Probabilistic reinforcement of reversal and dimensional shifts

Abstract

Thirty subjects learned 120 two-dimensional, 2-valued concept-identification (CI) problems over 5 days. After each problem was learned, the solution was shifted by interchanging responses (reversal shift, RS) or by picking a new dimension (dimensional shift, DS). Two groups with complementary probabilities of the type of shift were run. The probabilities of an RS for one group on the 5 days were: 1, 0, .7, .7, .7. The shift was so introduced that the subject's first response indicated the type of shift expected. The subjects learned to predict the shift and showed a tendency to follow the probability of the shift but with a bias toward the RS prediction. Negative recency and alternation tendencies occurred, but seemed to adapt out. The subjects improved greatly in trials to solution for each CI problem. A generalization of the cue-selection model designed to handle initially correct concept selection did not adequately describe the statistic of the trial of the last error, but a restricted randomization procedure accounted for the major deviations. The error distributions were more accurately described. The parameter which measured the initial probability of selecting the correct concept on the first trial also indicated that subjects approached probability matching in their expectations of the type of shift.