OSMoSIS: A novel tool for assessing social motor synchrony in autistic children

This paper introduces OSMoSIS, a novel tool for assessing Social Motor Synchrony (SMS) in naturalistic child-facilitator interactions. Unlike Motion Energy Analysis (MEA), which is limited to seated or highly controlled tasks, OSMoSIS captures full-body interactions and computes synchrony through position correlation (PC) and specific kinetic energy correlation (SKEC). We evaluated OSMoSIS during music therapy sessions with twelve autistic children, using synchronous (movement-contingent) and asynchronous (non-contingent) sound mappings as a testbed to elicit contrasting interaction dynamics. Our results show that SKEC was sensitive to condition differences, whereas PC was not in this setting, indicating that OSMoSIS provides a suite of indices in which SKEC serves as the primary marker for dynamic, whole-body contexts and PC as a supporting, posture-aligned measure. Complementary coding with Interact behavioural coding software revealed reduced non-response under synchronous conditions, supporting the convergent validity of OSMoSIS. We argue that OSMoSIS advances the measurement of SMS beyond MEA, enabling analysis in ecologically valid contexts such as therapeutic and educational interventions.