Timing during inhibitory conditioning.

Analyses of second-by-second conditioned responding into a food receptacle by hungry rats (Rattus norvegicus) found that inhibition varies across the duration of a conditioned stimulus (CS) in a manner consistent with initial training. Variations in the arrival time of the unconditioned stimulus (US) supported temporally specific suppression of responding (Experiment 1). Summation and retardation tests (Experiments 2 and 3, respectively) revealed that points of greatest inhibition coincided with US omission at the time normally specified by the excitor. Our data provide a clear demonstration of fine-grained changes in the time course of inhibitory conditioning for the first time.