Coefficients of variation in timing of the classically conditioned eyeblink in rabbits

The time course of the conditioned response (CR) in rabbit eyeblink conditioning is highly attuned to the interstimulus interval (IST) between the onsets of the conditioned stimulus and unconditioned stimulus (US). In the present study, we reexamined data from a large number of experiments in two separate laboratories to determine whether CR timing conformed to a constant ratio analogous to Weber's law. Specifically, the mean and standard deviations (SDs) in the timing of the CR's peak were used to calculate coefficients 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 0.12 (SD = 0.045). The results are discussed with respect to real-time models of classical conditioning and scalar expectancy theory.