Effects of reinforcer type on rats' sensitivity to variation in reinforcer amount and reinforcer delay

Twenty rats, divided into two groups, served as subjects in an experiment that examined choices between reinforcers that varied in amount or delay. One group received food reinforcers, and the other water reinforcers. No difference was found between the two groups in their values of sA (tendency of choice behavior to vary in accordance with variation in reinforcer amount). However, Group Food had significantly lower values of sD (tendency of choice behavior to vary in accordance with variation in reinforcer delay) than did Group Water, and Group Food's values of s As D (a measure related to self-control-choices of larger, more delayed over smaller, less delayed reinforcers) tended to be greater than for Group Water. Finally, over the session, sA and s As D showed no significant change, overall response rates decreased, and sD increased. Taken together, these results suggest that, independent of deprivation level, self-control for water is less than self-control for food.