Researchers at Leiden University and Utrecht University found that synchronized bodily responses do not always mean people are cooperating. The study, published in Proceedings of the Royal Society B: Biological Sciences, used 122 participants to test this link. Results showed that matching skin conductance does not guarantee greater human reciprocity.
Sometimes, while people are interacting with each other, their movements and physiological responses can fall into step. Some past studies have linked synchronized bodily responses to cooperation and being attuned to the emotions of others.
A common way of detecting physiological synchrony entails measuring people's skin conductance, or in other words, how easily small electrical currents pass through the skin. This measure reflects the activity of sweat glands, which can become more active when people are more aroused, physically active or stressed.
Researchers at Leiden University and Utrecht University recently set out to further explore the link between skin conductance synchronization during face-to-face interactions and cooperation. The results of their experiments, published in Proceedings of the Royal Society B: Biological Sciences, suggest that matching bodily responses are not always associated with greater reciprocity (i.e., giving something back in response to receiving something) and cooperation.
"Physiological synchrony is a very fascinating phenomenon: when we interact with somebody, our physiologies (such as our heart rate or our pupil size) somehow start to move in sync," Fabiola Diana, first author of the paper, told Phys.org. "The mechanism behind this is still unknown, but this happens all the time—between mothers and their children, between romantic or friend couples, between therapist and patient."
Some past research focusing on physiological synchrony suggested that greater synchrony is associated with people feeling more "connected" or attuned to each other. This could in turn promote trust, reciprocity and cooperation.
"Since trust is the very backbone of human society, and many daily life situations require us to put our trust in complete strangers (e.g., asking someone to look at your purse while you are going to the bathroom), our primary objective was to research whether this synchrony could also be one of the reasons why people who do not know each other trust one another," said Diana. "Another thing we were interested in is how people synchronize. How does it happen? Is there maybe something in the faces of people that makes us synchronize more?"
People's synchronization during face-to-face interactions
To dive deeper into the link between synchrony and cooperation, Diana and her colleagues recruited 122 participants and ran a simple experiment. The participants were paired up with complete strangers and fitted with several electrodes to measure their physiological signals.
The electrodes they used could monitor the participants' heart rate and their skin's electrical conductance. Throughout the experiment, the team also recorded the participants' facial expressions using cameras. In some experimental trials, pairs of participants could see each other, while in others they could not.
"We then asked them to play the so-called 'trust game,' a very simple laboratory version of everyday trust: one person takes a risk by giving something valuable to another person, who then decides alone whether to repay that trust," explained Diana.
"Because the trustor never learns what the other person did during the game, they must act without reassurance, control or the chance to adjust. It is like lending €10 to a stranger and then walking away without ever seeing whether they give any of it back. You have made yourself vulnerable; they alone decide what happens next."
The game that the participants played was designed to create a clear power imbalance. By trusting the person they were playing with, participants made themselves vulnerable and gave up control, while the other person gained greater control over the game's outcome. During the game, the person making the initial contribution is dubbed the trustor, while the person deciding whether to give something back is called the trustee.
"The two roles place people in very different affective states: the trustor may feel more uncertain, exposed or anxious, whereas the trustee may feel more powerful and in control," said Diana. "This difference is important."
When they analyzed the physiological responses, game outcomes and video recordings they collected, the researchers found that the skin conductance responses of paired participants were more synchronized when they could see each other. Notably, differences in facial expressivity, or how expressive participants' faces were, did not appear to account for the greater synchrony during face-to-face interactions.
"For years, we have assumed that synchrony is a social superpower: when we move, breathe or respond in time with someone else, we feel closer to them, and we become more cooperative, generous and willing to give back," said Diana. "Our findings suggest a more complicated story. Synchrony may work less like a 'connection button' and more like an emotional amplifier: it can make us feel what the other person feels. And that is not always a good thing."
The team found that greater skin conductance synchrony was associated with reduced reciprocity, but only when partners could see each other. Exploratory analyses also suggested that this relationship depended on participants' level of arousal (i.e., bodily activation).
"Crucially, this effect showed up in participants' bodily responses," said Diana. "Their bodies seemed to register the shared state of the interaction, and this bodily resonance helped explain why they later behaved less reciprocally. In short: it is not simply whether we synchronize that matters, but what we synchronize on."
Guiding future research focusing on body synchronization
The results of this study challenge the assumption that physiological synchrony consistently supports cooperation and reciprocity. Instead, they suggest that the relationship between synchrony and cooperation depends on the circumstances of an interaction and participants' bodily activation.
"If synchrony is not simply a force for connection, but a way of bodily tuning into another person, then it may also be one of the tools we use to understand them," said Diana. "My next question is whether synchrony helps us predict what others will do next."
The recent work by Diana and her colleagues could inspire other research groups to explore the link between synchronized bodily responses and cooperation. As part of her next studies, Diana hopes to also assess whether synchrony helps people anticipate another person's next actions during in-person interactions.
"When we fall into rhythm with someone, we may pick up subtle information about their intentions, emotions and likely actions, sometimes before they say or do anything explicit," added Diana. "In other words, synchrony could be part of what makes humans good social predictors. It may allow us to anticipate whether someone is about to cooperate, withdraw, become aggressive or offer support.
"So, in my future research I would like to investigate the possibility that synchrony is not just something that happens between people; it may be a bodily mechanism through which we read, understand and anticipate one another."