When interacting with someone who shares a similar age or racial background, people tend to naturally coordinate their body movements more smoothly than when speaking with someone from a different background. These physical rhythms often happen without people realizing it, suggesting that shared visible traits provide a foundation for smoother interpersonal connections. This research was recently published in the Personality and Social Psychology Bulletin.
Spontaneous behavioral synchrony refers to the way people unconsciously coordinate their actions, movements, and pacing during a conversation. This phenomenon involves moving at the same time, matching the speed of actions, and blending gestures together smoothly. It looks a bit like a subtle, unchoreographed dance between two conversation partners.
In psychological research, this physical mirroring typically signals rapport, which is the feeling of interpersonal chemistry and closeness between individuals. When two people click, their bodies often reflect that connection by moving in harmony. Scientists wanted to understand what specific factors predict whether this physical coordination will emerge naturally between strangers.
“Much of the existing research asks what happens after people become behaviorally synchronized, for example, whether it leads to greater trust, stronger relationships, or better teamwork,” said Morgan D. Stosic, a research psychologist with KBR at NASA’s Johnson Space Center. Stosic, who earned her doctorate in psychology from the University of Maine in 2023, conducted the study independently of her work at NASA. “Much less attention has been given to a more fundamental question: What causes people to become synchronized in the first place?”
Past theories suggest that individuals who perceive themselves as similar to one another might feel more relaxed and experience greater chemistry. Specifically, highly visible characteristics like age and race are some of the first traits people use to gauge similarity. Sharing these traits might reduce initial anxiety and free up mental energy, making it easier for people to focus on their partner and fall into a shared physical rhythm.
“Our goal was to understand whether sharing visible characteristics with another person, specifically age and race, influences how naturally people connect,” Stosic said. “We wanted to better understand whether these shared characteristics shape our social interactions from the very first meeting.”
To test this idea, researchers set up interactions between people who either shared or did not share the same race or age category. The team evaluated three separate studies featuring female participants who interacted in pairs, known as dyads. The authors focused strictly on women to keep gender constant, as women generally show higher rates of spontaneous behavioral coordination than men.
In the first study, 182 university students formed 91 pairs of strangers. These participants completed a collaborative problem-solving task over a video conferencing platform. Some of the pairs shared the same racial background, while others did not.
“We looked at two outcomes: behavioral synchrony, which is the subtle tendency for people’s movements and behaviors to become coordinated in time, and how close and connected people reported feeling after meeting,” Stosic told PsyPost. “To study this, we paired strangers who were either similar or different in age and race and observed how they interacted.”
The scientists recorded the interactions and extracted three separate one-minute video clips from the beginning, middle, and end of the conversations. Trained human coders watched these silent clips and rated the pairs on their simultaneous movements, tempo similarity, and overall smoothness. The researchers also analyzed the same video clips using an automated software program that tracks human body joints to measure simultaneous movement.
After the video task, the participants filled out surveys rating how much rapport they felt with their partner. The authors found that pairs sharing the same race synchronized their behaviors significantly more than pairs from different racial backgrounds. This difference in movement coordination was only detected by the human coders.
The automated software did not register a difference based on race. The computer scores also failed to correlate with the participants’ own ratings of rapport, indicating the software might not be capturing the true essence of interpersonal chemistry. Interestingly, even though the same-race pairs moved more in sync, the participants themselves did not report feeling any difference in rapport compared to the mixed-race pairs.
“One of the most interesting findings was that people didn’t report feeling any closer to someone simply because they were the same age or race,” Stosic said. “However, trained observers rated people who were similar in age and race as moving and interacting in more synchronized ways. This suggests that subtle aspects of our behavior can reflect shared characteristics, even when our conscious or explicitly reported feelings do not.”
The second study moved the interactions into a face-to-face laboratory setting to see if the findings would hold up in person. This study included 88 women who formed 44 pairs, drawing from a pool of younger adults aged 18 to 24 and older adults aged 60 to 90. The pairs sat side-by-side and spent 15 minutes planning a pretend vacation together using a world map and fake money.
