.but fail to be detected because of varia-
tions introduced by psychological factors.
78. G. Kepes, ed., Education of Vision, Vol. I, Vision and Value, George
Braziller, 1965.
In Volume I of this three volume series, psychologists lead off with
analyses of fundamental characteristics of seeing. Arnheim attempts to es-
tablish "visual thinking" as an operation valid in its own right, not an
instrument for other means of knowing. Holton, a physicist, discusses
vision as implement for understanding physical world.
79. A. C. Crombie, "Helmholtz," Scientific American, Vol. 198, No. 3,
March 1958, pp. 94-102.
Helmholtz was trained in medicine and was physicist, physiologist, and
philosopher. Gave law of conservation of energy its broadest and most
definitive formulation. Study of optics; invented ophthalmoscope; physics
of sound and theory of vowel tones; relations of optics to painting.
Theory of knowledge: "Sensations are, as regards their quality, only
signs of external objects, and in no sense images of any degree of resem-
blance." Only connection between sensation and object is that both appear
simultaneously. Sensations are "signs that we have learned to decipher...
a language given us with our organization by which external objects discourse
to us."
Nature of electrical and magnetic forces: Three rival theories of
electromagnetic forces existed. Helmholtz showed that all three were special
cases of a more general mathematical theory and devised tests to determine
which special theory to be adopted. Left with that of Faraday and Maxwell
that electric and magnetic forces are propagated through an all-pervading
ether. Mathematical interpretation of Maxwell's theory that light is another
form of electromagnetic wave stimulated Hertz to make experiments in electro-
magnetic radiation, which established theory of light and made radio communi-
cation possible.
80. Rene Dubos, "Humanistic Biology," American Scholar, Vol. 34, No. 2,
Spring 1965, pp. 179-198.
Success of comparative biology may have retarded growth of knowledge
about man himself. All living forms have many characteristics in common;
biologists and medical scientists tend to focus investigation on organisms
simpler and easier to manipulate in lab (e.g., horseshoe crab). This tendency
is based on widespread (but unproved) assumption that understanding of man
will eventually emerge from detailed knowledge of elementary structures and
functions that occur in all living things. A deplorable consequence of this
attitude is the common belief that the only fields of biology that deserve
to be called "fundamental" are those that deal with the simplest manifesta-
tions of life.
Failure to account at present for many cognitive and emotional aspects
of human life has origin in fact that words "mind" and "emotion" as commonly
1
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t
used cannot possibly refer to attributes located in fragments isolated from
the body or associated with special chemical reactions. Instead, they denote
activities of integrated organism responding as a whole to external or inter-
nal stimuli.
Higher the position of an animal on the phylogenetic ladder, the more un-
predictable its behavior with regard to environmental stimuli. Words "reac-
tion" and "response" symbolize wide interplay between man and environment.
At one extreme man appears as ordinary (though complex) physiochemical
machine, reacting with environmental forces according to the same laws that
govern inanimate matter. At other, man seems rarely a passive component in
the reacting system; characteristic aspect of behavior is that he responds
actively and creatively. Can shut out or modify some of stimuli or use their
effects to his selected ends.
All social stimuli -- crowding, isolation, challenge, have effects that
originate in evolutionary past (e.g. fright-flight) and tend to imitate kind
of response that was then favorable for survival, even when response no long-
er suitable to conditions of modern world.
Ancient biological traits explain such phenomena as mob psychology
aberrations, physical symptoms of anger, urge to control property and domin-
ate, aesthetic characteristics. Animal behavior also provides prototypes of
these (territoriality, dominance, aesthetic preferences).
These biological traits have been grossly neglected by biologists. This
neglect is the result of the historical accident.that scientific biology has
been identified from its beginning with concept that body is complex but
otherwise ordinary machine and that detailed analysis of its elementary
structures and energy mechanisms is the only valid approach to the under-
standing of the living organism. This attitude has discouraged the scienti-
fic study of biological problems that do not lend themselves to the reductionist
analytical methods now in vogue among experimental scientists.
Man's sense of discreteness is one of most cherished and pronounced
characteristics. Failure of theoretical biology to emphasize uniqueness of
individuals contributes to its lack of influence on the humanities.
Environmental influences contribute to shaping of personality by inter-
fering with acquisition of new experiences: aptitude to apprehend external
world becomes saturated as mind and senses are conditioned by repeated
experiences. Environmental influences also determine certain patterns of
response which can affect all manifestations of behavior, for example, end-
less variety of conditioned responses from dog salivation to Proustian
association with past.
