SELF-CONTROL IN THE MONKEY MACACA-FASCICULARIS

Two experiments tested two cynomolgus monkeys' self-control-choice of a longer, more delayed reinforcer over a shorter, less delayed reinfor cer. In Experiment 1, subjects exhibited significant self-control in a procedure in which reinforcer amounts and delays were held constant t hroughout a condition. In Experiment 2, subjects exhibited significant ly greater sensitivity to variation in reinforcer amount than to varia tion in reinforcer delay in a procedure in which the reinforcer delay associated with the self-control alternative was adjusted until each m acaque was indifferent between the two alternatives. Both experiments indicated that, in laboratory paradigms in which humans show self-cont rol and pigeons and rats show impulsiveness, macaques show self-contro l. These results are inconsistent with the hypothesis that species dif ferences in self-control are a function of language ability or of spec ific types of prior training. The results are consistent with the hypo thesis that species differences in self-control are related to the rat io of brain size to body weight (a possible indicator of general cogni tive ability) or to shared phylogeny.