DOI: 10.5061/dryad.22mv245
title: Data from: Rhesus macaques use probabilities to predict future events

description: 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.
description: De Petrillo & Rosati
 Study 1 (Fruit Preference)Trial data from Study 1
 (fruit preference validation). Key for variable codes included as a
 separate tab in the file.De_Petrillo-Rosati-Study1-FruitPreference-DRYAD.xlsxDe Petrillo & Rosati Study 2 (Probability Inference)Trial data from Study 2 (probability inference). Key for variable codes included as a separate tab in the file.De_Petrillo-Rosati-Study2-ProbabilityInference-DRYAD.xlsxDe Petrillo & Rosati Study 3 (Non-causal Control)Trial data from Study 3 (noncausal control). Key for variable codes included as a separate tab in the file.De_Petrillo-Rosati-Study3-NoncausalControl-DRYAD.xlsxVideo S1: Procedure demonstrations and monkey responseThe video shows the lottery machine task used in all three studies. The first clip shows the Fruit Preference Validation procedure from Study 1 from the monkey's perspective. Here, E1 uses a stick (out of the monkey's view) to rotate the lottery machine; in this study the population of fruit is occluded in this phase. E1 then releases a lemon from the machine to the clear cup below, and says “now” to mark the start of the trial. Each trial then lasts 10 s, and the looking time of the monkey is recorded. The second clip shows the Probability Inference procedure from Study 2. Here, E1 open the curtains and reveals a lemon machine containing a population with a probable likelihood distribution (3:1 distribution of lemons and apples). Then, after rotating the machine, she releases the expected outcome (a lemon). The third clip shows the Non-causal control procedure from Study 3. E1 opens the curtains and reveals again a lemon machine, but this time it contains a population with a possible likelihood distribution (only one type of fruit is present). After rotating the cube, E1 visibly pulls the impossible (unexpected) outcome (an apple) from her pocket and then places it into the container above the cube. The final clip shows an example of the monkey's looking response in the task.Video S1.mp4