Contingency tracking during unsignaled delayed reinforcement: Effects of delay duration and d-amphetamine

In two experiments, the role of the response-reinforcer relation in maintaining low-rate responding under unsignaled delay conditions was investigated. In both experiments pecking by pigeons on one response key, denoted the relevant key, was reinforced under an unsignaled delay-of-reinforcement procedure (defined as tandem variable-interval (VI) differential-reinforcement-of-other behavior [DRO] schedule). Responding on a second key, denoted the irrelevant key, had no programmed consequences. Between sessions, the location of the relevant key varied (after one, two, or three sessions) pseudorandomly. In Experiment 1, the delay (DRO) duration was manipulated parametrically. Overall, proportional relevant-key response rates (relevant-key response rates / [relevant-key response rates + irrelevant key response rates]) increased across 3-session sequences in which the relevant key remained in the same location and decreased as the DRO duration was changed systematically (2, 5, and 10 s). In Experiment 2, acute administration of d-amphetamine increased proportional relevant-key response rates during 1-day sequences for only the DRO 5-s duration, and results over 3-day sequences, once a discrimination had already been established, were inconsistent. Results support that the response-reinforcer relation is the primary determinant of responding, and such discriminations are relatively resistant to disruption or potentiation by behaviorally active doses of d-amphetamine.