CHOICE BETWEEN DELAYED REINFORCERS - INTERACTION BETWEEN DELAY AND DEPRIVATION LEVEL

Choice between two reinforcers differing in magnitude and delay was in vestigated in rats maintained at 80% (n = 10) or 90% (n = 10) of their free-feeding body weights using discrete-trials adjusting-delay sched ules in which the two reinforcers (S[mall] and L[arge]) were associate d with different levers. In each phase of the experiment the delay to the smaller reinforcer (d(S)) was held constant, and the delay to the larger reinforcer (d(L)) was varied in accordance with the distributio n of choices in successive blocks of trials. The value of d(S) was var ied across the four phases of the experiment (2, 4, 8, and 2 sec). Whe n d(S) was 2 sec, the mean value of dL was higher in the rats maintain ed at 80% than in those maintained at 90% of their free-feeding body w eights. When d(S) was increased, the value of d(L) increased in both g roups; however the effect of deprivation level was abolished. The resu lts are consistent with a model of choice that posits hyperbolic relat ions between reinforcer value and reinforcer magnitude, and between re inforcer value and delay of reinforcement.