Role of Discriminative Stimuli in Concurrent Performances: Duration of Changeover Delay

Abstract

Pigeons alternated between simultaneously available, variable-interval 90-sec. schedules using a Findley changeover response procedure. Responses on the left key resulted in reinforcers according to the variable-interval schedules, while responses on the right key altered the reinforcement contingencies on the left key and initiated a changeover delay. Concurrent schedules were in effect when a changeover response alternated both the reinforcement schedule and discriminative stimulus on the left key. When the changeover response alternated only the reinforcement schedule, but not the discriminative stimulus on the left key, a parallel schedule was in effect. The lengths of the changeover delays were manipulated for both the concurrent and parallel schedules. For concurrent and parallel conditions, the birds were nondifferential between the components in terms of the relative proportion of responses emitted, time spent, and reinforcers received. When changeover delay was varied, changeover response rate was inversely related to the changeover duration. However, for a given changeover duration, changeover rate was consistently higher in concurrent than in parallel conditions. For both concurrent and parallel conditions, left-key response rate during the changeover delay was consistently greater than during post-changeover periods. A change in the discriminative stimulus (concurrent conditions) facilitates, but is not necessary for, the maintenance of changeover responding. These data suggest that the elevated rate on the left key during changeover delay is not affected greatly by variation in the discriminative stimuli, though the role of Pavlovian conditioning cannot be completely ruled out.