Intertrial interval as a contextual stimulus in discriminated operant learning.

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Abstract
Previous research on Pavlovian conditioning has shown that the duration of the intertrial interval (ITI) can function like a contextual stimulus, modulating responding to an upcoming conditioned stimulus. Here, four operant learning experiments with rats investigated whether ITIs can similarly modulate operant responding occasioned by a discriminative stimulus (SD). In Experiment 1, responding for one group was reinforced during a 10-s SD when it was preceded by a 4-min ITI but not when it was preceded by a 1-min ITI (4+/1- discrimination). A second group had the opposite discrimination, 1+/4-. As seen with Pavlovian conditioning, rats could acquire discriminative control with the 4+/1- but not with the 1+/4- discrimination. Additional experiments investigated whether control by a temporal context in the 4+/1- discrimination transfers across physical contexts (i.e., the context provided by the operant chamber). In Experiment 2, rats learned the 4+/1- discrimination in one context (Context A), and the discrimination failed to transfer to a different context (Context B). In Experiment 3, the 4+/1- discrimination also failed to transfer to Context B when experience with reinforcers was equated across contexts. Experiment 4 found evidence of transfer, however, when rats had learned a second, nontemporal discrimination, in Context B. Overall, the findings suggest that ITI duration can acquire conditional control of discriminated operants in a manner similar to Pavlovian conditioned responses. The ITI arguably sets the occasion for a stimulus that itself sets the occasion for responding. Moreover, the control created by time can transfer across physical contexts under some conditions. (PsycInfo Database Record (c) 2025 APA, all rights reserved).
Funding Information
  • National Institutes of Health (R01 DA033123)
  • Department of Psychological Science, University of Vermont

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