THE ROLE OF TYPE OF RESPONSE IN THE APPEARANCE OF NEGATIVE CONTRAST OR POSITIVE INDUCTION IN RATS

Abstract

Rats may decrease (negative contrast) or increase (positive induction) their rate of responding for 1% sucrose reinforcement when 32% sucrose reinforcement is upcoming under different conditions. Previous research suggests that which effect occurs may depend on what motor response (i.e., licking vs. press a lever) isrequired to obtain the sucrose. The present study investigated this idea by having subjects make different responses in different halves of the session. Subjects either licked or pressed a lever for 1% sucrose reinforcement in the first half of the session. They then made the alternative response for 1% or 32% sucrose reinforcement, in different conditions, in the second half. In Experiment 1, both licking and lever pressing were operant responses. In Experiment 2, licking was strictly a consummatory response. Results showed that upcoming 32% sucrose tended to decrease responding for 1% sucrose in the first half of the session regardless of the response required in either half. Positive induction was never observed. The present results question whether type of motor response is a key factor in whether contrast or induction is observed. Instead, they suggest that the location that thesubstances are delivered and consumed is critical. Ultimately, understanding when one effect or the other will occur will enhance our understanding of eating-related behavior.Key words: negative contrast, positive induction, reinforcement, lever press, rat.