Demand in rats responding under duration-based schedules of reinforcement.

In two experiments, demand curves were generated by exposing rats to a sequence of fixed-duration schedules in which the response requirement doubled each experimental session. Holding down the response lever for the requisite amount of time resulted in the delivery of sweetened condensed milk. Response durations shorter than those required for reinforcer delivery did not result in any programmed consequences, nor were cumulative durations across multiple presses applied towards the duration requirements. The number of reinforcer deliveries decreased as a function of reinforcer requirements. Reinforcer delays alone also decreased consumption, but to a lesser extent than increasing duration requirements. Results are congruent with previous research demonstrating that parameters of reinforcement schedules may have similar effects on both continuous and discrete dimensions of operant behavior. Hursh and Silberberg's (2008) exponential demand equation provided a good fit for several of the data sets.