This research program focuses on the self-control behavior of nonhuman primates. Here, we use delay of gratification tasks in which animals can obtain a more preferred or larger reward by waiting to make a response whereas they obtain a smaller or lesser preferred reward if they make that response. In the most recent studies, we have used a technique in which food items accumulate as long as an animal inhibits consumption of those items. Thus, the longer the animal waits to eat the food items that are accessible, the more food items it can acquire. This rather simple technique has provided compelling evidence that chimpanzees show excellent delay of gratification (sometimes for periods in excess of 10 minutes with very highly preferred food accumulating in front of them). Even rhesus monkeys, traditionally viewed as a highly impulsive species, show some success with this task, and recent projects with a new apparatus, the rotating tray task, has shown that capuchin monkeys with very poor delay of gratification skills can improve when given that task. We also have examined the relation between attentional allocation either to the food items or to other available stimuli and delay maintenance (continued inhibition of the impulsive response). For children, attention to the reward is highly detrimental to delay maintenance, but this appears not to be true for chimpanzees. In some cases, attention to the food items may even facilitate greater delay maintenance, and so we continue to probe this relation as well as other aspects of self-control in these species. For example, we have shown that chimpanzees will use self-distraction to help aid delay of gratification, as in the photo at left where Sherman is looking through a magazine during the delay interval.  This research is supported by the National Institute of Child Health and Human Development (HD-060563). To see a story about this ongoing research, click here. 

Dr. Beran wrote a book about much of his research, and that of others, called Self-Control in Animals and People. You can find it here.

Selected Publications:

Beran, M. J., & Hopkins, W. D. (2018). Self-control in chimpanzees relates to general intelligence. Current Biology, 28, 574-579. 

Parrish, A. E., James, B. T., Rossettie, M. S., Smith, T. R., Otalora-Garcia, A., & Beran, M. J. (2018). Investigating the depletion effect: Self-control does not waiver in capuchin monkeys. Animal Behavior and Cognition, 118-138.

Beran, M. J., James, B. T., Whitham, W., & Parrish, A. E. (2016). Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task. Journal of Experimental Psychology: Animal Learning and Cognition, 42, 347-358.

Beran, M. J., Perdue, B. M., Rossettie, M. S., James, B. T., Whitham, W., Walker, B., Futch, S. E., & Parrish, A. E. (2016). Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task.  Behavioural Processes, 129, 68-79.  

Beran, M. J., Rossettie, M. S., & Parrish, A. E. (2016). Trading up: Chimpanzees (Pan troglodytes) show self-control through their exchange behavior. Animal Cognition, 19, 109-121. 

Parrish, A. E., Emerson, I. D., Rossettie, M. S., & Beran, M. J. (2016). Testing the ego-depletion hypothesis among capuchin monkeys: Does glucose boost self-control? Behavioral Sciences, 6, 16.

Perdue, B. M., Bramlett, J. L., Beran, M. J., Evans, T. A., Paglieri, F., McIntyre, J. M, Addessi, E., & Hopkins, W. D. (2014). Chimpanzees (Pan troglodytes) can wait, when they choose to: A study with the hybrid delay task.  Animal Cognition, 17, 197-205. 

Evans, T. A., & Beran, M. J. (2015). Waiting for what comes later: Capuchin monkeys show self-control even for nonvisible delayed rewards. Animal Cognition, 18, 1105-1112.