Heart rate synchrony in minimal social interactions in relation to mimicry

Humans align their physiology during social encounters, but the mechanisms driving this autonomic coupling remain unclear. Mimicry has been proposed as a driver, yet existing evidence is largely correlational and limited to precisely matched movements. We causally tested whether two forms of mimicry, copying a partner’s choices or motor actions, can induce heart rate synchrony during a controlled, non-verbal art selection task. In the Choice group (21 dyads), a confederate mimicked (or not) the participant’s picture choice but not their hand action. In the Motor group (20 dyads), a confederate mimicked (or not) the participant’s right-hand movements but chose from a different picture pair. Dyadic heart rate synchrony was quantified using mixed-effects models of trial-level heart rate fluctuations. Partners’ heart rates covaried within and across trials, but neither the presence nor the type of mimicry altered this coupling. After modelling temporal trends and comparing real dyads with time-matched pseudo-dyads, the observed synchrony was largely explained by shared task and timing dynamics rather than dyad-specific physiological alignment. Thus, instructed mimicry alone is insufficient to elicit dyad-specific cardiac coupling in minimal, tightly structured interactions. More broadly, these results caution against interpreting physiological synchrony as interpersonal alignment without accounting for shared temporal structure.