Facial expressions as honest signals of cooperative intent in a one-shot anonymous Prisoner's Dilemma game

Previous research has posited that facial expressions of emotion may serve as honest signals of cooperation. Although findings from several empirical studies support this position, prior studies have not used comprehensive and dynamic measures of facial expression as potential predictors of behaviorally defined cooperation. The authors investigated (a) specific positive and negative facial actions displayed among strangers immediately following verbal promises of commitment within an unrestricted acquaintance period and (b) anonymous, behaviorally defined decisions of cooperation or defection in a one-shot, two-person Prisoner's Dilemma game occurring directly following the acquaintance period. The Facial Action Coding System [Ekman P. & Friesen W.V. (1978). Facial Action Coding System. Palo Alto, CA: Consulting Psychology Press] was used to measure affect-related facial actions. It was found that facial actions related to enjoyment were predictive of cooperative decisions within dyads; additionally, facial actions related to contempt were predictive of noncooperative decisions within dyads. Furthermore, and consistent with previous works, participants were able to accurately predict their partner's decisions following the acquaintance period. These results suggest that facial actions may function as honest signals of cooperative intent. These findings also provide a possible explanation for the association between subjective affective experience and facial expression that advances understanding of cooperative behavior.