A MODEL EXPLAINING HOW ANIMALS PRODUCE VARIABLE-INTERVAL RATES (IRT, INTERRESPONSE TIME, MOLECULAR RATE, REINFORCEMENT SCHEDULES)

Responding and reinforcement on variable-interval schedules correspond when reinforcements are recorded as the relative frequency of interresponse time class, and responses are recorded as the relative dwell time for each interresponse time class. Casey (1980) predicts that this reinforcement distribution controls subsequent responding, a view opposed to Reynolds and McLeod's (1970) that it cannot. The basis of this disagreement is examined analytically. The reinforcement distribution is found to be based on the dwell-time distribution so that differential reinforcement occurs unless the two distributions are identical. When a variable-interval schedule reinforces exponentially distributed responding, an increase in rate is differentially reinforced. This tendency is an increasing function of reinforcement density. Examination of the relationships implied by these findings shows that animals produce variable-interval rates by apportioning time to molecular rates (reciprocals of the interresponse times) equal to the relative reinforcements those rates have received.