The Effect of Food-Pellet Reinforcement on Rats' Rates of Lever Pressing for 1% Sucrose Reinforcers across Several “Contrast” Procedures

Abstract

Recent research has indicated that food-pellet reinforcement, when upcoming in the second half of a session, increases rats' rates of lever pressing for low-concentration liquid-sucrose reinforcement in the first half (i.e., induction). The present study determined the effect of food-pellet reinforcement on responding for 1% sucrose across different “contrast” procedures. Experiment 1 employed a successivecontrast procedure and found that food-pellet reinforcement produced negative contrast (i.e., decreased responding). Experiment 2 employed one type of simultaneous-contrast procedure and found that food-pellet reinforcement produced neither contrast nor induction. Experiment 3 employed a procedure similar to those used in studies of behavioral contrast and found that food pellets produced an induction effect for responding for 1% sucrose. Because the above procedures differ in whether they employ between- or within-subject designs, Experiment 4 used both to determine the effect of delivering food-pellet reinforcement in one half of the session on response rates for 1% sucrose in the other half. It increased sucrose-reinforced response rates similarly in both designs. The present results make an empirical contribution to our knowledge of contrast/induction effects. They also outline the challenge for theories trying to account for results across different procedures.