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J Comp Psychol. 2018 May;132(2):166-177. doi: 10.1037/com0000106. Epub 2018 Mar 12.

Initial evidence for probabilistic reasoning in a grey parrot (Psittacus erithacus).

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Department of Psychology, Harvard University.
Department of Psychology, Brandeis University.


Research has shown that some forms of inferential reasoning are likely widespread throughout the animal kingdom (e.g., exclusion, in which a subject infers the placement of a reward by eliminating potential alternative sites), but other types of inferential tasks have not been extensively tested. We examined whether a nonhuman might succeed in an experiment based on probabilistic reasoning, specifically, the ability to make inferences about a sample based on information about a population. A Grey parrot (Psittacus erithacus), previously trained to use English labels referentially to identify objects, observed a human researcher deposit 2 different types of items in a 3:1 ratio (e.g., 3 corks and 1 piece of paper) into an opaque bucket. One item was then randomly withdrawn while hidden from the parrot's view. When asked to identify the still-hidden object, the parrot's vocal responses tracked this 3:1 ratio over a large number of trials. Some levels of probabilistic reasoning therefore are not limited to humans, nonhuman primates, or even mammals. (PsycINFO Database Record.

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