Public Release:  The symbolic monkey? Token-mediated economic choices in tufted capuchins


From paintings and photographs to coins and credit cards, we are constantly surrounded by symbolic artefacts. The mental representation of symbols - objects that arbitrarily represent other objects - ultimately affords the development of language, and certainly played a decisive role in the evolution of our hominid ancestors. Can other animal species also comprehend and use symbols? Some evidence suggests that apes, our closest relatives, can indeed use symbols in various contexts. However, little is known about the symbolic competence of phylogenetically more distant species.

A study published in this week's PLoS ONE presents evidence of symbolic reasoning in tufted capuchin monkeys, a South-American species that diverged from humans about 35 million years ago. In the experiment, five capuchins engaged in "economic choice" behavior. Each monkey chose between three different foods (conventionally referred to A, B and C), offered in variable amounts. Choices were made in two different contexts. In the "real" context, monkeys chose between the actual foods. In the "symbolic" context, monkeys chose between "tokens" (intrinsically valueless objects such as poker chips) that represented the actual foods. After choosing one of the two token options, monkeys could exchange their token with the corresponding food. The researchers examined whether capuchins' preferences in both real and symbolic contexts satisfy transitivity -- a fundamental trait of rational decision-making, according to which if A is preferred to B, and B is preferred to C, then A must be preferred to C.

Capuchins' choices did satisfy transitivity, both in the real context and in the symbolic context. Capuchins systematically preferred item A to B, item B to C, and item A to C both with tokens and with the actual foods. Hence, their preferences were qualitatively similar in both contexts. Quantitatively, however, expressing choices in the symbolic context increased the value distance between the corresponding foods. For example, when choosing between actual foods, capuchins were indifferent between one Cheerio and two pieces of parmesan cheese, indicating that the value of one Cheerio is equal to two times the value of one piece of parmesan cheese. When choosing between tokens that represented the same foods, the relative value increased - for example, capuchins were indifferent between one Cheerio-token and four parmesan-tokens.

These results indicate that capuchin monkeys can indeed reason about symbols. However, as they do so, capuchins also experience the cognitive burden of symbolic representation, and in this respect they appear to behave similarly to young children. In sum, though capuchins may not achieve adult-human-like symbolic competence, this study demonstrates that animal species relatively distant from humans have undertaken the path of symbolic use and understanding.


This study was conducted at CNR, Institute of Cognitive Sciences and Technologies, Unit of Cognitive Primatology and Primate Center, Rome, Italy. Funded by EU FP6 NEST Programme SEDSU (N°12984).

Elsa Addessi

Citation: Addessi E, Mancini A, Crescimbene L, Padoa-Schioppa C, Visalberghi E (2008) Preference Transitivity and Symbolic Representation in Capuchin Monkeys (Cebus apella). PLoS ONE 3(6): e2414. doi:10.1371/journal.pone.0002414



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Related movies (these movies form part of the published paper and are covered by a Creative Commons Attribution License. Any use should include citation of the authors and paper as the original source):

  • Video S1 - Food condition. Carlotta, a female capuchin, has a choice between one Cheerio (food A, on the left) and three pieces of parmesan cheese (food B, on the right). She selects the three pieces of parmesan cheese by pulling the corresponding tray.
  • Video S5 - Token condition. Carlotta has a choice between one green poker chip (token A, corresponding to one Cheerio, on the left) and three brass hooks (token C, corresponding to one sunflower seed each, on the right). She selects the token A by pulling the corresponding tray.


