Washington University, Department of Psychology, Saint Louis, MO 63130, USA.
J Exp Anal Behav. 2010 Sep;94(2):113-23. doi: 10.1901/jeab.2010.94-113.
Pigeons' discounting of probabilistic and delayed food reinforcers was studied using adjusting-amount procedures. In the probability discounting conditions, pigeons chose between an adjusting number of food pellets contingent on a single key peck and a larger, fixed number of pellets contingent on completion of a variable-ratio schedule. In the delay discounting conditions, pigeons chose between an adjusting number of pellets delivered immediately and a larger, fixed number of pellets delivered after a delay. Probability discounting (i.e., subjective value as a function of the odds against reinforcement) was as well described by a hyperboloid function as delay discounting was (i.e., subjective value as a function of the time until reinforcement). As in humans, the exponents of the hyperboloid function when it was fitted to the probability discounting data were lower than the exponents of the hyperboloid function when it was fitted to the delay discounting data. The subjective values of probabilistic reinforcers were strongly correlated with predictions based on simply substituting the average delay to their receipt in each probabilistic reinforcement condition into the hyperboloid discounting function. However, the subjective values were systematically underestimated using this approach. Using the discounting function proposed by Mazur (1989), which takes into account the variability in the delay to the probabilistic reinforcers, the accuracy with which their subjective values could be predicted was increased. Taken together, the present findings are consistent with Rachlin's (Rachlin, 1990; Rachlin, Logue, Gibbon, & Frankel, 1986) hypothesis that choice involving repeated gambles may be interpreted in terms of the delays to the probabilistic reinforcers.
鸽子对概率和延迟食物强化物的折扣研究使用了调整数量的程序。在概率折扣条件下，鸽子在取决于单次按键啄击的调整数量的食物丸和取决于可变比率方案完成的较大固定数量的食物丸之间进行选择。在延迟折扣条件下，鸽子在立即提供的调整数量的食物丸和延迟后提供的较大固定数量的食物丸之间进行选择。概率折扣（即，作为强化可能性的函数的主观价值）和延迟折扣一样，都可以用双曲函数很好地描述（即，作为强化时间的函数的主观价值）。与人类一样，当将双曲函数拟合到概率折扣数据时，其指数低于将双曲函数拟合到延迟折扣数据时的指数。概率强化物的主观价值与根据在每个概率强化条件下简单地将其收到的平均延迟代入双曲折扣函数而得出的预测值强烈相关。但是，使用这种方法，主观价值被系统低估了。使用 Mazur（1989）提出的折扣函数，该函数考虑了概率强化物的延迟的可变性，可以提高对其主观价值进行预测的准确性。综上所述，本研究结果与 Rachlin（1990；Rachlin、Logue、Gibbon 和 Frankel，1986）的假设一致，即涉及重复赌博的选择可以根据概率强化物的延迟来解释。
