Emotion contagion and physiological synchrony: The more intimate relationships, the more contagion of positive emotions.

The study aimed to explore how interpersonal closeness (friends vs. strangers) and emotion type (positive vs. negative) influenced emotion contagion and physiological synchrony between interacting partners. Twenty-eight friend dyads (n = 56) and 29 stranger dyads (n = 58) participated in an emotion contagion laboratory task. In each dyad, one participant, the 'sender', was randomly asked to watch a film clip (neutral, positive, or negative), while their partner, the 'observer' passively observed the sender's facial expressions. Participants' electrocardiograms (ECG) and facial electromyography (EMG) signals were recorded using the BIOPAC system. Results revealed that observing the sender's facial expressions led to the observer's spontaneous mimicry and emotional contagion, accompanied by enhanced physiological synchrony between interacting partners. In the positive emotion condition, the observers reported more positive emotions and displayed stronger zygomaticus major activity in friend dyads than in stranger dyads. Greater physiological synchrony (heart rate and heart rate variability) between interacting partners was also observed in friend dyads than in stranger dyads in the positive emotion condition. These results indicate that positive emotion contagion is more likely to occur between close partners than negative emotion contagion.