Once again, the researchers categorized the pairs based on whether they matched in race or age. They used human coders and the automated software to evaluate short video clips of the interactions, and they collected self-reported rapport surveys. In this smaller sample, the scientists did not find any statistically significant differences in physical coordination or self-reported rapport based on race or age similarities.
To get a better understanding with a larger group, the authors conducted a third study that replicated the face-to-face vacation planning task of the second study. This final group included 182 women making up 91 pairs. They performed the exact same task but for 10 minutes instead of 15.
In this third study, the results showed that same-age pairs synchronized their behaviors significantly more than mixed-age pairs. Just like in the first study, this physical coordination was picked up by human coders rather than the computer software. The effect of racial similarity on physical coordination was not statistically significant in this specific group.
To make sense of the varying results across the three experiments, the researchers pooled all the data together into a combined analysis involving 450 total individuals. By combining the data, they gained enough statistical power to spot broader trends. The combined analysis showed that pairs sharing the same age and pairs sharing the same race both demonstrated significantly higher levels of behavioral synchrony than pairs with mixed backgrounds.
This combined analysis also confirmed that human observers were much better at detecting this coordination than the computer software. The human ratings consistently matched up with the psychological concept of rapport, which provides evidence that the coders were measuring a meaningful social behavior. The automated software failed to relate to rapport at all across the entire dataset.
“One of the biggest surprises was that the computer vision method we tested didn’t perform as well as we expected,” Stosic said. “Traditionally, behavioral synchrony has been measured by trained human observers, but researchers are increasingly turning to computer vision because it can analyze interactions much more quickly.”
The automated tool used in this study only tracked the simultaneous movement of joints, missing the more nuanced aspects of shared tempo and overall smoothness that human observers can perceive. The software might also have struggled to map movements accurately because the videos only showed participants from the waist up.
“In our study, however, the automated approach didn’t accurately capture synchrony in the way we had expected,” Stosic said. “That could have been due to factors like video quality, lighting, or limitations of the software itself. Whatever the reason, it was an important reminder that newer technologies aren’t automatically better, they need to be carefully validated before researchers rely on them to measure complex human behavior.”
Another complex finding is the gap between how the participants behaved and what they reported on their surveys. The combined data confirmed that age and racial similarities had absolutely no impact on how much chemistry the participants claimed to feel on their surveys.
“One important caveat is that people’s self-reported feelings didn’t always match their observable behavior,” Stosic said. “Participants reported feeling similarly close to their partners regardless of age or race, yet trained observers saw greater behavioral synchrony among people who were more similar.”
Stosic noted that this discrepancy does not necessarily mean that either measure is wrong. “Instead, it suggests that human connection is complex,” she said. “How close we feel to someone and how we behave around them may capture different aspects of social interaction.”
People in mixed-race or mixed-age pairs might have intentionally adjusted their survey responses to avoid looking prejudiced. Alternatively, rapport is made up of multiple components, including mutual attention and positivity. People in mixed groups might have compensated for a lack of physical rhythm by smiling more or paying closer attention to their partners.
“While it’s possible that self-reports don’t always perfectly reflect people’s true feelings, it’s equally possible that behavioral synchrony is just one piece of what makes us feel connected to another person,” Stosic said.
One limitation to consider is that the human coders might have harbored unconscious biases, seeing more harmony in pairs who looked similar to one another. To test this, future research could use video filters that obscure the physical identities of the participants, leaving only their outlines visible to the coders. Additionally, the exclusive use of female participants means these findings might not apply to men or mixed-gender groups.
“That’s the direction we’d like to see this research go,” Stosic said. “While our study focused on age and race, there are many other characteristics, both physical and psychological, that may influence whether people naturally ‘click.’ By better understanding what fosters these subtle social connections, we can gain deeper insight into how successful relationships and effective teams develop, whether in everyday life, the workplace, or even high-stakes environments like healthcare and spaceflight.”
The study, “A Multimethod Assessment of Spontaneous Behavioral Synchrony in Race- and Age-Concordant Versus Discordant Dyads,” was authored by Morgan D. Stosic, Adele E. Weaver, Ken Fujiwara, Ishabel M. Vicaria, Derek M. Isaacowitz, and Mollie A. Ruben.
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