Anything for a Cheerio: Brown Capuchins (\u3cem\u3eSapajus [Cebus] apella\u3c/em\u3e) Consistently Coordinate in an Assurance Game for Unequal Payoffs

Unequal outcomes disrupt cooperation in some situations, but this has not been tested in the context of coordination in economic games. To explore this, we tested brown capuchins (Sapajus [Cebus] apella) on a manual version of the Stag Hunt (or Assurance) Game, in which individuals sequentially chose between two options, Stag or Hare, and were rewarded according to their choices and that of their partner. Typically, coordination on Stag results in an equal highest payout, whereas coordinating on Hare results in a guaranteed equal but lower payoff and uncoordinated play results in the lowest payoff when playing Stag. We varied this structure such that one capuchin received double the rewards for the coordinated Stag outcome; thus, it was still both animals\u27 best option, but no longer equally rewarding. Despite the inequality, capuchins coordinated on Stag in 78% of trials, and neither payoff structure nor their partner\u27s choice impacted their decision. Additionally, there was no relationship between self-scratching, a measure of stress in capuchins, and choices. After completing the study, we discovered our reward, cheerios, was sufficiently valuable that in another study, capuchins never refused it, so post hoc we repeated the study using a lower value reward, banana flavored pellets. Capuchins completed only 26% of the pellet trials (compared to 98% with cheerios), constraining our ability to interpret the results, but nonetheless the monkeys showed a decrease in preference for Stag, particularly when they received fewer rewards for the coordinated Stag outcome. These results reinforce capuchins\u27 ability to find coordinated outcomes in the Stag Hunt game, but more work is needed to determine whether the monkeys did not mind the inequality or were unwilling to sacrifice a highly preferred food to rectify it. In either case, researchers should carefully consider the impact of their chosen rewards on subjects\u27 choices

Investigating the depletion effect: Self-control does not waiver in capuchin monkeys

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