Behavioral contrast with changes in duration and rate of reinforcement

Behavioral contrast can be defined as an inverse relation between rate of responding in one component of a multiple schedule and conditions of reinforcement in the other components. The present study was an attempt to produce contrast with changes in duration of reinforcement. Pigeons pecked a key for mixed grain delivered by a multiple variable-interval variable-interval schedule. In Experiment 1, the reinforcer duration in the second component was decreased or increased, for different subjects, by a factor of two, four, and six from that delivered during baseline. These changes usually produced contrast. In Experiment 2, rate, duration, or rate and duration of reinforcement varied in the second component. Contrast was usually observed when only one variable was manipulated. When both variables were manipulated in the same condition, but in opposite directions, responding in the constant component usually changed inversely with the change in rate of reinforcement, not the change in reinforcer duration. The results demonstrate that changes in duration of reinforcement can produce contrast. They also increase the empirical base for which a successful theoretical account of contrast must encompass and the generality of contrast, which increases its potential practical implications.