Factors affecting schedule-induced wood-chewing in rats: Percentage and rate of reinforcement, and operant requirement

Abstract

In Experiment I, rats were allowed to acquire either schedule-induced drinking or scheduleinduced wood-chewing behavior under a fixed-interval (FI) 60-sec schedule of food reinforcement, following which food was omitted from 20% and then 50% of interreinforcement intervals. Omission of food severely disrupted induced drinking but had relatively little effect on induced wood-chewing. Experiment 2 investigated wood-chewing as a function of reinforcement rate, using a range of FI schedules from 5 to 180 sec in duration. Both the amount of chewing per session and the relative time spent chewing were bitonica1ly related to reinforcement rate. In Experiment 3, schedule-induced chewing that had been acquired under a response-dependent schedule was found to persist under a response-independent schedule. Induced wood-chewing resembles other induced behaviors in important respects, but quantitative differences are also apparent.Falk (1961) showed that when rats were allowed to earn food pellets intermittently, in the presence of a water source, they developed the habit of drinking a small amount of water within each interpellet interval. Because it dramatically enhances the rat's water intake, this type of drinking has become known as "schedule-induced polydipsia," or SIP. Two decades of research have revealed SIP to be an extraordinarily reliable effect, by behavioral standards, and have produced a wealth of experimental results and of conflicting theoretical accounts (see reviews by Falk, 1971, and Staddon, 1977. Nevertheless, no satisfactory explanation of the rat's enhanced drinking under intermittent schedules of food availability has yet emerged.We have chosen to address the problem of SIP obliquely, by asking whether the phenomenon of schedule induction extends to activities other than drinking, to reinforcers other than food, and to species other than the rat. In this way, we hope to determine the extent to which SIP depends on special characteristics of the relationship between eating and drinking in the rat, as opposed to reflecting the operation of more general principles. We have recently confirmed that wood-chewing can occur as a schedule-induced behavior in rats when food is intermittently available, and have shown that induced wood-chewing (like SIP) is inversely related to level of food deprivation (Roper & Crossland, 1982). This finding supports the idea that schedule indueWe thank the SRC for financial support. Reprints may be obtained from: T. J. Roper, School of Biology, University of Sussex, Brighton BNI 900, England. 35 tion is a general phenomenon (for a critical review of other relevant evidence, see Roper, 1981). On the other hand, schedule-induced wood-chewing has so far proved relatively variable in its rate and probability of acquisition, and it differs from SIP in the precise temporal location of the behavior within the interfood interval (Roper & Crossland, 1981). Thus, induced activities other than drinking may not resemble SIP in all respects.In this paper, we pursue the analogy between...

Schedule-induced polydipsia: Interactions with wheel running

“…From the present analy-sis of the overall and temporal interaction of licking and running, it is clear that induced behavior does not necessarily have priority over noninduced behavior (see also Rileyet al, 1981;Roper, 1978;Segal, 1969). These data support the growing evidence that induced and noninduced behaviors may have no distinguishing characteristics other than induction (see Killeen, 1975;Roper & Crossland, 1982;Roper, Edwards, & Crossland, 1983;Wetherington, 1982).…”

Schedule-induced behavior in rats: Pellets versus powder

“…The decline in volume drunk by the pellet rats in the omitted-food condition compared with that drunk in the scheduled condition is commensurate with the decreased amount of food received in the former condition, suggesting that the pelletfed rats were drinking very little in the no-food intervals. This result agrees with observations on time spent licking the water spout in an omitted-food condition by rats receiving pellets (Roper et al, 1983). The interval data on spout licking from the present study will be presented in a later section.…”

“…In the omitted-food condition, no food was delivered on selected intervals of the schedule of reinforcement. The water licking of rats showing pellet polydipsia is similar in no-food intervals of omitted-food conditions to that in no-food conditions (Roper, 1981;Roper, Edwards, & Crossland, 1983). If rats receiving powder truly are not polydipsic, then their drinking under schedule should be the same as their drinking in the massed-food condition and in the no-food intervals of the omitted-food condition.…”

“…In addition, their drinking in the food and no-food intervals of the omitted-food condition should be the same. By contrast, the pellet rats should switch back and forth between polydipsic and nonpolydipsic behavior depending on whether or not they receive food in the interval (Roper et al, 1983).…”

The Temporal Organization of Behavior on Periodic Food Schedules

“…The temporal distributions of food-related behavior (head-in-feeder) quickly stabilized in Phase 2, when no access was allowed to the running wheel, oak chewing block, or the drinking tube. Roper, Edwards, and Crossland (1983) proposed that schedule-induced chewing may develop only if rats have ample exposure to the periodic food schedule before access to the oak block is allowed. The purpose of Phase 2 was simply to allow this exposure in order to encourage as many activities as possible to become induced.…”