Sara Fernandez Abalde^1,2, Felix Bigand¹, Trinh Nguyen¹, Roberta Bianco¹, Peter E. Keller^3,4, Giacomo Novembre¹; ¹Neuroscience of Perception and Action Lab, Italian Institute of Technology, Rome, Italy, ²The Open University Affiliated Research Center, United Kingdom, ³Center for Music in the Brain, Aarhus University, Denmark, ⁴The MARCS Institute for Brain, Behaviour and Development, Western Sydney University, Australia

Joint music making is a statistical human universal, occurring in nearly all documented human societies, suggesting an underlying predisposition for collective musical behavior. However, research in this domain has predominantly focused on trained musicians. To study interpersonal musical coordination independently of musical expertise, we used e-music boxes: digital instruments that allow participants to control the tempo of pre-registered songs through cyclic hand movements. We examined whether ancillary body movements, i.e., movements not required to produce music, facilitate interpersonal synchronization, and whether this effect depends on musical expertise. Forty dyads (20 musician pairs, 20 non-musician pairs) synchronized their musical output, either with or without visual access to each other, but never to each other’s instrumental movements. Musical output was encoded as continuous oscillatory signals, enabling precise computation of interpersonal synchrony. In parallel, we recorded full-body kinematics, and electroencephalography from both participants simultaneously. Results showed that seeing the partner significantly improved interpersonal musical synchronization, irrespective of musical training. Using principal component analysis, we separated instrumental from ancillary movements in the kinematic data. While all movements exhibited periodicities aligned with the musical bar, ancillary movements additionally showed a faster periodicity aligned with the musical beat (i.e., the basic temporal pulse of the music). This beat-related periodicity was enhanced when partners were visible, particularly in upper-body anteroposterior sway and head bobbing. Moreover, visual access increased interpersonal synchronization across several ancillary movements, including upper body sway, head movements and lateral sway, specifically at beat-aligned frequencies, but not at bar-aligned frequencies. A mediation analysis showed that interpersonal synchronization of ancillary movements mediated the effect of vision on musical synchronization. This indicates that visual information extracted from a partner’s body movements provides coordination-relevant cues for joint action, independently of musical training. Ongoing electroencephalography analyses aim to identify the neural mechanisms underlying this visual–sensorimotor coupling.