Emotional correlates of probabilistic decision making in tufted capuchin monkeys (Sapajus spp.)

Abstract

In humans, emotions play a fundamental role in decision making. Although there is considerable evidence that nonhuman animals exhibit emotions, studies on how emotional responses affect their choice behaviour are scant. We tested tufted capuchin monkeys in a probabilistic choice task, in which subjects were repeatedly offered a choice between a safe option (corresponding to four food units) and a risky option (corresponding to either one or seven food units). The study included three conditions that differed in the probability of receiving the larger outcome when choosing the risky option. We evaluated whether capuchins anticipated that they may experience negative consequences from their choices by scoring latency to choose, scratching and alarm vocalizations before they made their choices. Moreover, we assessed whether capuchins exhibited emotional responses to different decision outcomes by scoring scratching, alarm vocalizations, banging, and switching after the choice outcomes were revealed. We also assessed whether capuchins' motivation to choose the risky option and emotional responses were modulated by the probability of ‘winning’ and whether the emotional responses experienced after receiving the choice outcomes affected their subsequent decisions. Capuchins scratched more before making their choices than after choice outcomes were revealed, whereas alarm vocalizations showed the opposite pattern. Thus, the capuchins seemed more sensitive to the conflict experienced when deciding which option to choose than to the frustration of receiving an undesired outcome. The inconsistent pattern of scratching and alarm vocalizations suggests that these behaviours indicate different emotional states. Capuchins showed more emotional responses and attempts at switching their initial choice after a one-item outcome than a four-item or a seven-item outcome, suggesting that they experienced regret-like emotions. The lack of a negative impact of receiving one-item outcomes on capuchins' subsequent choices may support the view that emotional responses have a coping function, but this hypothesis remains to be demonstrated.