Activity of neural processes in brain is continuous. Stimuli give form
to the activity rather than arouse inactive tissue. These findings, plus
knowledge that sensory deprivation causes transient disintegration of person-
ality, suggest that ways may be found to prevent or retard the setting of
personality.
Systematic effort should be made to describe and analyze pattern of
responses that man makes to all the stimuli that impinge on him. Such know-
ledge could be acquired if biologists devoted to study of living experience
as much skill and energy as have devoted to description of body machine.
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Animal kingdom provides experimental models for many of interesting problems
of human life. Biologists have been immensely successful in describing ele-
mentary structures and processes of body, but have neglected study of living
experience. Commonly stated that biology has become "too scientific" to con-
cern self with problems of humanness. In author's opinion difficulty is that
biology is not scientific enough. One of responsibilities of science is de-
velopment of objective methods for describing all aspects of reality.
81. Bernard Berelson and Gary A. Steiner, Human Behavior: On Inventory of
Scientific Findings, Harcourt, Brace, & World, 1964. (Reviewed by
Jules Henry in Scientific American, July 1964).
Publication of this book provides what is needed to consolidate a gen-
eral theory of intellectual failure in the behavioral sciences. Most signi-
ficant factors in failure: (1) inability to distinguish truism from
discovery; (2) insensitivity to platitude; (3) insensitivity to tautology;
(4) confusion of causal sequence;(5) misperception of variables; (6) delusion
of precision, or imagining instruments to be sharper than they are and throw-
ing away large but important minor percentages; (7) issue-avoidance; (8) draw-
ing of simple-minded parallels; (9) multiparaphrasis or repeated quotation
and misquotation; (10) failure to observe law of homologous extrapolation,
e.g. extrapolating laws of rat or pigeon learning to man, deriving proofs of
human behavior from experiments with lower animals; (11) lack of existential
concept of man. All above errors of judgment derive from fact that authors
avoid human existence.
Quotes from book 1 p. before end: "Indeed as one reviews this set of
findings, he may well be impressed by another omission perhaps more striking
still. As one lives life or observes it around him (or within himself) or
finds it in a work of art, he sees a richness that somehow has fallen through
the present screen of the behavioral sciences. This book, for example, has
rather little to say about central human concerns: nobility, moral courage,
ethical torments, the delicate relation of father and son or of the marriage
state, life's way of corrupting innocence, the rightness and wrongness of
acts, evil, happiness, love and hate, death, even sex."
Problem of glare studied by Stiles & Crawford (1937) and Crawford (1937)
who introduced concept of equivalent veiling luminance. This has proved its
usefulness in illuminating engineering, but this does not mean that it
necessarily reproduces all effects of glare, especially when these effects
are slight (Stiles, 1954).
Formula for calculating equivalent veiling luminance can be used to
estimate effect produced by a faint luminous fixation point on the threshold
measured using a test field distant from the fixation point. Shows that this
effect is probably negligible for a few degrees of angular separation between
field and fixation point (Pirenne & Denton 1951).
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INTRODUCTION
This paper describes a program of investigation into the areas of
vision, fatigue and illumination as these matters relate to the P.I.
task. The paper suggests area investigations through literature search,
through evaluation of current work and through interviews with the
active research workers to obtain comprehensive data in each field.
Once collected, that data will be "filtered" through the medium of
technically competent, experienced P.I.Ts and will then be synopsized
in handbook form with a supporting bibliography. Further, a continu-
ing lower level of effort is proposed beyond completion of the initial
study to maintain currency of information within the three indicated
fields.
THE PROBLEM
The effective accomplishment of a research, development and plann-
ing responsibility requires a high degree of currency in many technical
and scientific disciplines. Normally, only limited amount of the in-
vestigative work accomplished in any one discipline is germain to the
P.I. task. Thus, if the useful data are to be made available to the
development or planning officer, that person must research through
voluminous amounts of material to find the limited pertinent information.
The information is vital to successfully accomplish the R & D
The time requirements for obtaining the required information falls
beyond the capability of the R & D group who are normally faced with
significant numbers of other priority tasks.
SUGGESTED SOLUTION
proposes herewith, to undertake, in close liaison with the
customer's technical representative, a program designed to make readily
available all pertinent research results that stem from sound research
in the fields of:
1. Vision
2. Fatigue
3. Illumination
The program will concern itself solely with those aspects of the
investigative results which will be contributory to a group concerned
with the optimization of an image analysis system. This separation
of the useful data from the non-contributory shall be achieved by
having all materials obtained reviewed for pertinency by one or more
persons experienced in national level P.I.
