The effects of sequences of large and small reward on inhibition in Pavlovian conditioning

Ana Paz Goncalves Martins, Purdue University

Abstract

Three experiments, employing appetitive conditioning in rats, examined the extent to which the inhibitory effects of the memory of large reward stored on one trial, give rise to reduced responding on the following trial. The sequential model predicts that the inhibitory effects of the memory of large reward should be seen from the outset of training, before the effects associated with other stimuli present during training have developed. In Experiment 1, two groups equated for reward magnitude earned either large or small reward on Trial 1 of pairs of trials, and one pellet on Trial 2, to determine what caused the lack of differential responding in two groups from one preliminary study, which had complete reward reduction (that is, a transition to zero pellets) from Trial 1 to Trial 2. However, surprisingly, it appears that large reward preceding a reduced reward was not inhibitory in Experiment 1. Experiment 2 was designed to directly compare the amplitude of the decrease in responding between groups with complete and incomplete (transition to one pellet) reward reduction. Consistent with the model, the group with complete reward reduction that retrieved the memory of large reward on Trial 2 showed less responding on the nonrewarded trial than the group that retrieved the memory of small reward. This reward magnitude effect was seen early in training, but by the end of acquisition the two groups did not differ and showed greater discrimination between Trials 1 and 2 compared to the other groups. Furthermore, the two groups in Experiment 2 with incomplete reward reduction did not show any sign of inhibition. Experiment 3 attempted to determine if greater discrimination between trials as a function of reward magnitude would be detected in a within-subjects procedure. Two groups in this study, one with complete reward reduction, the second with incomplete reward reduction, retrieved the memory of large reward and the memory of small reward on Trial 2 on different occasions. It was found that there was no better discrimination between trials of the couplets when large rather than small reward was retrieved. Moreover, the group with nonreward on Trial 2 showed greater inhibition on that trial than the group with incomplete reward reduction. Several hypotheses for these results are discussed, as well as their implications to the sequential model and other theories of Pavlovian conditioning.

Degree

Ph.D.

Advisors

Capaldi, Purdue University.

Subject Area

Experimental psychology

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