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Monkeys form expectations for outcomes based on interactions with human experimenters. Not only do they anticipate receiving rewards which the experimenter indicates, but capuchin monkeys, a cooperative new world monkey species, apparently anticipate rewards based on what the experimenter has given to their partner. However, this could be due to subjects responding to either outcomes or experimenters. Here we examine whether capuchin monkeys will continue to interact with human experimenters who are occasionally unreliable. We tested ten monkeys with a series of familiar human experimenters using an exchange task. The experimenters had never before participated in exchange studies with these monkeys, hence the monkeys learned about their behavior during the course of testing. Occasionally experimenters were unreliable, failing to give a reward after the monkey returned the token. We found that monkeys did recognize these interactions as different, responding much more quickly in trials following those which were non-rewarded than in other situations with the same experimenter. However, subjects did not change their preference for experimenters when given the opportunity to choose between the unreliable exchanger and another exchanger, nor did subjects learn to prefer reliable experimenters from watching other monkeys’ interactions. Instead, subjects returned the tokens to the same location from which they received it. These results indicate that capuchin monkeys may not be sensitive to isolated instances in which experimenters are unreliable, possibly because of a strong bias to returning the token to the location from which it was donated.


This article was originally published in the International Journal of Primatology. Copyright © 2009 Springer.

The post-peer-reviewed version is available here with the permission of the author.

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