Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom
Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom.
J Neurosci. 2019 Apr 10;39(15):2915-2929. doi: 10.1523/JNEUROSCI.1454-18.2018. Epub 2019 Jan 31.
Humans and other primates share many decision biases, among them our subjective distortion of objective probabilities. When making choices between uncertain rewards we typically treat probabilities nonlinearly: overvaluing low probabilities of reward and undervaluing high ones. A growing body of evidence, however, points to a more flexible pattern of distortion than the classical inverse-S one, highlighting the effect of experimental conditions in shifting the weight assigned to probabilities, such as task feedback, learning, and attention. Here we investigated the role of sequence structure (the order in which gambles are presented in a choice task) in shaping the probability distortion patterns of rhesus macaques: we presented 2 male monkeys with binary choice sequences of MIXED or REPEATED gambles against safe rewards. Parametric modeling revealed that choices in each sequence type were guided by significantly different patterns of probability distortion: whereas we elicited the classical inverse-S-shaped probability distortion in pseudorandomly MIXED trial sequences of gamble-safe choices, we found the opposite pattern consisting of S-shaped distortion, with REPEATED sequences. We extended these results to binary choices between two gambles, without a safe option, and confirmed the unique influence of the sequence structure in which the animals make choices. Finally, we showed that the value of gambles experienced in the past had a significant impact on the subjective value of future ones, shaping probability distortion on a trial-by-trial basis. Together, our results suggest that differences in choice sequence are sufficient to reverse the direction of probability distortion. Our lives are peppered with uncertain, probabilistic choices. Recent studies showed how such probabilities are subjectively distorted. In the present study, we show that probability distortions in macaque monkeys differ significantly between sequences in which single gambles are repeated (S-shaped distortion), as opposed to being pseudorandomly intermixed with other gambles (inverse-S-shaped distortion). Our findings challenge the idea of fixed probability distortions resulting from inflexible computations, and points to a more instantaneous evaluation of probabilistic information. Past trial outcomes appeared to drive the "gap" between probability distortions in different conditions. Our data suggest that, as in most adaptive systems, probability values are slowly but constantly updated from prior experience, driving measures of probability distortion to either side of the S/inverse-S debate.
人类和其他灵长类动物共有许多决策偏差，其中包括我们对客观概率的主观扭曲。在不确定奖励之间做出选择时，我们通常会对概率进行非线性处理：高估低概率的奖励，低估高概率的奖励。越来越多的证据表明，与经典的反 S 型相比，扭曲模式更为灵活，突出了实验条件在改变概率权重方面的作用，例如任务反馈、学习和注意力。在这里，我们研究了序列结构（在选择任务中赌博呈现的顺序）在塑造恒河猴概率扭曲模式中的作用：我们向 2 只雄性猴子展示了混合或重复赌博与安全奖励的二进制选择序列。参数建模显示，每种序列类型的选择都受到明显不同的概率扭曲模式的指导：虽然我们在混合赌博安全选择的伪随机 MIXED 试验序列中引出了经典的反 S 型概率扭曲，但我们发现了相反的模式，即 S 型扭曲，在重复序列中。我们将这些结果扩展到没有安全选项的两个赌博之间的二进制选择，并确认了动物做出选择的序列结构的独特影响。最后，我们表明过去经历的赌博价值对未来赌博的主观价值有重大影响，从而在逐次试验的基础上塑造概率扭曲。总的来说，我们的结果表明，选择序列的差异足以改变概率扭曲的方向。我们的生活充满了不确定的、概率性的选择。最近的研究表明，这些概率是如何被主观扭曲的。在本研究中，我们表明，恒河猴的概率扭曲在重复出现的单个赌博的序列（S 型扭曲）中与在其他赌博随机混合的序列（反 S 型扭曲）之间有显著差异。我们的发现挑战了由于计算不灵活而导致的固定概率扭曲的想法，并指出了对概率信息的更即时评估。过去的试验结果似乎推动了不同条件下概率扭曲之间的“差距”。我们的数据表明，与大多数自适应系统一样，概率值会从先前的经验中缓慢但不断地更新，从而将概率扭曲的度量推向 S/反 S 争论的任何一方。
