, Volume 24, Issue 2, pp 168-174

Self-control in the monkeymacaca fascicularis


Two experiments tested two cynomolgus monkeys’ self-control—choice of a longer, more delayed reinforcer over a shorter, less delayed reinforcer. In Experiment 1, subjects exhibited significant selfcontrol in a procedure in which reinforcer amounts and delays were held constant throughout a condition. In Experiment 2, subjects exhibited significantly greater sensitivity to variation in reinforcer amount than to variation in reinforcer delay in a procedure in which the reinforcer delay associated with the self-control alternative was adjusted until each macaque was indifferent between the two alternatives. Both experiments indicated that, in laboratory paradigms in which humans show self-control and pigeons and rats show impulsiveness, macaques show self-control. These results are inconsistent with the hypothesis that species differences in self-control are a function of language ability or of specific types of prior training. The results are consistent with the hypothesis that species differences in self-control are related to the ratio of brain size to body weight (a possible indicator of general cognitive ability) or to shared phylogeny.

This research was supported in part by a Grant-in-Aid of Research from Sigma Xi to H.T., and by a grant from the National Science Foundation. We thank R. Reeder, G. Higgins, and R. Chorley for their assistance with the apparatus and software, K. Batsche for his instruction and assistance in handling the subjects and selecting a reinforcer, and L. J. Bird for her assistance in conducting the experiment.
—Accepted by previous editor, Vincent M. LoLordo