Summary: When people share the same physical space and feel connected, their bodies often fall into the same rhythm. A naturalistic study finds that heart rates of socially close individuals tend to rise and fall together, and that this cardiac alignment is strongest when people are near one another and paying joint attention to the same stimuli.
Researchers followed 72 students who traveled to New York City for an audio engineering competition, equipping them with a suite of wearable sensors. Data streams included continuous heart rate from wrist-worn trackers, recordings of the acoustic environment captured by hearing devices, and GPS location from mobile phones. Collecting these measures in real-world settings allowed the team to test whether physiological synchrony occurs outside controlled laboratory environments.
The analysis showed clear patterns: heart rate synchrony increased when participants were physically close—particularly within a 20-meter range—and rose further during episodes of shared attention, such as attending the same lecture or listening to the same auditory event. By contrast, noisy, chaotic sound environments weakened or eliminated synchrony, suggesting that listening conditions and environmental complexity interfere with the bodily alignment that reflects social engagement.
Key Findings
- Proximity matters: Synchrony peaked when participants were within roughly 20 meters of each other, indicating that physical closeness contributes to physiological alignment.
- Joint attention amplifies synchrony: Shared focus on the same external stimulus—listening to a lecture or the same sound source—was a strong driver of concurrent heart rate fluctuations.
- Familiarity increases baseline synchrony: Pairs or groups who already knew each other showed higher levels of alignment than strangers did.
- Noise disrupts connection: High ambient noise and poor signal-to-noise conditions reduced synchrony, often to levels similar to noninteractive settings.
- Listening effort drains cognitive capacity: In loud environments, extra effort to perceive and segregate auditory signals appears to trigger stress and consume cognitive resources, leaving less capacity for social attunement.
Source: PNAS Nexus
Overview: Hanlu He and colleagues used multimodal wearable technology to collect heart rate, GPS, and acoustic recordings from 72 students across several multi-day visits to New York City. This approach allowed the research team to align physiological measures with precise spatial and acoustic context, revealing when and where interpersonal synchrony occurs in everyday life.
Participants were considered physically close when GPS data placed them within a 20-meter radius of one another. Across trips and contexts, heart rate synchrony rose during close-proximity interactions and during moments of joint attention to the same auditory or visual stimulus. Social familiarity prior to the trip was associated with stronger and more consistent synchrony, suggesting that preexisting relationships facilitate physiological alignment.
The sound environment played a clear moderating role. Periods with moderate sound levels and relatively high signal-to-noise ratios supported greater synchrony, while environments with excessive background noise reduced synchrony. The authors propose two complementary explanations: first, noisy settings demand heavier auditory processing and compensation, which increases stress and consumes cognitive resources that would otherwise support interpersonal alignment; second, active interaction and shared attention—especially around auditory stimuli—may themselves generate synchrony, so when those interactions are impaired by noise the synchrony diminishes.
Key Questions Answered:
A: The study combined three continuous data streams: wrist-worn devices for heart rate, hearing devices that recorded ambient acoustic features, and mobile phones for GPS location. Synchronizing these streams allowed the team to match heart rate fluctuations with precise spatial positions and acoustic conditions throughout the participants’ real-world activities.
A: Joint attention places two or more people on a similar cognitive timeline: they experience the same moments of surprise, focus, or emotional response. That shared processing appears to coordinate autonomic responses, producing matched micro-changes in physiological arousal that show up as synchronized heart rate patterns.
A: Loud or chaotic acoustic environments force listeners to expend extra effort to detect and separate relevant sounds from background noise. That effort can trigger micro-stress responses and consume limited cognitive resources, leaving fewer resources available for monitoring and mirroring social partners. As a result, physiological synchrony declines in such conditions.
Editorial Notes:
- This piece was edited by a Neuroscience News editor.
- The journal paper was reviewed in full for accuracy.
- Additional contextual details were added by editorial staff.
About this social neuroscience research news
Author: Hanlu He
Source: PNAS Nexus
Contact: Hanlu He – PNAS Nexus
Image: Image credit: Neuroscience News
Original Research: Open access. “Heart rate synchrony as a marker of real-world social engagement” by Hanlu He, Jeppe H. Christensen, A. Josefine Munch Sørensen, and Ivana Konvalinka. PNAS Nexus. DOI: 10.1093/pnasnexus/pgag181
Abstract
Heart rate synchrony as a marker of real-world social engagement
Human social behavior plays out in complex, noisy real-world settings where reliable markers of engagement are hard to find. Interpersonal physiological synchrony—coordinated changes in measures such as heart rate—has been proposed as one such marker, but evidence from everyday life has been limited.
To test how social and environmental factors influence synchrony, the authors continuously recorded heart rate, GPS location, and acoustic features from 72 participants across three multiday trips to New York City. The results showed consistent increases in heart rate synchrony when people were in close proximity, demonstrating that shared physical context can elicit alignment outside the lab.
Synchrony was stronger among socially familiar peers and emerged during close-proximity interactions and joint attention to shared stimuli, but not during dispersed or noninteractive moments. The acoustic environment also modulated synchrony: low-to-moderate sound levels and favorable signal-to-noise ratios were linked to higher synchrony, whereas excessive noise reduced synchrony to levels resembling noninteractive settings.
These findings indicate that interpersonal physiological synchrony naturally arises in everyday social settings and is shaped by proximity, social familiarity, interaction context, and the surrounding soundscape—supporting its use as a marker of real-world social engagement.