Gambling primates: reactions to a modified Iowa Gambling Task in humans, chimpanzees and capuchin monkeys
Humans will, at times, act against their own economic self-interest, for example, in gambling situations. To explore the evolutionary roots of this behavior, we modified a traditional human gambling task, the Iowa Gambling Task (IGT), for use with chimpanzees, capuchin monkeys and humans. We expanded the traditional task to include two additional payoff structures to fully elucidate the ways in which these primate species respond to differing reward distributions versus overall quantities of rewards, a component often missing in the existing literature. We found that while all three species respond as typical humans do in the standard IGT payoff structure, species and individual differences emerge in our new payoff structures. Specifically, when variance avoidance and reward maximization conflicted, roughly equivalent numbers of apes maximized their rewards and avoided variance, indicating that the traditional payoff structure of the IGT is insufficient to disentangle these competing strategies. Capuchin monkeys showed little consistency in their choices. To determine whether this was a true species difference or an effect of task presentation, we replicated the experiment but increased the intertrial interval. In this case, several capuchin monkeys followed a reward maximization strategy, while chimpanzees retained the same strategy they had used previously. This suggests that individual differences in strategies for interacting with variance and reward maximization are present in apes, but not in capuchin monkeys. The primate gambling task presented here is a useful methodology for disentangling strategies of variance avoidance and reward maximization.
KeywordsPrimate Gambling Risk Iowa Gambling Task Behavioral economics
We thank the animal care and veterinary staff at the Yerkes National Primate Research Center and the Language Research Center for maintaining the health and well-being of the chimpanzees. DP was supported by an American Psychological Association Dissertation Research Award (2011), NIH/NIGMS IRACDA grant K12 GM000680 awarded to Emory University and NSF SES 0847351 awarded to SFB. SFB was funded by NSF CAREER Award SES 0847351, NSF HSD grant SES 0729244 and NSF SES 1123897. At Yerkes, this work was supported by the Living Links Center, Emory’s College of Arts and Sciences and the base grant of the National Center for Research Resources P51RR165 to the YNPRC, currently supported by the Office of Research Infrastructure Programs/OD P51OD11132. The YNPRC is fully accredited by the American Association for Accreditation for Laboratory Animal Care. This research complied with all laws of the United States of America.
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