Behavioral contrast in rats when qualitatively different reinforcers are used

Behavioral contrast was studied during multiple schedules which provided qualitatively different reinforcers in the two components. Five rats responded on a baseline schedule in which both components delivered food reinforcers (food-food), and then on a contrast schedule in which one component delivered food and the other delivered water (food-water). Following this, baseline was recovered. Five other rats responded on a baseline schedule in which both components delivered water reinforcers (water-water), then on a food-water schedule, and then on the baseline, water- water, schedule. Contrast was not observed when relatively low rates of reinforcement were use but it was sometimes observed when high rates of reinforcement were used. The rate of responding for a constant water reinforcer decreased when food replaced water in the other component. The rate of responding for a constant food reinforcer did not change when a water reinforcer replaced food in the other component. These results are similar to those reported by Ettinger and McSweeney (1981) when pigeons served as subjects.