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 …

… As described above, prior to the current study, rats responded under a multiple fixed-duration
schedule under which long-duration reinforcement criteria (eg 20 s) would be followed by
shorter-duration criteria (eg 2 s). Although the discriminative stimuli associated with each
component were not present during the current study, a learning history in which persisting
through longer duration requirements would be followed by contact with shorter duration …
Our findings are consistent with those reported by Bauman (1991), who attempted to isolate the …