Physiological synchrony promotes cooperative success in real-life interactions

Cooperation is pivotal for society to flourish and prosper. To ease cooperation, humans express and read emotions and intentions via explicit signals or subtle reflections of arousal visible in the face. Evidence is accumulating that humans synchronize these nonverbal expressions, as well as the physiological mechanisms underlying them, potentially promoting cooperative behavior. The current study is designed to verify the existence of this putative linkage between synchrony and cooperation. To that extent, 152 participants played multiple rounds of the Prisoner9s Dilemma game in a naturalistic dyadic interaction setting. During one round of games they could see each other, and during a second round they could not. The results showed that when people9s heart rate and skin conductance level aligned, they cooperated more successfully. Interestingly, for skin conductance level synchrony to boost cooperation, face to face contact was essential. The effect of heart rate synchrony on cooperation was context independent. Skin conductance level, but not heart rate, tended to closely correlate with changes in pupil size and we discuss how the pupil might provide a window to partners9 sympathetic arousal. These findings show how unconscious mechanisms guide social behavior and emphasize the importance of studying social processes between rather than within individuals in real-life interactions.