Data from: Rhesus macaques use probabilities to predict future events

Humans can use an intuitive sense of statistics to make predictions about uncertain future events, a cognitive skill that underpins logical and mathematical reasoning. Recent research shows that some of these abilities for statistical inferences can emerge in preverbal infants and non-human primates such as apes and capuchins. An important question is therefore whether animals share the full complement of intuitive reasoning abilities demonstrated by humans, as well as what evolutionary contexts promote the emergence of such skills. Here, we examined whether free-ranging rhesus macaques (Macaca mulatta) can use probability information to infer the most likely outcome of a random lottery, in the first test of whether primates can make such inferences in the absence of direct prior experience. We developed a novel expectancy-violation looking time task, adapted from prior studies of infants, in order to assess the monkeys' expectations. In Study 1, we confirmed that monkeys (n = 20) looked similarly at different sampled items if they had no prior knowledge about the population they were drawn from. In Study 2, monkeys (n = 80) saw a dynamic 'lottery' machine containing a mix of two types of fruit outcomes, and then saw either the more common fruit (expected trial) or the relatively rare fruit (unexpected trial) fall from the machine. We found that monkeys looked longer when they witnessed the unexpected outcome. In Study 3, we confirmed that this effect depended on the causal relationship between the sample and the population, not visual mismatch: monkeys (n = 80) looked equally at both outcomes if the experimenter pulled the sampled item from her pocket. These results reveal that rhesus monkeys spontaneously use information about probability to reason about likely outcomes, and show how comparative studies of nonhumans can disentangle the evolutionary history of logical reasoning capacities.

人类可借助直观统计感知对不确定的未来事件作出预测，这一认知能力是逻辑与数学推理的基础。近期研究表明，部分此类统计推断能力可在前语言婴儿以及猿类、卷尾猴等非人灵长类动物身上显现。因此，一个核心问题随之产生：动物是否具备人类所展现出的全部直观推理能力，以及何种进化背景推动了此类技能的出现？
本研究针对自由活动的恒河猴（Macaca mulatta）展开实验，这是首个检验灵长类动物在无直接先前经验的情况下能否进行此类推断的研究。我们改编自过往针对婴儿的研究，开发了一种全新的违背预期注视时长任务，用以评估猴子的预期。
在实验1中，我们证实：若猴子（n=20）不了解其所抽取样本的来源总体，其对不同样本项目的注视时长无显著差异。
实验2中，猴子（n=80）观察到一台动态“抽奖装置”，其中包含两种混合的水果奖励，随后装置掉落的要么是更常见的水果（预期试次），要么是相对稀有的水果（非预期试次）。我们发现，当猴子目睹非预期结果时，其注视时长更长。
实验3证实，该效应取决于样本与总体之间的因果关联，而非视觉匹配度的差异：若实验者从口袋中取出样本项目，猴子（n=80）对两种结果的注视时长无显著差异。
本研究结果表明，恒河猴会自发利用概率信息推理潜在结果，同时也展示了非人灵长类的比较研究如何厘清逻辑推理能力的进化历程。