Solomon Rebecca Brana, Conover Kent, Shizgal Peter
Centre for Studies in Behavioural Neurobiology / Groupe de recherche en neurobiologie comportementale, Department of Psychology, Concordia University, Montréal, Québec, Canada.
PLoS One. 2017 Aug 25;12(8):e0182120. doi: 10.1371/journal.pone.0182120. eCollection 2017.
Pursuit of one goal typically precludes simultaneous pursuit of another. Thus, each exclusive activity entails an "opportunity cost:" the forgone benefits from the next-best activity eschewed. The present experiment estimates, in laboratory rats, the function that maps objective opportunity costs into subjective ones. In an operant chamber, rewarding electrical brain stimulation was delivered when the cumulative time a lever had been depressed reached a criterion duration. The value of the activities forgone during this duration is the opportunity cost of the electrical reward. We determined which of four functions best describes how objective opportunity costs, expressed as the required duration of lever depression, are translated into their subjective equivalents. The simplest account is the identity function, which equates subjective and objective opportunity costs. A variant of this function called the "sigmoidal-slope function," converges on the identity function at longer durations but deviates from it at shorter durations. The sigmoidal-slope function has the form of a hockey stick. The flat "blade" denotes a range over which opportunity costs are subjectively equivalent; these durations are too short to allow substitution of more beneficial activities. The blade extends into an upward-curving portion over which costs become discriminable and finally into the straight "handle," over which objective and subjective costs match. The two remaining functions are based on hyperbolic and exponential temporal discounting, respectively. The results are best described by the sigmoidal-slope function. That this is so suggests that different principles of intertemporal choice are involved in the evaluation of time spent working for a reward or waiting for its delivery. The subjective opportunity-cost function plays a key role in the evaluation and selection of goals. An accurate description of its form and parameters is essential to successful modeling and prediction of instrumental performance and reward-related decision making.
追求一个目标通常会排除同时追求另一个目标的可能性。因此，每一项排他性活动都伴随着一种“机会成本”：即放弃的次优活动所带来的收益。本实验在实验室大鼠中估计了将客观机会成本映射为主观机会成本的函数。在一个操作性条件反射箱中，当杠杆被按下的累计时间达到一个标准持续时间时，给予奖励性脑电刺激。在此持续时间内放弃的活动的价值就是电刺激奖励的机会成本。我们确定了四个函数中的哪一个最能描述客观机会成本（表示为杠杆按下所需的持续时间）如何转化为主观等价物。最简单的情况是恒等函数，它将主观和客观机会成本等同起来。这个函数的一个变体称为“sigmoidal斜率函数”，在较长持续时间时收敛于恒等函数，但在较短持续时间时与之偏离。sigmoidal斜率函数呈曲棍球棒的形状。平坦的“棒刃”表示一个机会成本在主观上相等的范围；这些持续时间太短，无法替代更有益的活动。棒刃延伸到向上弯曲的部分，在此期间成本变得可区分，最后进入笔直的“手柄”部分，在此客观和主观成本相匹配。剩下的两个函数分别基于双曲线和指数时间贴现。结果用sigmoidal斜率函数描述最为合适。情况既然如此，这表明在评估为获得奖励而工作的时间或等待奖励发放的时间时，涉及到不同的跨期选择原则。主观机会成本函数在目标的评估和选择中起着关键作用。准确描述其形式和参数对于成功建模和预测工具性表现以及与奖励相关的决策至关重要。
