THE EFFECT OF REARING ENVIRONMENTS ON THE CONTRAFREELOADING PHENOMENON IN RATS¹

Abstract

Eight naive rats were reared in enriched or impoverished environments for 39 days after weaning and then lived in operant chambers, in which they could obtain food pellets freely or by lever pressing, for 25 or 30 days. The animals raised in an impoverished environment acquired the bar-press response quickly when placed in the operant chambers and maintained a preference for obtaining food via bar pressing. Animals raised in an enriched environment did not learn to lever press, as demonstrated by low levels of responding and the lack of bar pressing when free food was subsequently removed. It was concluded that restricting animals' postweaning environments facilitated learning in a choice situation, probably because of increased activity levels. The results are interpreted in relation to previous studies on rearing environments and on contrafreeloading.

Long-term contrafreeloading in rats during continuous sessions

“…Similar procedures have generally been employed in subsequent research, but it is not necessary for rats to have experience with response-contingent reinforcement or to be tested in discrete sessions with controlled deprivation in order for them to exhibit contrafreeloading. When naive rats were continuously housed in operant chambers with both free and response-contingent food available on CRF, leverpressing was acquired and maintained for 30 or 100 days (Coburn & Tarte, 1976;Kopp, Bourland, Tarte, & Vernon, 1976).When rats live continuously in experimental chambers with no food other than that produced by responding, their daily response rates increase as the value of a fixed ratio (FR) schedule is increased from CRF to FR240, so that roughly constant food intake is maintained (Collier, Hirsch, & Hamlin, 1972; see also Collier, Johnson, Hill, & Kaufman, 1986). This situation is referred to as a closed economy (see, e.g., Collier, 1983;Hursh, 1984).…”

“…Similar procedures have generally been employed in subsequent research, but it is not necessary for rats to have experience with response-contingent reinforcement or to be tested in discrete sessions with controlled deprivation in order for them to exhibit contrafreeloading. When naive rats were continuously housed in operant chambers with both free and response-contingent food available on CRF, leverpressing was acquired and maintained for 30 or 100 days (Coburn & Tarte, 1976;Kopp, Bourland, Tarte, & Vernon, 1976).…”

A note on the acquisition of responding for food in the presence of free food

“…In my estimation, the fact that this ever occurs is striking; that it takes only several days to develop is phenomenal. The finding by Coburn and Tarte (1976) that rats reared in enriched environments failed to acquire a barpress response appears attributable to the fact that .these animals only rarely strayed from the free food source (p. 92) and consequently made only infrequent contact with the programmed response-reinforcer contingency.…”

“…Yet Kopp et al (p. 52) reported that three of their four rats developed consistent barpressing within several days, a time period similar to that necessary for naive pigeons to learn a food-producing response in the presence of free food (Neuringer, 1969). Mcl.aughlin, Kleinman, and Vaughn (1973) reported that naive rats acquired a barpress response within 7 to 10 days, although responding was again maintained at a low rate, and Coburn and Tarte (1976) found that rats reared in impoverished environments began responding for food from the outset of their experiment.…”

“…However, I fear the authors have fallen victim to their own argument. They use the data from two studies (Coburn & Tarte, 1976;Kopp, Bourland, Tarte, & Vernon, 1976)which show a low rate of maintained responding to argue against the statement that animals acquire an operant response. Yet Kopp et al (p. 52) reported that three of their four rats developed consistent barpressing within several days, a time period similar to that necessary for naive pigeons to learn a food-producing response in the presence of free food (Neuringer, 1969).…”