Blocking the Acquisition of Stimulus Control in Operant Discrimination Learning

Abstract

<p> At least five different uses of the term "attention" can be detected in the literature on animal discrimination learning. One of these predicts "blocking": decreased learning about one of two covarying cues, resulting from prior training to discriminate on the basis of the other cue. In Experiment 1, four groups of 6 pigeons received different sorts of training in Phase 1; in Phase 2 all groups received go/no-go discrimination training in which positive trials (tone; pale red key) and negative trials (noise, pale green key) differed on both an auditory and a visual dimension. A group that received Phase 1 training to discriminate on the basis of the visual cue alone showed less stimulus control by tone-noise on a test given after all training than did a control group that received no Phase 1 training. It is concluded that acquisition of control by the auditory cue in Phase 2 was blocked by prior training to discriminate on the basis of the visual cue. Results for the two remaining groups and a detailed analysis of the test data rule out certain alternative explanations of the reduced auditory control, including the possibilities that it resulted from (a) the occurrence of any Phase 1 training, (b) partial reinforcement received during Phase 1 discrimination training, (c) training with an auditory value present but not predicting reinforcement during Phase 1, or (d) an interaction on the test for stimulus control. </p> <p> Three subsidiary experiments involving a total of 20 pigeons show that blocking the acquisition of visual control by prior training on an auditory discrimination may also occur, but do not conclusively demonstrate it. In a concluding discussion it is argued that, although the results of the first experiment are evidence for "blocking" as defined here, the results do not require a two-stage model of learning for their explanation. </p>