Center for Avian Cognition


Date of this Version



Published in Journal of Experimental Psychology 76:4 (1968), pp. 609-617.


Copyright © 1968 American Psychological Association.


Rats were trained in 2 SD-SΔ discrimination experiments in which the effects of an SD-postponement contingency during SΔ and temporal regularity of SΔ duration were assessed. Experiment I showed that discrimination is markedly facilitated by the presence of an SD-postponement contingency of either fixed or variable duration. Experiment II showed that variable-duration SΔ periods in a noncontingent schedule can also greatly enhance formation of an operant discrimination. These effects were attributed to differences in the probability of adventitious reinforcement of SΔ behavior by SD events.