Interpersonal Synchronization of Autonomic Physiology via Mere Visual Contact.

Interpersonal physiological synchrony (IPS)-the temporal alignment of autonomic physiological signals-is emerging as a prominent feature of social interaction. IPS can predict complex social phenomena such as relationship quality or social bonding. Yet, the origins of IPS remain poorly understood. Here, we investigated whether and how IPS can emerge spontaneously through mere visual contact. Thirty-eight dyads of familiar participants were asked to face each other without speaking or making coverbal gestures. IPS was measured using four autonomic signals-heart rate, skin conductance, respiration rate, and pupil diameter-and quantified as the Pearson correlation between dyad members' signals. We found that visual contact was sufficient to synchronize all physiological signals in real dyads, compared with chance-level synchrony in surrogate dyads. Notably, heart rate and pupil diameter IPS were particularly vision-dependent, showing significant reductions when visual contact was prevented. Furthermore, examining the link between IPS and spontaneous social cues revealed that heart rate IPS co-occurred with synchronized body movements, whereas pupil diameter IPS co-occurred with synchronized smiling. These findings show that IPS can emerge spontaneously through mere visual contact and is linked to the exchange of social cues. They position IPS as a robust, self-organizing phenomenon that occurs naturally in social interactions.