Document Type



Experiment 1 has examined the effect of overtraining on shift learning in a simultaneous matching- (or nonmatching-) to-sample discrimination. Experiment 2 has examined how much overtraining is required for rats to form the concept of matching in a matchingto- sample discrimination. In Experiment 1, rats were overtrained on a simultaneous matching-to-sample discrimination or nonmatching-to-sample discrimination in a discrete threestimulus- presentation T-type jumping stand and were transferred to either a nonshifted (nonshift) or a shifted task (shift). Group Nonshift learned their subsequent shift task more rapidly than Group Shift, regardless of whether rats were tested on the matching-to-sample task or the nonmatching-to-sample one (symmetry of transfer effect). Experiment 2 shows that the apparent asymmetry of transfer effect is observed at reaching criterion (OT-O), whereas the symmetry of transfer effect is observed after 5 days, 10 days, 15 days, and 20 days of overtraining. These results indicate that overtraining is an obvious operational precondition for symmetry of transfer effect in matching- (or nonmatching-) to-sample discrimination in rats.