Abstract
Humans and nonhuman great apes share a sense for intuitive statistics, making intuitive probability judgments based on proportional information. This ability is of tremendous importance, in particular for predicting the outcome of events using prior information and for inferring general regularities from limited numbers of observations. Already in infancy, humans functionally integrate intuitive statistics with other cognitive domains, rendering this type of reasoning a powerful tool to make rational decisions in a variety of contexts. Recent research suggests that chimpanzees are capable of one type of such cross-domain integration: The integration of statistical and social information. Here, we investigated whether apes can also integrate physical information into their statistical inferences. We tested 14 sanctuary-living chimpanzees in a new task setup consisting of two “gumball machine”-apparatuses that were filled with different combinations of preferred and non-preferred food items. In four test conditions, subjects decided which of two apparatuses they wanted to operate to receive a random sample, while we varied both the proportional composition of the food items as well as their spatial configuration above and below a barrier. To receive the more favorable sample, apes needed to integrate proportional and spatial information. Chimpanzees succeeded in conditions in which we provided them either with proportional information or spatial information, but they failed to correctly integrate both types of information when they were in conflict. Whether these limitations in chimpanzees' performance reflect true limits of cognitive competence or merely performance limitations due to accessory task demands is still an open question.
Highlights
Intuitive statistical reasoning is the capacity to make intuitive probabilistic inferences based on relations between populations, sampling procedures and resulting samples
These studies demonstrated that pre-verbal infants reason from population to sample, but they take into account social and physical variables when drawing statistical inferences
Does the failure of chimpanzees to reason about physical information when drawing statistical inferences imply that apes are not capable of domain-general statistical inference? Or do these negative findings reflect mere performance limitations, rather than competence limits? We will discuss five possible explanations that might account for the apes’ poor performance in the crucial test conditions, in which proportional information and physical information were conflicted
Summary
Intuitive statistical reasoning is the capacity to make intuitive probabilistic inferences based on relations between populations, sampling procedures and resulting samples. When the same biased experimenter sampled blindly, infants expected the sample to be of the majority type of the population (Xu & Denison, 2009) These findings demonstrated that infants flexibly considered intuitive psychological knowledge to judge the sampling conditions and drew according statistical inferences. Infantslooking times followed a graded pattern: when the occlusion duration was very short, infants seemed to judge the situation based on the spatial arrangement immediately before the occlusion and expected that object closest to the opening to exit, regardless of whether it was of the minority or majority type. Infants integrated information about the ratio of objects, their physical arrangement and occlusion time to judge the outcome of an event Together, these studies demonstrated that pre-verbal infants reason from population to sample, but they take into account social and physical variables when drawing statistical inferences. The ability to transfer and combine information across different domains is, aside from context and stimulus independence, one source of evidence for domaingenerality
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