Temporal location of unsignaled food deliveries: effects on conditioned withdrawal (inhibition) in pigeon signtracking.

Standard models of Pavlovian conditioning neglect local effects of unsignaled unconditioned stimuli (USs) on learning and performance. Using the approach-withdrawal behavior of pigeons toward keylights as conditioned stimuli (CSs), the authors varied the specific times (5-110 s) that USs occurred before or after a CS. Withdrawal from a CS generally increased as the time between a US before and/or after the CS was lengthened. Combinations of 2 distant USs produced more withdrawal from the CS than either US alone, whereas combinations of a distant and a nearby US yielded behavior intermediate between that for either US alone. Postacquisition retardation tests supported similar conclusions. Based on the temporal isolation of CSs and USs, a tentative model was offered to summarize these data. The results and the model suggest that a more molecular, possibly perceptual approach to Pavlovian excitation and inhibition is needed.