Instrumental Acquisition and Performance on Fixed-Interval Reinforcement as a Function of Incentive Contrast

Abstract

Four groups of rats were alternately magazine trained and bar-press trained on successive days. Two incentive-contrast groups both received 64% sucrose on magazine-training days; one group was shifted to 32% and the other to 8% sucrose reinforcement on barpress days. One control group received 32% sucrose on both types of days and a second received 8% sucrose on both. All reinforcements were on a 1-min. fixed-interval schedule. Both of the shift groups barpressed at a higher rate than their respective controls during early acquisition trials, but at a lower rate during later trials, on which asymptotic performance was approached. Interpretation of this two-phase result was suggested in terms of an increasing discrimination in the experimental Ss between magazine and barpress incentives.