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Negative Behavioral Contrast in Capuchin Monkeys (Sapajus sp.)


A capuchin monkey will accept a preferred food in exchange for tokens if a conspecific also exchanges tokens for the preferred food; but he will reject a less-preferred food if the conspecific exchanges tokens for preferred food. These rejections are usually interpreted as a case of an inequity aversion based on a precursor of a sense of justice. An alternative hypothesis proposes that it is the contrast between the types of food reinforcement experienced by the subject throughout the task that affects the reinforcing function of the less-preferred food. The present study tested this hypothesis with three conditions. Capuchin monkeys received cucumbers (the less-preferred food) as the reinforcer in a token-exchange task during the first and third conditions, and received grapes (the preferred food) in the second condition. The difference in the proportions of acceptances between the first and the third conditions provided evidence of negative contrast in this species, a type of contrast that can at least partially account for the rejections documented in the inequity-aversion literature.

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  1. At first, the grapes had their seeds on, but once we noticed that one of the monkeys (Tico) took off the seeds before eating, we started removing all the seeds from the grapes before running the experimental sessions.


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We thank Edilson Pastana, Anna Carolina Damasceno and the members of the Primate Experimental School for their cooperation. APR and ST conducted the experiment under the supervision of MPC and were supported by master’s studentships from the National Council for Scientific and Technological Development (CNPq) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), respectively.

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The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.


The first author was supported by a master’s studentship from the National Council for Scientific and Technological Development (CNPq) and the third author by a master’s studentship from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). The authors declare that they have no other conflicts of interest.

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Correspondence to Marilia Pinheiro de Carvalho.

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All applicable national and institutional guidelines for the care and use of animals were followed. The procedures performed in this study with capuchin monkeys (Sapajus sp.) were in accordance with the ethical standards of the Primate Experimental School and the Animal Ethics Committee of the Federal University of Pará, Brazil (CEPAE 040-2015).

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Table 1 Individual rejection proportions throughout the token exchange task. The gray areas stand for the cucumber conditions and the white areas stand for the grape condition

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Rocha, A.P., de Carvalho, M.P., Tavares, S. et al. Negative Behavioral Contrast in Capuchin Monkeys (Sapajus sp.). Psychol Rec 71, 133–141 (2021).

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  • Negative contrast
  • Capuchin monkeys (Sapajus sp.)
  • Inequity aversion
  • Frustration