Psychopharmacology Section, Division of Psychiatry, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
J Exp Anal Behav. 2011 Jan;95(1):57-74. doi: 10.1901/jeab.2011.95-57.
Twelve rats made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately after a response and a larger reinforcer (B) that was delivered after a delay which increased or decreased by 20% depending on the subject's choices in successive blocks of trials. In two phases of the experiment (100 sessions and 40 sessions), reinforcer sizes were selected which enabled theoretical parameters expressing the rate of delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays obtained in the two phases. Indifference delays, calculated from adjusting delays in the last 10 sessions of each phase, were shorter when the sizes of A and B were 14 and 25 µl of a 0.6 M sucrose solution than when they were 25 and 100 µl of the same solution. The ratio of the indifference delays was significantly smaller than that predicted on the basis of an assumed linear relation between reinforcer size and instantaneous reinforcer value, consistent with a previous proposal that this relation may be hyperbolic in form. Estimates of the rate of delay discounting based on the ratio of the two indifference delays (mean, 0.08 s(-1)) were similar to values obtained previously using different intertemporal choice protocols. Estimates of the size-sensitivity parameter (mean 113 µl) were similar to estimates recently derived from performance on progressive-ratio schedules. In both phases of the experiment, adjusting delays in successive blocks of trials were analyzed using the Fourier transform. The power spectrum obtained from individual rats had a dominant frequency that corresponded to a period of oscillation of the adjusting delay between 30 and 100 trial blocks (mean, 78). Power in the dominant frequency band was highest in the early sessions of the first phase and declined with extended training. It is suggested that this experimental protocol may have utility in neurobehavioral studies of intertemporal choice.
十二只老鼠在一个调整延迟时间表上进行了重复选择，其中较小的奖励（A）在反应后立即提供，较大的奖励（B）在延迟后提供，延迟时间增加或减少 20%，具体取决于受试者在连续试验块中的选择。在实验的两个阶段（100 个和 40 个）中，选择了奖励大小，使得可以根据在两个阶段中获得的无差异延迟的比率来估计表示延迟折扣率的理论参数和对奖励大小的敏感性。在每个阶段的最后 10 个试验中，从调整延迟中计算出的无差异延迟在 A 和 B 的大小分别为 14 和 25µl 时比大小分别为 25 和 100µl 时更短。同一溶液。无差异延迟的比率明显小于基于假设的奖励大小和即时奖励值之间的线性关系所预测的比率，这与先前的建议一致，即该关系可能呈双曲线形式。基于两个无差异延迟的比率（平均值为 0.08 s(-1))）对延迟折扣率的估计与使用不同的跨期选择协议获得的值相似。基于在渐进比率时间表上的表现得出的大小敏感性参数（平均值 113µl）与最近的估计值相似。在实验的两个阶段中，使用傅里叶变换分析了连续试验块中的调整延迟。从单个大鼠获得的功率谱具有一个主导频率，该频率对应于调整延迟在 30 到 100 个试验块之间的振荡周期（平均值为 78）。主导频带中的功率在第一阶段的早期阶段最高，并随着训练的延长而下降。建议该实验方案可能对跨期选择的神经行为研究具有实用价值。
