Acquired Equivalence of Discriminative Stimuli Following Two Concurrent Discrimination Learning Tasks as a Function of Overtraining in Rats

Abstract

Three experiments examined whether or not the members of each stimulus class between the discriminative stimuli formed during overtraining became functionally equivalent. In Experiment 1, rats were trained on two discrimination tasks to criterion or overtrained. Then they were tested on two new discriminations, in which the negative stimuli for the original discriminations were exchanged. This manipulation had little disruptive influence. on rats’ subsequent choices following overtraining, but not after criterion training. The effect of overtraining on exchanging the negative stimuli of two discriminations was replicated in Experiment 2. Experiment 2 makes it clear that the members of each pair of stimuli begin to become functionally equivalent after the rats receive overtraining for 10 days, and become perfectly functionally equivalent after the rats receive overtraining for 20 days. In Experiment 3, half of the rats were concurrently trained on two discriminations to criterion or overtrained. The remaining rats were separately trained in one discrimination on odd days in the training phase and the other on even days to criterion or overtrained. Then all rats received testing, in which the negative stimuli between two discriminations were exchanged. There was no significant difference in test performance after overtraining between these two groups, which were very excellent. Results of Experiments 1, 2, and 3 indicate that, in rats, stimulus classes established during overtraining have two properties of stimulus equivalence relation: exchangeability and substitutability.