title: When maths trumps logic: probabilistic judgements in chimpanzees.
abstract: When searching for hidden food, do chimpanzees take into account both the number of hidden items and the number of potential hiding locations? We presented chimpanzees with two trays, each of them containing a different food/cup ratio and therefore a different likelihood of finding a baited cup among empty alternatives. Subjects' performance was directly influenced by the relative difference (probability ratio (PR)) between the two given probabilities. Interestingly, however, they did not appreciate the special value of a truly safe option (with P = 1.0). Instead, they seemed to 'blindly' rely on the PR between the two options, systematically preferring the more likely one once a certain threshold had been reached. A control condition ruled out the possibility of low-level learning explanations for the observed performance.
authors.affiliation: Department of Developmental and Comparative Psychology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany hanus@eva.mpg.de.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hanus
authors.affiliation: Department of Developmental and Comparative Psychology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany School of Psychology and Neuroscience, University of St Andrews, St Andrews, UK.
authors.forename: Josep
authors.initials: J
authors.lastname: Call
mesh_terms: D000818:Animals; D008433:Mathematics; D002679:Pan troglodytes / Q000523:psychology*; D011336:Probability
keywords: chimpanzees; numerical cognition; probabilities