Sources of Facial Expression Synchrony

Dyadic synchrony—the temporal coordination of behavior and emotions between individuals—is a key aspect of social interactions. Although synchrony in social interactions has been extensively studied, researchers continue to investigate the underlying factors and processes that contribute to this phenomenon of dyadic synchrony. We argue that synchrony in social interactions could potentially emerge from two sources: (1) people are responding to each other's expressions or (2) people are responding to a shared task. It is also possible that synchrony results from a combination of both these factors. The present study investigated the sources of dyadic synchrony during an iterated prisoner's dilemma (IPD) task. We examined two conditions: a still condition, where dyads only saw a still image of their partner, and a video condition, where dyads had real-time visual access to their partner's facial reactions. We assessed synchrony using Dynamic Time Warping in real dyads and randomly paired dyads. Our findings revealed that synchrony was present in real interactions even without visual cues, suggesting that shared experiences of reacting to a joint outcome contribute to synchrony. The ability to see the partner's facial reaction in the video condition further enhanced synchrony, particularly when dyad members' decisions were not aligned. These results underscore the interplay between shared experiences and visual cues in driving dyadic synchrony during interactive social situations, providing valuable insights into the mechanisms underlying social coordination and alignment in cooperative and competitive contexts.