Time, trials, and extinction.

Four experiments investigated the effect of number of trials and total duration of nonreinforced exposure to the conditioned stimulus (CS) on extinction of Pavlovian conditioning. Rats were first trained in a magazine approach paradigm with multiple CSs, each paired with the unconditioned stimulus (US) on a variable CS-US interval. During subsequent extinction, CSs would differ in the number and length of their extinction trials but would be matched for the total duration of exposure (e.g., 1 CS would have 20 trials per session with a mean length of 5 s; another CS would have 5 trials per session with a mean length of 20 s). In each case, extinction proceeded more quickly for the CS given more trials per session. Indeed, there was no difference in rate of extinction between CSs that were matched on number of trials but differed on the duration of each trial, indicating that duration of exposure has no effect on extinction. We discuss the implications of these findings for trial-based and time-based theories of conditioning. (PsycINFO Database Record