Discriminating between reward-produced memories: Effects of differences in reward magnitude

Abstract

The greater the dissimilarity between exteroceptive stimuli, the easier it is to discriminate between them. To determine whether a similar relationship holds for memories produced by reward events, rats in three runway investigations received trials in pairs, the number of food pellets (0.045 g) occurring on Trial 1 indicating whether reward or nonreward would occur on Trial 2. In each investigation, discriminative responding on Trial 2 was better the larger the difference in reward magnitude on Trial 1. This finding was obtained under a wide variety of conditions: for example, when the larger of two reward magnitudes on Trial 1 signaled nonreward on Trial 2 (Experiment 1, 10 vs. 2 pellets); when the smaller of two reward magnitudes on Trial 1 signaled nonreward on Trial 2 (Experiment 2, 10 vs. 2 pellets); and when the same magnitude of reward on Trial 1 signaled nonreward on Trial 2 (Experiment 3, either 5 pellets or 0 pellets). The findings obtained here indicate that the greater the dissimilarity between reward magnitudes, the greater the dissimilarity between the memories they produced and, thus, the easier it is to discriminate between them. It is suggested that the present results may provide a basis for understanding findings obtained in other instrumental learning investigations in which reward magnitude is varied.