Phase one of the program shall consist of an extensive search of
published works to thus gain useful data.
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Periodical publications to be reviewed include, but are not
limited to:
a.
American Scientist
b.
Applied Optics
c.
Vision Research
d.
Journal of the Optical Society of America
e.
Optica Acta
f.
Science
g.
Scientific American
h.
American
Journal of Psychology
i.
Canadian
Journal of Psychology
j.
Journal
of Applied Psychology
k.
Journal
of Engineering Psychology
1.
Journal
of Psychology
M.
Perceptual and Motor Skills
n.
Soviet Psychology
o.
Illuminating Engineering
p.
Industrial Lighting News
q.
Journal of SMPTE
r.
Lighting
s.
Optics and Spectroscopy
t.
British
Journal of Psychology
u.
Science
Progress
v.
Science
of Man
Books and similar works to be reviewed include, but are by no
means limited to:
a. Stevens, S. S. - HANDBOOK OF EXPERIMENTAL PSYCHOLOGY
Wiley & Sons, 1963.
b. Shurcliff, W. A., - POLARIZED LIGHT -.Harvard Univ., 1962.
c. Pollock et all - OPTICAL PROCESSING OF INFORMATION, Spartan
Books, 1962.
d. Wolf, E. - PROGRESS IN OPTICS, Volumns I, II, III, Wiley &
Sons, 1961-1962-1964.
e. Granit, R. - RECEPTORS AND SENSORY PERCEPTION - Yale Univ.
Press, 1955/62.
f. Luckiesh & Moss - THE SCIENCE OF SEEING - Van Nostrand, 1938.
g. Brindley, G. S., PHYSIOLOGY OF THE RETINA AND THE VISUAL
PATHWAY - Edward Arnold (London) 1960.
h. Henkes, H. E. et al, FLICKER, Junk (The Hague) 1963.
Also the extensive holdings of the Defense Documentation Center
will be reviewed for pertinent research and reporting.
The second project phase shall consist of personal or mail
contacts with those authors and industries found in Phase I, whose
past publication work will probably be of value in the preparation
of a P.I. R & D group.':sTTTabulation of Pertinent Research Results".
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 In addition to persons "found" in the publications search, additional
research workers can be interviewed on the suggestion of the earlier
contacts or at the behest of the sponsoring organization. Each such
personal contact would be cleared with the sponsor's representative
before implementation.
TAT
The third phase of the proposed work shall consist of a tabula-
tion of significant results into a handbook format for use by the
sponsor. In addition, a full bibliography of useful research is
proposed (and will be referenced as required in the handbook) to
permit the user to quickly establish the identity of an individual
research worker and the full range of his experimentation, if his
results are referenced or included within the "Handbook".
Additional work on a continuing basis is recommended in order
that the handbook and its companion bibliography shall remain current
and in order that equipment/system design and planning shall take full
advantage of knowledge gains in vision, illumination and fatigue as
they relate to P.I.
REPORTING
Spot reports shall be submitted in all cases where work of high
pertinency is uncovered and should such work recommend, by implication
or analysis, specific action by the R & D group, that action shall be
suggested within the report.
Should specific voids in research become apparent in the latter
phases of the project, the, sponsor's attention shall be called to
those lacks in order that they may be examined as subjects for sponsored
research.
The proposed Handbook and Bibliography shall serve as a Final
Project Report except that an additional project "History" shall be
submitted as a basis for evaluation of the depth and thoroughness of
the proposed investigation.,'
PERSONNEL
It is recommended that function as Project
maturity and judgment. He has been an active P.I. since 1952 and was
employed as a P.T. within CIA from 1956 to 1962.
Manager for the proposed effort. This recommendation reflects
It is further recommended that) Ifunction
as the principal research worker in tree areas o~ document search and
STAT
STAT
STAT
data compilation, xperience in preparing STAT
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the "Manua o Photographic Interpretation" prove es an eminent
qualification for her inclusion in the proposed effort. Personnel
resumes of both persons are included with this proposal.
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 - 4 -
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In addition to
STAT would be available for consultation
STAT . as needed. last assignment before joining
was Chief/Publications Division CIA/PIC.
STAT
was a Photo
Intelligence Officer with CIA from 1953 to 1961 and functioned as a
member of the development staff of that organization for two years.
expertise covers both the vision process and color techno-
logy. Resumes of these persons are also attached hereto.
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