Three experiments examined multiple-schedule interactions in a free-operant paradigm for rats. In Exps. 1 and 2 three rats each and in Exp. 3 five rats were given extended multiple variable-interval baseline training before being shifted to multiple variable-interval extinction. Visual discriminative stimuli and regular extinction, which allowed nonreinforced responding, were used in Exps. 1 and 2, but auditory discriminative stimuli and retraction of the lever to prevent responding during extinction were used in Exp. 3. Positive behavioral contrast was observed in only one out of six rats in Exps. 1 and 2, while negative induction was observed in the other five subjects. However, contrast was observed at some point in training for all five subjects in Exp. 3. The differential multiple-schedule interactions were attributed to the introduction of an additional stimulus-reinforcer dependency with regard to the presence vs absence of the lever in Exp. 3. Results support an autoshaping or additivity account of behavioral contrast.
Stimulus control in multiple variable-ratio schedules of reinforcement
