Spontaneous response tendencies in noncontingent trials of a matching-to-position task in rats: Consequences for learning the matching and nonmatching task contingencies

Abstract

Previous studies have indicated that rats show differences in their acquisition of two closely related delayed response tasks in two-lever operant chambers: delayed matching to position and delayed nonmatching to position. In order to analyze these differences, separate groups of rats were exposed to alternative sets of noncontingent pretraining, during which their responses did not influence the reward outcome, prior to training on the matching contingency in Experiment 1 or the nonmatching contingency in Experiment 2. The alternative pretraining conditions included: fixed or random presentation of the sample lever, different levels of reinforcement of responses to the sample lever (0% or 50%), and different levels of reinforcement of responses to the choice lever (50% or 100%). When the sample lever was always on the same side, all rats adopted progressively strong side biases in responding to the choice levers, some to the same side as that of the sample lever and others to the opposite side, with approximately equal frequency. When the sample lever was presented randomly and not reinforced, rats again initially adopted strong side biases, the strength of which declined modestly with repeated training. Only when both the side of the sample lever and the probability of reinforcement of the sample response was 50% did the rats adopt a spontaneous tendency to match the sample and choice responses. This resulted in enhanced learning of the matching-to-position contingency and retarded acquisition of the nonmatching contingency. The results indicate that both spontaneous response tendencies and previous experience can influence rats’ acquisition of conditional discrimination tasks widely used in the study of short-term memory processes. © 1995, Psychonomic Society, Inc.. All rights reserved.