Relative time, choice delay and delay of reinforcement in conditional discrimination

Abstract

Some recent studies reported inconsistent results about the effects of delay of reinforcement and retention interval in different procedures varying the intereinforcer interval (e.g., Schaal, Schuh & Branch, 1992; Shahan & Lattal, 2005; Williams, 1998, 2003). The study was designed to evaluate the effects of delay of reinforcement and the retention interval in different conditions, with an intertrial interval constant or variable. Rats were trained on a conditional discrimination procedure. In Experiment 1 the intertrial interval (ITI) was increased for a group (ITI variable), while for another group the ITI duration was constant, concurrently the stimulus-choice interval (retention interval) was increased. The effects of retention interval were smaller with longer ITI´s (variable group). Experiment 2 was a reply of Exp. 1, except the delay of reinforcement was increased (0, 2, 4 and 8 s). The percentage of correct responses was constant in all delay values. The occurrence of relative time effects in Experiment 1, but not in Experiment 2, suggest that different types of delay intervals (retention interval and delay of reinforcement) depend upon different psychological processes. The results are discussed in terms of differences in procedures and the generality of relative time effect.