Real-World Study Finds Heart-Rate Synchrony Linked to Proximity, Familiarity and Sound Levels

Researchers led by Hanlu He at the Technical University of Denmark examined interpersonal physiological synchrony outside the laboratory. The sample comprised 72 university students (19-32 years old, 60 men) who entered the Oticon-sponsored Audio Explorer Challenge in pre-formed teams of 2-5 members. Winning teams earned three separate four-day trips to New York City (23, 24 and 25 participants per trip). During each day (09:00-22:00) participants wore wristbands that recorded heart rates, hearing-aid-style devices that logged ambient sound every 20 seconds, and smartphones that captured GPS locations. Social familiarity was defined by team membership; dyads from the same team were “familiar,” others “unfamiliar.” Continuous data allowed researchers to assess heart-rate fluctuations relative to physical proximity, shared attention (e.g., watching a lecture) and sound-environment characteristics.

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Across all trips, heart-rate patterns tended to align when participants were physically close. Synchrony was strongest among familiar peers and during low-to-moderate sound levels with clear signal-to-noise ratios. In very noisy settings, synchrony declined. The authors interpreted these patterns as evidence that shared environmental context can elicit physiological coupling, especially when individuals attend to the same stimulus.

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The study suggests that interpersonal physiological synchrony can serve as a marker of real-world social engagement, reflecting how proximity, social ties, and auditory conditions shape collective bodily responses. Because synchrony has been linked in prior work to empathy, rapport and cooperation, the findings may inform fields ranging from social neuroscience to design of collaborative spaces.

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The authors acknowledge that the data cannot disentangle whether proximity itself or the concurrent activities drive synchrony. Likewise, it is unclear whether sound-environment effects stem from acoustic properties or from the typical activities performed in those settings. These gaps limit causal inference and highlight the need for more granular interaction coding in future research.

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• “These findings demonstrate that interpersonal physiological synchrony emerges in naturalistic social settings and is modulated by physical proximity, social familiarity, social context, and the sound environment, establishing it as a reliable marker of real-world social engagement,” — study authors

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• “It therefore remains unknown whether it was physical proximity itself or the similar activities participants were performing that drove interpersonal physiological synchrony.” — study authors

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• “It also remains unknown whether the differences in synchrony found in different sound environments were driven by the sound environments themselves or by the types of activities that are typically performed in different sound environments.” — study authors

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• “Heart rate synchronization also depended on the sound environment.” — study authors

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