Zentall Thomas R, Peng Daniel N, Rasul Laiba
Department of Psychology, University of Kentucky, Lexington, KY, 40506-0044, USA.
Learn Behav. 2024 Dec 20. doi: 10.3758/s13420-024-00660-1.
A decrease in the rate of reinforcement associated with one component of a multiple schedule is typically associated with a decrease in responding in that component as well as with an increase in responding in the unchanged component. This increase in responding, referred to as positive contrast, is thought to result from an increase in the subjective value associated with the unchanged component. Williams Animal Learning & Behavior, 19, 337-344, (1991) challenged this hypothesis in an experiment with pigeons in which Stimulus A, associated with a variable interval schedule, was always followed by Stimulus X, associated with extinction, while Stimulus B, associated with the same variable interval schedule, was always followed by Stimulus Y, also associated with a variable interval schedule. Although Williams found that most of the pigeons pecked more at Stimulus A than at Stimulus B (behavioral contrast), when the pigeons were given a choice between Stimulus A and B, they showed a preference for Stimulus B. In the present experiment (a slight modification from Williams's), we confirmed this finding. Although our pigeons pecked more at Stimulus A than at Stimulus B, they generally preferred Stimulus B, the stimulus that was not followed by extinction. This result suggests that positive contrast may not result from an increase in the subjective value of the unchanged component. Instead, it suggests that this version of positive contrast may result at least in part from the pigeons' attempt to get all of the reinforcers possible in the presence of Stimulus A before the extinction schedule begins.
与多重强化程序的一个成分相关的强化率降低，通常会伴随着该成分中反应的减少，以及未改变成分中反应的增加。这种反应增加，被称为正对比，被认为是由与未改变成分相关的主观价值增加所致。《威廉姆斯动物学习与行为》，第19卷，第337 - 344页，（1991年）在一项针对鸽子的实验中对这一假设提出了质疑。在该实验中，与可变间隔强化程序相关的刺激A之后总是跟着与消退相关的刺激X，而与相同可变间隔强化程序相关的刺激B之后总是跟着同样与可变间隔强化程序相关的刺激Y。尽管威廉姆斯发现大多数鸽子对刺激A的啄击比刺激B更多（行为对比），但当给鸽子在刺激A和刺激B之间进行选择时，它们表现出对刺激B的偏好。在本实验中（对威廉姆斯实验的轻微修改），我们证实了这一发现。尽管我们的鸽子对刺激A的啄击比刺激B更多，但它们总体上更喜欢刺激B，即后面不跟着消退的刺激。这一结果表明，正对比可能不是由未改变成分的主观价值增加导致的。相反，它表明这种版本的正对比可能至少部分是由于鸽子试图在消退程序开始之前，在刺激A出现时尽可能多地获得所有强化物。
