PERCENTAGE REINFORCEMENT AND BEHAVIORAL-CONTRAST IN CHAIN SCHEDULES

Intermittent reinforcement [in pigeons] may lead to higher response rates than 100% reinforcement when it is delayed and when there are stimuli during the delay that are correlated with the type of delay (reinforced or nonreinforced). Two experiments were carried out to evaluate the hypothesis that this effect is due to the same variables that are hypothesized to control behavioral contrast. In the 1st experiment, 2 chain schedules were arranged so that any contrast effect should appear in the chain terminating with 100% reinforcement rather than in the chain with 50% reinforcement. In experiment 2, an intertrial interval was employed to increase the amount of contrast in all chains and possibly wipe out the intermittent reinforcement effect. Increasing the intertrial interval did lead to a contrast effect but did not eliminate the effect of intermittent reinforcement. Some other mechanism, possibly the value of conditioned reinforcement, is responsible for this effect.