Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance
Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.
KeywordsDelay of gratification Symbolic stimuli Cebus apella Pan troglodytes Token exchange
We thank Betty Chan, Daniel Hoyle, and Joseph McIntyre for their assistance with data collection. This research was funded by grants HD-38051 and HD-060563 from the National Institute of Child Health and Human Development and grant BCS-0924811 from the National Science Foundation.
- Baumeister RF, Vohs KD (eds) (2004) Handbook of self-regulation: research theory and applications. Guilford Press, New YorkGoogle Scholar
- Beran MJ, Savage-Rumbaugh ES, Pate JL, Rumbaugh DM (1999) Delay of gratification in chimpanzees (Pan troglodytes). Dev Psychobiol 34:119–127. doi: 10.1002/(SICI)1098-2302(199903)34:2<119:AID-DEV5>3.0.CO;2-P PubMedCrossRefGoogle Scholar
- Hopper LM, Essler J, Freeman H, Talbot CF, Lambeth SP, Schapiro SJ, Williams LE, Brosnan SF (in prep) Enough is enough: the effect of the frequency of unequal outcomes on decisions to accept food rewards in four primate speciesGoogle Scholar
- Parrish A, Brosnan SF (in prep) Changing the relative difference in outcomes affects reactions to unequal rewards in capuchin monkeys (Cebus apella)Google Scholar
- Stevens JR, Rosati AG, Heilbronner SR, Mühlhoff N (2011) Waiting for grapes: expectancy and delayed gratification in bonobos. Int J Comp Psychol 24:99–111Google Scholar
- Tobin H, Chelonis JJ, Logue AW (1993) Choice in self-control paradigms using rats. Psychol Rec 43:441–453Google Scholar
- Vlamings PHJM, Uher J, Call J (2006) How the great apes (Pan troglodytes, Pongo pygmaeus, Pan paniscus, and Gorilla gorilla) perform on the reversed contingency task: the effects of food quantity and food visibility. J Exp Psychol Anim Behav Process 32:60–70. doi: 10.1037/0097-7403.32.1.60 PubMedCrossRefGoogle Scholar