Monkeys can learn symbols

Ah, crap, now I have to change another lecture slide… No, this is cool. From Science Daily, The Symbolic Monkey? Animals Can Comprehend And Use Symbols, Study Of Tufted Capuchins Suggests discusses research that appeared in PLoS ONE. Some theorists refer to humans as ‘the symbolic species,’ but like so many distinctions that used to seem so clearly differentiating of ‘human nature,’ we find that the distinction is more of degree than kind. For example, studies of chimpanzees and gorillas taught manual or token languages have shown that great apes are capable of using symbols to communicate; whether or not monkeys could was less clear.

In this experiment, the researchers used the equivalent of ‘food standard’ money with monkeys to see how they understood the value of tokens which were equated to different types of food. The Science Daily article explained:

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.

Turns out that the monkeys’ choices were ‘transitive,’ that is, they demonstrated the same preferences whether they were transacting in real food or in intrinsically meaningless tokens that represented the food. It turned out that tufted capuchins preferred Cheerios to parmesan cheese (dumb bastards); however, when transacting in tokens, the rate of exchange between foods became more pronounced. They held out for more parmesan cheese for their Cheerios when using tokens; in actual food, the exchange rate was one Cheerio for two pieces of cheese, but this inflated to one Cheerio for four pieces of cheese (for example) in tokens.


The end of the article in Science Daily explains the pattern of shifting ‘relative value’ between different sorts of foods when tokens were transacted in place of actual food.

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.

I also found the account of the historical emergence of abstract symbolic systems among humans a nice complement to the discussion of capuchins’ difficulties with abstraction (the inflation of relative values). As the authors note, the human achievement of full abstracted written (or engraved) symbols took quite a bit of time, even though markings were being used on containers for several millennia beforehand. I found that the contrast with archaeological evidence for human abstraction to be a real corrective to the tendency to over-exaggerate the differences between humans’ cognitive achievements and those of other animals. In fact, it took a very long time and socially preserved techniques for humans to develop their own ability to manipulate abstract symbols.

References

Addessi, Elsa, Alessandra Mancini, Lara Crescimbene, Camillo Padoa-Schioppa, and Elisabetta Visalberghi. 2008. Preference Transitivity and Symbolic Representation in Capuchin Monkeys (Cebus apella). PLoS One 3(6): e2414 DOI: 10.1371/journal.pone.0002414

Public Library of Science (2008, June 11). The Symbolic Monkey? Animals Can Comprehend And Use Symbols, Study Of Tufted Capuchins Suggests. ScienceDaily. Retrieved June 12, 2008, from http://www.sciencedaily.com /releases/2008/06/080610212404.htm

2 thoughts on “Monkeys can learn symbols

  1. Great post, Greg. I am reminded of some research I read in grad school (can’t remember the citation, sorry) where researchers were asking chimps to do addition or something like that, either with symbols or with actual food. The chimps did great with the symbols. With the food, they just got pissed at the researcher for not giving up the good stuff immediately. Symbols help!

    While trying to track down that reference, I did run across some neat recent research.

    Chimps trying to barter and the evolution of social wealth: http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0001518

    Chimp delay of gratification: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T2J-4KJ6KMB-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=346a7166582801ed022ea0defbd47747

    Chimps using self-distraction to deal with impulsivity: http://www.ncbi.nlm.nih.gov/pubmed/17716966

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