Mazur James E, Biondi Dawn R
Department, Southern Connecticut State University, New Haven, CT 06515, USA.
J Exp Anal Behav. 2009 Mar;91(2):197-211. doi: 10.1901/jeab.2009.91-197.
An adjusting-delay procedure was used to study the choices of pigeons and rats when both delay and amount of reinforcement were varied. In different conditions, the choice alternatives included one versus two reinforcers, one versus three reinforcers, and three versus two reinforcers. The delay to one alternative (the standard alternative) was kept constant in a condition, and the delay to the other (the adjusting alternative) was increased or decreased many times a session so as to estimate an indifference point--a delay at which the two alternatives were chosen about equally often. Indifference functions were constructed by plotting the adjusting delay as a function of the standard delay for each pair of reinforcer amounts. The experiments were designed to test the prediction of a hyperbolic decay equation that the slopes of the indifference functions should increase as the ratio of the two reinforcer amounts increased. Consistent with the hyperbolic equation, the slopes of the indifference functions depended on the ratios of the two reinforcer amounts for both pigeons and rats. These results were not compatible with an exponential decay equation, which predicts slopes of 1 regardless of the reinforcer amounts. Combined with other data, these findings provide further evidence that delay discounting is well described by a hyperbolic equation for both species, but not by an exponential equation. Quantitative differences in the y-intercepts of the indifference functions from the two species suggested that the rate at which reinforcer strength decreases with increasing delay may be four or five times slower for rats than for pigeons.
采用调整延迟程序来研究鸽子和大鼠在强化延迟和强化量都变化时的选择。在不同条件下，选择项包括一个强化物与两个强化物、一个强化物与三个强化物以及三个强化物与两个强化物。在一种条件下，对一个选择项（标准选择项）的延迟保持恒定，而对另一个选择项（调整选择项）的延迟在一个实验时段内多次增加或减少，以便估计一个无差异点——即两个选择项被选择的频率大致相等时的延迟。通过将调整延迟作为每对强化量的标准延迟的函数进行绘图，构建无差异函数。这些实验旨在检验双曲线衰减方程的预测，即随着两个强化量的比例增加，无差异函数的斜率应该增大。与双曲线方程一致，鸽子和大鼠的无差异函数斜率都取决于两个强化量的比例。这些结果与指数衰减方程不相符，指数衰减方程预测无论强化量如何，斜率都为1。结合其他数据，这些发现进一步证明，对于这两个物种来说，延迟折扣都可以用双曲线方程很好地描述，而不能用指数方程描述。两个物种无差异函数y轴截距的定量差异表明，随着延迟增加，强化物强度下降的速率对于大鼠来说可能比鸽子慢四到五倍。
