Responding on a multiple variable-time variable-time schedule as a function of component duration

Abstract

Five pigeons pecked lighted keys for food reinforcers delivered by a multiple variable-time 3D-sec variable-time 2-min schedule. The duration of the components varied from 5 sec to 16 min. The rate of responding generated by the more favorable component schedule decreased as component duration increased to an intermediate value and then increased with additional increases in duration. The decrease confirmed a prediction of additive theories of behavioral contrast. The rate of responding generated by the less favorable component did not increase as component duration increased. This decrease may represent a floor effect or it may violate a prediction of one additive theory of contrast.Gamzu and Schwartz (1973) placed hungry pigeons on several multiple variable-time variable-time (mult VT VT) schedules of food presentations. That is, they present food freely after variable intervals of time regardless of what the subjects did. Different rates of food presentation occurred in the presence of different color lights which alternated on a standard response key. The pigeons pecked the key at a high rate when it was illuminated by the stimulus that signaled the higher rate of food presentation (the more favorable stimulus). They pecked at a lower rate during the stimulus that signaled the lower rate of food (the less favorable stimulus). And they pecked both stimuli at a lower rate when the stimuli signaled equal rates of food presentation.Several recent, additive, theories have related these responses to the behavioral contrast which occurs when pigeons respond on multiple variable-interval variable-interval (mult VI VI) schedules of reinforcement (e.g., Gamzu & Schwartz, 1973; Hearst & Jenkins, 1974;Rachlin, 1973). Mult VI VI schedules are similar to mult VT VT schedules, except that food is not given freely. The subjects must perform a particular response to obtain it. Positive behavioral contrast refers to an increase in the rate of responding in one component which occurs when the rate of reinforcement obtained from the other component decreases. Negative behavioral contrast refers to a decrease in the rate of responding which occurs when the other rate of reinforcement increases.The additive theories differ in detail, but they a11