Capuchin monkeys can appreciate the purchasing power of tokens such as poker chips: at ISTC this is one of the most recent findings of the Unit of Cognitive Primatology (UCP).
Despite 35 million years of independent evolution, capuchin monkeys are a valuable model to investigate the development of human traits, since they show many striking analogies with us in terms of encephalization index, lifespan, omnivorous diet, manipulative skills and tool use. Recently, researchers started to investigate capuchin symbolic competence by using tokens, inherently non-valuable objects that acquire an arbitrary value upon exchange with the experimenters.
At ISTC the Unit of Cognitive Primatology (UCP) led an experiment showing that capuchins, like us, can understand the symbolic value of an otherwise mundane object. The monkeys grasp this "money" concept despite the fact that they are so evolutionarily distant from humans.
UCP team trained the capuchins to associate valueless tokens of different shapes and sizes with specific foods. A poker chip, for example, represented dried apricot, and brass hooks represented Parmesan cheese. Then the monkeys were presented with a choice of two trays, each containing a piece, or pieces, of one of three different foods, labelled A, B and C. The foods were selected, according to the established tastes of the individual monkeys, so that A was nicer than B, which was nicer than C. In the test with real food, the monkeys chose one piece of A over two pieces of B; and would choose one piece of B over two pieces of C. The effect continued so that they might choose one piece of A, their favourite food, over four pieces of less tempting C. They were then offered a similar test, but with the trays loaded with tokens representing the different foods. The monkeys responded in the same way – for example choosing one A token over two B tokens. This shows that the same reasoning was used for both tasks. Capuchin monkeys can therefore use tokens to "buy" their favourite food, choosing the most convenient solutions. Just like us.
Contact: Elsa Addessi
ISTC Group: Unit of Cognitive Primatology
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.
Addessi, E., Crescimbene, L. & Visalberghi, E. 2007. Do capuchin monkeys (Cebus apella) use tokens as symbols? Proceedings of the Royal Society of London, Series B, 274:2579–2585.
Addessi, E. & Rossi, S. 2011. Tokens improve capuchin performance in the reverse–reward contingency task. Proceedings of the Royal Society of London, Series B, 278:849-854.