Do random time schedules induce polydipsia in the rat?

The present experiments investigated the role of signals for pellet delivery in the development of polydipsia on random time schedules. In Experiment 1, when an explicit signal or auditory stimulation from pellet dispenser operation was available to the rats, polydipsia developed in all ofthe animals. In Experiment 2, animals receiving signaled pellet deliveries developed polydipsia more quickly than those receiving unsignaled pellet deliveries. Furthermore, behavioral observations suggested that animals showing polydipsia in the unsignaled group may have been able to detect the operation of the pellet dispenser despite our attempt to mask such cues. In Experiment 3, the information value of pellet-dispenser cues was degraded by the operation of an empty pellet dispenser during the interpellet interval. Under these conditions, almost all animals did not develop polydipsia and the data suggest that for the few that did, pellet-dispenser cues were probably not responsible. Thus, the present findings suggest two conclusions: (1) In studies reporting polydipsia on random schedules, the animals may have been inadvertently provided with cues for pellet availability, and (2) although Pavlovian conditioning may be an important modulator of adjunctive behavior, other factors must also be considered.