Parrish, A.E., James, B.T., Rossettie, M.S., Smith, T., Otalora-Garcia, A., & Beran, M.J. (2018). Investigating the depletion effect: Self-control does not waiver in capuchin monkeys. Animal Behavior and Cognition, 5(1), 118-138. https://doi.org/10.26451/abc.05.01.09.2018

The ego-depletion hypothesis states that self-control diminishes over time and with exertion. However, there is mixed evidence among human adult and comparative studies as to whether such depletion occurs. It is an important issue, given that evidence for or against this hypothesis could have implications for remediation efforts with individuals who show high impulsivity and low self-control. In a study of potential depletion effects on self-control, capuchin monkeys were presented with two consecutive self-control tasks back-to-back within sessions. Monkeys first completed the accumulation task, in which they were presented with food items one-by-one until the subject retrieved and ate the accumulating items, at which point no more food would be delivered. This required continual inhibition of food retrieval in the face of an increasingly desirable reward. Then, monkeys completed a food exchange task with exchange combinations that either decreased or increased in food quality. Self-control was required in foregoing eating an immediately available food for a potentially better reward later in the trial. Individual differences in accumulation performance were observed, but no depletion effects were seen in the monkeys’ exchange performance. Next, monkeys were presented with task order counterbalanced across individuals. No order effects were observed in the monkeys’ performance on either self-control task. Monkeys’ exchange performance was not significantly correlated with accumulation performance in either experiment. These results indicate no depletion effects and that these tasks may not be related in terms of underlying mechanisms that support self-control performance, even though at face value both require inhibition of eating available food.

Self-control; Ego-depletion; Capuchin monkey; Accumulation task; Food exchange; Delay of gratification