Effects of partial vs consistent reward in noncontingent pairings of stimuli with reward: A noncontingently produced positive contrast effect

Abstract

Rats received pairings of two stimuli with reward noncontingently in the Skinner box. During noncontingent pairings, the bar was immobilized. For Group CC 100% of the presentations of both stimuli were rewarded (S, *, S2 *), for Group PP 50% of the presentations of each stimulus were rewarded (S, ±, S2±)' and for Group PC one stimulus was followed by reward on 50% of its presentations, while the second stimulus was followed by reward on 100% of its presentations (S, ±, S2*). A fourth group received the stimuli and reward nonpaired. In a subsequent rewarded test phase, the response facilitating effects of the stimuli were evaluated. In the test phase all groups that received reward paired with S, and S2 performed better in the presence of S, and S2 than the group for which the stimuli were not paired with reward. For groups that received the stimuli paired with reward, a difference due to schedule of reward occurred when schedule of reward was varied within Ss (Group PC), but not when varied between Ss (Group PP vs Group CC). The specific form of this finding was that Group PC's performance in the presence of S2 *was more vigorous than its performance in the presence of S, ± and was more vigorous than the performance of Groups PP and CC to S2' Group PC's performance to S, ± did not differ from that of Groups PP and CC to S,.Recently interest has developed in the effects of pairing the offset of stimuli with reward noncontingently, i.e., regardless of the animal's behavior. Customarily, during the noncontingent phase the animal is prevented from making the test response, e.g., in a Skinner box the bar may be immobilized during the noncontingent phase. One question of concern has been whether presentation of a stimulus that has been paired noncontingently with reward on 100% of its presentations (S:J:) will affect the vigor of the test response when presented before the response. It has been shown that performance of a previously learned response (Hyde, Trapold, & Gross, 1969), as well as acquisition of a new response (Trapold & Winokur, 1967), is more vigorous if an S:J: is presented rather than a stimulus that has not been paired with reward.The present experiment compared the facilitative effects of a stimulus that has been paired noncontingently with reward on 50% of its presentations (S±) with the facilitative effects of a stimulus that has been paired with reward on 100% of its presentations (S:J:). It might be expected on a number of grounds that responding in the test phase would differ in the presence of an S± and an S:J:, although which stimulus will produce greater response facilitation is not clear. For example, within anticipatory response theory, which has often been applied to data from noncontingent pairing studies, it is possible to predict greater response 39is assumed that the anticipatory goal response, rg-Sg, is less strongly conditioned when a stimulus is partially rewarded rather than consistently rewarded, it would be predicted that an S± would produce less response facilitation than an S:J...