Cardiac synchrony during collaborative drawing: A longitudinal comparison of same generation and intergenerational dyads

This longitudinal study of collaborative drawing programs found that while interpersonal distance and self-reported closeness effectively characterized relationship development in both intergenerational and same-generation dyads, cardiac synchrony showed only a marginal link to active collaboration specifically within intergenerational pairs.

The Gist

The Big Picture: A Six-Week Art Class Experiment

Imagine a community center where strangers are paired up for a six-week art class. The goal is to see if doing creative things together helps people bond, and if we can "see" that bonding happening inside their bodies.

The researchers set up two types of pairs:

1. The "Mix-and-Match" Pairs: An older adult (grandparent age) paired with a younger adult (college age).
2. The "Same-Gen" Pairs: Two younger adults paired together.

For six weeks, these pairs met up. They didn't just chat; they had to draw pictures together on the same piece of paper without talking, and they also did other team tasks like solving a puzzle. While they worked, the researchers strapped them with special sensors to track two things:

• How close they sat to each other (measured by cameras).
• Their heartbeats (measured by sensors that look at blood flow in the brain).

The big question was: As these strangers became friends, did their hearts start beating in sync?

The Heartbeat Mystery: The "Dance Floor" Analogy

Scientists often look at cardiac synchrony (heartbeats matching up) as a sign that two people are "in the zone" together. Think of it like a dance floor. If two people are dancing perfectly together, their movements are synchronized. If their hearts are synchronized, it suggests they are sharing the same emotional energy or excitement.

The researchers hoped to find that as the pairs got to know each other, their hearts would start "dancing" together more and more.

What they found was a bit of a bummer for the "heartbeat detector" idea:

• No Magic Sync: Surprisingly, the hearts of the real pairs didn't beat in sync any more than the hearts of two random strangers who happened to be in the same room at the same time but weren't interacting.
• The "Pseudo" Pairs: The researchers even created "fake" pairs (mixing data from Person A with Person B who never met). The "fake" pairs had just as much heart-synchrony as the "real" pairs.
• The Takeaway: It seems that just sitting in a room and drawing doesn't make your heart sync up with someone else's, even if you are becoming friends. The heartbeat didn't act like a "friendship meter."

The Real Story: The "Personal Bubble" Analogy

If the heartbeats didn't tell the story, what did? The researchers found that how close people sat to each other was the real hero of the story.

Think of personal space as a bubble.

• For the Young-Young Pairs: As they got more comfortable and felt closer emotionally, they actually sat further apart. It's like when you get really comfortable with a friend; you don't need to be glued to them to feel the connection. You relax your bubble.
• For the Old-Young Pairs: This group was different. As they started to feel a connection, they sat closer together. It's like two people who are a bit nervous or unsure of each other leaning in to bridge the gap. They were trying harder to connect, so they physically closed the distance.

The Verdict: The distance between people (interpersonal distance) was a much better indicator of how their relationship was developing than their heartbeats were.

The "High Stakes" Exception

There was one tiny, interesting spark. For the Old-Young pairs, there was a slight trend where their hearts matched up a bit more when they were drawing really well together.

The researchers think this might be because the older and younger adults felt a bit more "pressure" or "stakes" in the collaboration. Maybe they were trying harder to overcome the generation gap, or maybe the task felt more important to them. When the stakes feel higher, the body reacts, and the hearts might sync up a little bit. But for the younger pairs, who felt more natural and relaxed, this didn't happen.

The Final Lesson

This study teaches us three main things:

1. Don't rely on heartbeats to measure friendship: Just because two people are in the same room doing a task doesn't mean their hearts will beat together. It's not a reliable "friendship detector" in low-stress, everyday situations.
2. Watch the distance, not the pulse: If you want to know if two people are getting along, look at how close they sit. If they are strangers, they might sit far apart. If they are getting comfortable, they might move closer (or further apart, depending on the group!).
3. Intergenerational magic is real (but complicated): When older and younger people work together, they show unique behaviors. They might sit closer and try harder to connect, which creates a unique kind of energy that is different from two people of the same age hanging out.

In short: Building a relationship is less about your heart syncing up like a metronome, and more about how you navigate the space between you. Sometimes you lean in, sometimes you lean back, but that physical dance tells a much clearer story than your heartbeat does.

Technical Summary

1. Problem Statement

Intergenerational arts programs are increasingly used to foster social connection and improve well-being, yet the physiological mechanisms underpinning relationship formation in these settings remain poorly understood. While behavioral and qualitative data suggest benefits, there is a lack of longitudinal evidence tracking how repeated social encounters shape dyadic physiological responses. Specifically, it is unclear whether cardiac synchrony (the temporal alignment of heart rate fluctuations) serves as a reliable biomarker for:

• Relationship development over time.
• Differences between intergenerational (older/younger adult) and same-generation (younger/younger adult) dyads.
• The transition from stranger to acquaintance in collaborative, open-ended tasks.

The study addresses the gap in understanding how shared arousal (indexed by cardiac synchrony) evolves across repeated encounters and whether it correlates with behavioral collaboration, self-reported social closeness, and interpersonal distance.

2. Methodology

Study Design & Participants

• Design: A longitudinal study spanning six weekly sessions.
• Participants: 122 community-dwelling participants from Zurich, Switzerland.
  • Intergenerational Dyads ($n=31$): One older adult (mean age 76) and one younger adult (mean age 24).
  • Same-Generation Dyads ($n=30$): Two younger adults (mean age 22.5).
  • All dyads started as strangers.
• Procedure: Each session involved:
  1. Self-report measures (loneliness, empathy, attitudes).
  2. Drawing Tasks: Participants drew alone once and collaboratively twice (5 minutes each) using oil pastels. Crucially, they were instructed not to talk during drawing to isolate non-verbal collaboration.
  3. Collaborative Activity: A weekly task (e.g., jigsaw puzzle in Session 3, sorting, verbal fluency).
  4. Post-Task Measures: Inclusion of Other in Self (IOS) scale.

