A reevaluation of the CS− hypothesis for schedule-induced polydipsia under intermittent schedules of pellet delivery

Abstract

Lashley and Rosellini (1980) have recently suggested that schedule-induced polydipsia (SIP) is determined by the occurrence of absolute periods within schedules of periodic food delivery which are associated with a low probability of food delivery, that is, CS-periods. To asseS8 this hypothesis, SIP was examined in the present experiments under three schedules-fixed time, variable time, and random time (RT)-which differed in probability of occurrence and/or duration (Experiment 1), and under a range of RT schedules in which the CS-period was systematically varied by changing the interpellet interval (Experiment 2). In both experiments, the level and temporal distribution of SIP did not seem to be related to the absolute period associated with the absence of food. Instead, SIP was more systematically related to the average length of the interpellet interval and, therefore, to the average period associated with no food. It was suggested that drinking under intermittent schedules of pellet delivery, that is, SIP, is determined by an average CS-period and not by an absolute period associated with the unavailability of food.

Do random time schedules induce polydipsia in the rat?

“…These findings, although in agreement with those of Allen and Weidinger (1980) and Shurtleff et al (1983), fail to replicate those of Lashley and Rosellini (1980), who found that an unsignaled RT 120-sec schedule did not produce polydipsia in the majority of their animals. This failure to replicate our earlier findings was particularly puzzling.…”

“…Concerning the disagreement between the studies which report polydipsia on random schedules (Allen & Weidinger, 1980;Shurtleff et al, 1983) and those which do not (Lashley & Rosellini, 1980;Millenson et al, 1977), the current findings emphasize that the observance of SIP may be largely dependent upon the presence of stimuli that are predictive of food availability. That is, in the studies that report polydipsia on random schedules, the animals may have inadvertently detected cues that were positively correlated with pellet delivery.…”

“…First, in those studies the pellet dispensers were mounted on the operant chambers and would therefore produce both auditory and vibrotactile cues. Second, at least in the Shurtleff et al (1983) study, the typical postpellet pattern of consumption was observed in animals on the RT schedule.…”

“…This reported difficulty of random schedules to induce polydipsia has not, however, been the universal result. Allen and Weidinger (1980) and Shurtleff, Delamater, and Riley (1983) have reported the development and maintenance of polydipsia on RT schedules that appears not to differ from that observed on fixed time (FT) or variable time (VT) schedules. An intermediate pattern of results has been reported by Keehn and Burton (1978), who did observe the development of drinking on an RI 6O-sec schedule, although this drinking was lower than that observed on a FI 6O-sec schedule.…”

Can surprising nonreward and adjunctive behavior influence each other?

“…Similarly, adjunctive drinking is reduced when food delivery is scheduled according to a random-interval schedule, yielding food at a constant probability in time (Millenson, Allen, & Pinker, 1977; but see Plonsky, Driscoll, Warren, & Rosellini, 1984). Interestingly, inserting a minimum postreinforcement interval during which food was not available increase drinking in a random-interval schedule (Shurtleff, Delamater, & Riley, 1983). Third, adjunctive behavior reduces corticosterone activation triggered by intermittent reinforcement: Providing access to water or nonnutritious substances that can be chewed reduced corticosterone levels during sessions of intermittent reinforcement (Dantzer, Gonyou, Curtis, & Kelley, 1987;Levine, Weinberg, & Brett, 1979;Osborne, Sivakumaran, & Black, 1979).…”