Differential Responding by Rhesus Monkeys (Macaca mulatta) and Humans (Homo sapiens) to Variable Outcomes in the Assurance Game

Behavioral flexibility in how one responds to variable partner play can be examined using economic coordination games in which subjects play against a variety of partners and therefore may need to alter their behavior to produce the highest payoff. But how do we study this behavioral flexibility once players have settled on a response? Here, we investigated how responding by rhesus monkeys (Macaca mulatta) and humans (Homo sapiens) playing a computerized single-player version of a coordination game, the Assurance game, changed as a function of the variable responses (Stag/Hare) generated by multiple simulations (SIMs). We were interested in whether individuals could track and differentially respond to changing frequencies of Stag and Hare play by the SIMs, especially with regard to the payoff dominant (Stag-Stag) outcome, something that could not be done with real partners as they quickly settled on the Stag response. For both monkeys and humans, there was a linear relationship between proportion of Stag play by the subject and the likelihood of the Stag choice by the SIM such that both species increased their use of Stag as the SIM increased its use of the Stag response. However, humans more closely matched their proportion of Stag responses to that of the SIM, whereas monkeys adopted a different, but equally effective, strategy of exploiting the higher-paying Stag alternative. These results suggest that monkeys and humans demonstrate sensitivity to a dynamic game environment in which they encounter variable contingencies for the same response options, although they may employ different strategies to maximize reward.