Marking and bridging versus conditioned reinforcement

Abstract

Rats were trained on a series of reversals of a two-choice conditional discrimination. Choice responses were followed by different delays of reinforcement, which were either unsignaled or filled with either a brief or a long tone. In some conditions, the tone occurred following both correct and incorrect choices; in other conditions, the tone occurred only after correct choices. Presentation of the tone following only correct choices greatly facilitated the acquisition of the discrimination, and there was little effect of the tone’s duration. Presentation of the tone following all choices did not improve discrimination acquisition relative to the no-signal condition. The results demonstrate facilitatory effects of a signal during a delay-of-reinforcement interval that are caused by the conditioned-reinforcement properties of the signal and cannot he explained by the alternative mechanisms of marking or bridging.