REACTIONS TO (IN) EQUALITY IN CAPUCHIN MONKEYS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Social emotions guide human reactions to the efforts, gains, and losses of others. Reactions such as envy, retaliation, and punishment, are sometimes seen as irrational, but may have evolved to promote cooperation. The present study seeks to determine the same reactions in a large-brained, highly cooperative primate, the capuchin monkey (Cebus apella). In previous research these monkeys reacted negatively if a partner received a better reward for equal or less effort. The study addresses the degree to which monkeys monitor the efforts and pay-offs of others, and how they react to (un)equal reward division. Available is a colony of 30 capuchins in an indoor/outdoor enclosure, trained for temporary separation for testing. Monkeys will pull in a tray that rewards their partner at the same time that it rewards themselves. An individual's pulling activity is expected to decline if the partner's rewards substantially exceed those for itself. Females are expected to be more sensitive to reward division than males. This sex difference is tested in two further paradigms, one that measures the feeding speed of two monkeys eating side by side from different foods. Second, in a task of imitation, in which food rewards play a role.