Memories of reward events and expectancies of reward events may work in tandem

Abstract

A common assumption is that expectancies of reward events in instrumental tasks are established on the basis of Pavlovian conditioning. According to the tandem hypothesis, tested in the four runway investigations reported here employing rats, memories of reward events may serve as the conditioned stimuli eliciting expectancies. In Experiments 1–3, rats were trained under a schedule of partial reward (P), which did not produce increased resistance to extinction, and subsequently shifted to consistent reward (C). According to the tandem hypothesis, the shift to the C schedule should result in increased resistance to extinction if, as hypothesized, under the P schedule the memory of reward, SR, came to elicit the expectancy of nonreward,EN. This hypothesis was confirmed under a variety of conditions. It was shown that increased resistance to extinction could not be attributed to the P schedule alone, to the rats receiving two schedules, P and C, to stimuli other than SR eliciting EN, or to the rats forgetting reward-produced memories when expecting nonreward (Experiment 4). It was shown that the tandem hypothesis could explain the divergent findings obtained in prior studies employing a shift from P to C as well as in the present study.