| Abstract: | Choice between two reinforcers differing in magnitude and delay was investigated in rats maintained at 80% ( n = 10) or 90% ( n = 10) of their free-feeding body weights using discrete-trials adjusting-delay schedules in which the two reinforcers (S[mall] and L[arge]) were associated with different levers. In each phase of the experiment the delay to the smaller reinforcer ( dS ) was held constant, and the delay to the larger reinforcer ( dL ) was varied in accordance with the distribution of choices in successive blocks of trials. The value of dS was varied across the four phases of the experiment (2, 4, 8, and 2 sec). When dS was 2 sec, the mean value of dL was higher in the rats maintained at 80% than in those maintained at 90% of their free-feeding body weights. When dS was increased, the value of dL increased in both groups; however the effect of deprivation level was abolished. The results are consistent with a model of choice that posits hyperbolic relations between reinforcer value and reinforcer magnitude, and between reinforcer value and delay of reinforcement. |
