Academic journal article The Psychological Record

Punishment of Schedule-Induced Drinking by Lick-Dependent Delays in Food Presented at Different Frequencies

Academic journal article The Psychological Record

Punishment of Schedule-Induced Drinking by Lick-Dependent Delays in Food Presented at Different Frequencies

Article excerpt

Three food-deprived rats (80% of their free-feeding weights) developed schedule-induced drinking after being exposed to a multiple fixed-time schedule (FT 60-s FT 18-s) of food-pellet presentation. A 3-s signaled delay was then initiated by each lick, and the rate of licking was reduced to a much greater extent in the FT 18-s component in two rats. With these rats, a 9-s lick-dependent signaled delay then occurred in the FT 60-s component only, and a reduction was observed in licks per minute similar to that observed previously with the 3-s delay in the richer component. With the third rat the delays which were effective in reducing licking were 6 and 18 s in the FT 18-s and FT 60-s components, respectively. Measures of the percentage of interfood intervals with at least one lick produced less pronounced effects. These results suggest that the ratio between delay length and interfood interval length is critical for lick-dependent delays to be effective in punishing schedule-induced drinking.

Falk (1961) found that food-deprived rats exposed to a variable-interval schedule (VI 1-min) of food reinforcement drank excessive amounts of water concurrently with their performance of the operant task. This behavior is unusual because the rats were not deprived of water and no contingency was arranged between their drinking and the delivery of food. Falk (1971) suggested that this schedule-induced polydipsia was the prototype of a behavioral class named "adjunctive behavior," different from operant behavior. The amount of schedule-induced behavior is related to the parameters that define the food reinforcer, such as its magnitude or quality, the rate at which food is presented, or the animal's level of food deprivation (see reviews by Pellon, 1992; Reid & Staddon, 1990; Wetherington, 1982).

There is now considerable evidence showing that the rate of schedule induced drinking is sensitive to environmental consequences programmed in relation to the rats' licking, in a way similar to rats' lever pressing reinforced by food. For example, Bond, Blackman, and Scruton (1973) reported that schedule-induced drinking was reduced by a punishment procedure in which licking produced electric shocks. Pellon and Blackman (1987) showed that schedule-induced drinking can be reliably suppressed by lick-contingent delays in food presentation (see also Flory & Lickfett, 1974; Lamas & Pellon, 1995a). Reberg (1980) observed that schedule-induced drinking was increased when licks produced extra food and decreased when extra food was dependent on not licking. These functional similarities between adjunctive and operant patterns of behavior are important considerations for an adequate explanation of schedule-induced behavior.

The studies by Pellon and Blackman (1987) were the first to demonstrate convincingly a negative punishment effect on schedule-induced drinking. Well-established drinking induced by a fixed-time (FT) 1-min schedule of food pellet presentation (in which no operant response is required for food to be delivered) was punished by 10-s signaled and unsignaled lick-dependent delays in the delivery of food. The suppression of schedule-induced drinking was more marked and better modulated by signaled delays.

The literature on the effects of lick-dependent delays as punishers of schedule-induced drinking remains contradictory, however. Earlier reports suggested a relative insensitivity of schedule-induced drinking to being reduced or eliminated by delays in food presentation. Falk (1964) reported that drinking induced by a VI 1-min schedule of food reinforcement was not eliminated or even reduced by the imposition of a contingency that ensured a delay in food delivery of at least 15 s from the last lick. Hawkins, Schrot, Githens, and Everett (1972) reported that drinking induced by a FT 1-min schedule of food delivery was not reduced even by lick-dependent delays as long as 4 or 5 min. These studies arranged quite particular contingencies between licks and food delivery so that delays in food presentation were not initiated by all licks. …

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