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This agreement is surprisingly close and gives confidence in the reliability if not
the validity of these measures. Their agreement with tc values obtained by curve-
matching is not nearly as impressive, the mean of that measure being 2.59 seconds.
The possible cause of this discrepancy is described be'l'ow.
The Position of the Asymptotic Level and Its Effect upon Recovery Rate Measurement
All methods described, whether curve-matching, t/2, D, or H/tan A, depend
for their validity upon the accurate choice of the asymptotic level to which the exponen-
tial portion of the recovery limb is decaying. The only exceptions to this are cases
in which E f /EA' or d (lo,,; E)/dt are used to determine tc. In the other four measures,
the conductance or resistance level at point of response onset has been used as the
asymptote, but it is clear from inspection that in numerous cases such an assumption
is error.: nus. Uncertainty as to the level of the asymptote, and in fact a systematic
error in estimating it may explain the fact that recovprv rate is found to have a
correlation with response ampli cue.. This correlation though low is consistent for
different methods of measurement and is significant. Examples of the correlation
for measures on the same population of 65 responses are:
r
p
Amplitude vs. Electronic tc
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