Data Acquisition

• Physiological Signals: Cardiac signals were derived from functional near-infrared spectroscopy (fNIRS) data. Instead of standard ECG, the researchers extracted Inter-Beat Intervals (IBI) from hemodynamic signals (HbO concentration) in the bilateral inferior frontal gyri (IFG) and temporo-parietal junction (TPJ).
  • Signal Processing: HbO signals were upsampled to 100 Hz, band-pass filtered (0.5–2.5 Hz), smoothed, and peaks were identified using the AMPD algorithm to generate IBI time series.
• Behavioral Tracking:
  • Motion Capture: GoPro cameras tracked head and hand movements. OpenPose was used to estimate 2D pose coordinates to calculate Interpersonal Distance (neck joint distance).
  • Drawing Analysis: 103 external raters (via Prolific) scored drawings on "harmony" and "use of space" to generate a Drawing Collaboration score (0–200).
  • Puzzle Performance: Number of pieces assembled in a 6-minute jigsaw task.

Statistical Analysis

• Approach: Bayesian multilevel regression using the brms package in R.
• Metrics: 95% Highest Posterior Density (HPD) intervals were used to determine substantial effects (HPD does not contain zero) or trends (HPD tail overlaps zero).
• Synchrony Calculation: Cross-correlation functions (CCFs) were computed between dyad members' IBI time series across lags of ±3 seconds.
• Control: Comparisons were made between "real" dyads and "pseudo" dyads (randomly paired participants) to distinguish true interaction effects from environmental or homeostatic rhythms.

3. Key Contributions

1. Longitudinal Physiological Tracking: One of the first studies to track cardiac synchrony longitudinally across six sessions in an intergenerational context, moving beyond single-session "first encounter" studies.
2. fNIRS-Derived Cardiac Synchrony: Demonstrated the feasibility and limitations of extracting cardiac IBI signals from fNIRS data in a collaborative setting, offering a method to simultaneously measure neural and cardiac dynamics.
3. Objective Measure of Proximity: Validated interpersonal distance (neck-to-neck distance) as a promising, objective behavioral marker for relationship development, showing distinct patterns between intergenerational and same-generation dyads.
4. Critical Evaluation of Cardiac Synchrony: Provided robust evidence challenging the utility of cardiac synchrony as a standalone biomarker for social connection in low-stakes, open-ended collaboration.

4. Results

Behavioral and Self-Report Measures

• Drawing Collaboration: Intergenerational dyads showed significantly higher collaboration scores than same-generation dyads.
• Puzzle Collaboration: Same-generation dyads performed significantly better (faster/more pieces) than intergenerational dyads.
• Social Closeness: Intergenerational dyads reported higher cumulative social closeness but also greater discrepancy in closeness feelings between partners compared to same-generation dyads.
• Interpersonal Distance:
  • Intergenerational dyads sat closer together when they felt socially closer (positive correlation).
  • Same-generation dyads sat closer when they felt less socially close or had larger discrepancies in closeness (negative correlation), suggesting a compensatory behavior for discomfort.

Cardiac Synchrony Findings

• Real vs. Pseudo Dyads: There was no substantial difference in cardiac synchrony levels between real dyads and pseudo dyads (randomly paired strangers) across all sessions or tasks. This suggests the observed synchrony was likely driven by shared environmental demands rather than true dyadic interaction.
• Group and Task Effects: No substantial differences were found in cardiac synchrony based on generation (inter- vs. same), task type (drawing alone vs. together), or session number.
• Correlations with Behavior:
  • Generally, cardiac synchrony did not covary with drawing collaboration, puzzle performance, social closeness, or interpersonal distance.
  • Exception (Trend): A trending positive relationship was observed between drawing collaboration and cardiac synchrony only for intergenerational dyads (across 21 of 25 time lags). This suggests that in high-stakes or high-tension intergenerational collaboration, shared arousal may increase, but the effect was not statistically "substantial" by the study's strict Bayesian criteria.

5. Significance and Implications

• Limitations of Cardiac Synchrony as a Biomarker: The study concludes that cardiac synchrony is not an optimal measure for predicting collaborative outcomes or relationship development in everyday, low-stakes community settings. The lack of differentiation between real and pseudo dyads implies that shared environmental context (e.g., the drawing task itself) drives physiological alignment more than the social relationship.
• Context Matters: The trending relationship in intergenerational dyads suggests that cardiac synchrony might only emerge under conditions of "higher stakes" or increased social tension (e.g., navigating age gaps, managing uncertainty), rather than in smooth, established collaborations.
• Interpersonal Distance as a Proxy: The study highlights interpersonal distance as a more reliable, objective, and sensitive measure of relationship development than cardiac synchrony in these contexts. The opposing patterns of distance vs. closeness between the two groups reveal complex social dynamics where physical proximity may compensate for social discomfort.
• Policy and Practice: For organizations implementing intergenerational programs, the findings suggest that relying on wearable physiological monitoring (like heart rate) to measure program success may yield low explanatory power. Instead, behavioral metrics (like proximity and collaborative output) and self-reports offer more robust insights into relationship formation.

In summary, while intergenerational programs foster social connection, the physiological mechanism of "shared arousal" via cardiac synchrony appears less sensitive to relationship quality than previously hypothesized, particularly in open-ended, non-threatening collaborative tasks.