Blurred lines or clear boundaries? Synchrony and social dominance shape domain-specific self-other processing

Synchronous behaviour is widespread across social species and is a common feature of human social interaction. Prior research demonstrates that synchrony can alter self-other processing, yet findings are inconsistent, potentially due to task differences and individual variability. In this preregistered study (54 dyads), we examined whether synchronous finger tapping influences self-other cognition across three domains: episodic memory, source memory, and emotion. Synchrony increased source memory performance but did not affect item memory. In contrast, synchrony heightened emotional egocentric bias, suggesting that synchrony can sharpen self-other differentiation in memory while increasing reliance on one's own affective state when inferring others' emotions. Social dominance moderated certain effects. Dyads with higher combined dominance exhibited stronger synchrony, and dominant individuals showed greater egocentric responding in memory tasks, maintaining a self-referential bias in source memory after synchronous movement. These findings highlight domain-specific consequences of synchrony and the importance of interpersonal traits in shaping synchrony outcomes.