The time course of the conditioned response (CR) in rabbit eyeblink conditi
oning is highly attuned to the interstimulus interval (IST) between the ons
ets of the conditioned stimulus and unconditioned stimulus (US). In the pre
sent study, we reexamined data from a large number of experiments in two se
parate laboratories to determine whether CR timing conformed to a constant
ratio analogous to Weber's law. Specifically, the mean and standard deviati
ons (SDs) in the timing of the CR's peak were used to calculate coefficient
s of variation (CV) for ISIs ranging from 200 to 1,300 msec. Both the mean
and standard deviations increased as the ISI was increased, but their ratio
(the CV) appeared to remain constant. The average of the estimates was 0.1
2 (SD = 0.045). The results are discussed with respect to real-time models
of classical conditioning and scalar expectancy theory.