On two effects of signaling the consequences for remembering

Abstract

Five pigeons were trained to perform a delayed matching-to-sample task in which red- and green-colored keys were presented as sample and choice stimuli, and the duration of a delay interval varied across trials. Experiment 1 investigated the effects on delayed-matching accuracy of signaling different durations of food access for the two correct responses (the differential-outcomes effect), and of signaling nondifferential but larger durations for both responses (the signaled-magnitudes effect). In Condition 1, a vertical bar on either sample signaled different rewards (or different outcomes, DOs) for correct red and correct green responses (0.5 and 3.5 sec, respectively), and a horizontal bar signaled equal durations of food access (or same outcomes, SOs) for these responses (1.5 sec). In Condition 2, the horizontal bar signaled equally large rewards for the two correct responses (3.5 sec), and the vertical bar signaled equally small rewards (0.5 sec). Delayed-matching accuracies were higher on DO trials than on SO trials, and they were higher on large-reward trials than on small-reward trials. However, analyses of discriminability estimates as a function of delay-interval duration revealed differences between the forgetting functions reflecting these two effects. Signaling DOs increased the initial level of the function and reduced its slope relative to signaling SOs, whereas signaling larger rewards increased the initial level of the function but did not affect its slope relative to signaling smaller rewards. Experiment 2 investigated whether the difference between the initial levels of DO and SO functions in Condition 1 resulted from overall longer food access on the former trials. However, varying the food-access times on SO trials across three conditions (0.5, 3.5, and 1.5 sec) failed to produce systematic effects consistent with this hypothesis. The results are discussed with respect to the mechanisms that could be responsible for the two effects.