On the Constancy of the Rate of Responding under Variable-Interval Schedules

Variable-interval (VI) schedules are commonly regarded as maintaining a constant rate of responding. However, the pattern of responding in time sustained by a VI depends on the distribution of intervals with which it is constructed. In fact, it is thought that the type of VIs that sustain constant rate of responding are the constant-probability VIs. Yet, there is limited support in the literature for this view. Moreover, classical methods used to construct constant-probability VIs, based on approximations of the exponential distribution, only support a roughly constant rate of reinforcement in time. In a recent study, the Uniform-Exponential (UE) VI was introduced as a solution to achieve constant rate of reinforcement. Although results with the UE VI show only minor deviations from constant rate of responding, limitations in the preliminary study prevent determining a possible consistent pattern, calling for more research.