Huskinson Sally L, Woolverton William L, Green Leonard, Myerson Joel, Freeman Kevin B
Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, University of Mississippi Medical Center.
Department of Psychology, Washington University.
Exp Clin Psychopharmacol. 2015 Jun;23(3):184-93. doi: 10.1037/pha0000015. Epub 2015 May 4.
Research on delay discounting has focused largely on nondrug reinforcers in an isomorphic context in which choice is between alternatives that involve the same type of reinforcer. Less often, delay discounting has been studied with drug reinforcers in a more ecologically valid allomorphic context where choice is between alternatives involving different types of reinforcers. The present experiment is the first to examine discounting of drug and nondrug reinforcers in both isomorphic and allomorphic situations using a theoretical model (i.e., the hyperbolic discounting function) that allows for comparisons of discounting rates between reinforcer types and amounts. The goal of the current experiment was to examine discounting of a delayed, nondrug reinforcer (food) by male rhesus monkeys when the immediate alternative was either food (isomorphic situation) or cocaine (allomorphic situation). In addition, we sought to determine whether there was a magnitude effect with delayed food in the allomorphic situation. Choice of immediate food and immediate cocaine increased with amount and dose, respectively. Choice functions for immediate food and cocaine generally shifted leftward as delay increased. Compared to isomorphic situations in which food was the immediate alternative, delayed food was discounted more steeply in allomorphic situations where cocaine was the immediate alternative. Notably, discounting was not affected by the magnitude of the delayed reinforcer. These data indicate that how steeply a delayed nondrug reinforcer is discounted may depend more on the qualitative characteristics of the immediate reinforcer and less on the magnitude of the delayed one.
延迟折扣的研究主要集中在同构情境下的非药物强化物上，在这种情境中，选择是在涉及相同类型强化物的替代方案之间进行。较少情况下，延迟折扣是在更符合生态效度的异质情境下，用药物强化物进行研究的，在这种情境中，选择是在涉及不同类型强化物的替代方案之间进行。本实验首次使用一种理论模型（即双曲线折扣函数），在同构和异质情境下检验药物和非药物强化物的折扣情况，该模型允许比较不同强化物类型和数量之间的折扣率。当前实验的目的是，当即时替代物为食物（同构情境）或可卡因（异质情境）时，检验雄性恒河猴对延迟的非药物强化物（食物）的折扣情况。此外，我们试图确定在异质情境下延迟食物是否存在量值效应。即时食物和即时可卡因的选择分别随数量和剂量的增加而增加。即时食物和可卡因的选择函数通常随着延迟时间的增加而向左移动。与以食物为即时替代物的同构情境相比，在以可卡因作为即时替代物的异质情境中，延迟食物的折扣率更高。值得注意的是，折扣不受延迟强化物数量的影响。这些数据表明，延迟的非药物强化物的折扣率高低可能更多地取决于即时强化物的质性特征，而较少取决于延迟强化物的数量。
