Comparing the effects of differential versus non-differential stimuli in two temporally defined schedules with equal probabilities of water delivery

Abstract

Two experiments were conducted to evaluate the effects of using the same reinforcement probability in the t^D and t^A subcycles of a temporally defined schedule. In both experiments a 60 seconds temporal schedule was used, t^D and t^A being 30 seconds long. In both experiments, t^D and t^A were matched in their probability of reinforcement, which was varied in succesive phases from 1.0, 0.75, 0.5, 0.25, 0, and 1.0, with a final phase in which t^D was correlated with a probability of 1.0 and t^A was correlated with a probability of 0. Each of the first four experimental phases was followed by five consecutive probe sessions using the same probability value. Reinforcement was delivered independently of responding at the end of each subcycle during probes. In Experiment 1, t^D and t^A were correlated-with different stimuli, whereas in Experiment 2 no stimulus was presented. In both experiments response frequency and the percentage of lost reinforcers per session were almost identical in t^D and t^A. Responding was lower during the probe sessions. In the last phase, when t^D was 1.0 and t^A was 0 responding dramatically increased in t. In Experiment 1, variability of responding and the percentage of lost reinforcers were lower than in Experiment 2. The results are compared with previous findings using temporally defined schedules and with the performance obtained under multiple and mixed schedules of reinforcement.