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 evidence is largely correlational and limited to precisely matched movements. We causally tested whether two mimicry forms, copying a partner’s choices or motor actions, can induce heart rate synchrony in 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. Electrocardiograms were recorded continuously from both partners, and heart rate synchrony was quantified by modelling trial-level heart rate fluctuations with mixed-effects models. Dyads' heart rates were strongly coupled by trial and trial (n - 1), but neither the presence nor the type of mimicry altered this synchrony. Furthermore, performing either choice or motor mimicry had no effect on the mimicker's affiliation towards the participant. Thus, instructed mimicry alone is insufficient to modulate cardiac coupling in minimal, structured interactions. Instead, we propose that the observed physiological synchrony reflects shared task demands and reciprocal engagement inherent in the joint task.