The stimulus-response overshadowing phenomenon with VI versus FI schedules of reinforcement

Abstract

Previous research has shown that response rates on a variable interval (VI) schedule of reinforcement decrease if a brief response-produced signal is given prior to reward. One explanation is that the signal overshadows the response because it is a better predictor of reinforcement. The S-R overshadowing effect does not occur with variable ratio (VR) schedules, however. Tarpy, Lea, and Midgley (1983) explained this fact by suggesting that the signal functions to enhance the salience of the temporal interval offset on the VI schedule (a characteristic not possessed by VR schedules), which then overshadows the response. In this experiment, the salience of the temporal interval was enhanced in another way: signaled or unsignaled reward was provided to rats responding on either a VI or fixed interval (FI) reward schedule. As predicted, rates were lowest for animals receiving signaled reinforcement on an FI schedule and highest for those receiving unsignaled reinforcement on a VI schedule.