Subconscious Physiological Responses Predict Attraction

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It is very difficult to predict whether two people will be attracted to one another, especially when they meet for the first time. Fascinating research by Prochazkova and colleagues, published in November 2021 in the journal Nature Human Behaviour, reveals that a couple’s subconscious physiological responses to one another may predict their mutual attraction. The researchers found that when individuals feel mutual attraction, their physiological arousal responses (such as heart rate) also match one another. This research further suggests that our subconscious physiological responses are stronger predictors of attraction than our consciously controlled responses (such as smiling and eye gaze). Subconscious physiological synchrony may be an indicator that couples “click” with one another or feel a “spark."

Lead researcher Prochazkova and colleagues from the Netherlands and the UK investigated heterosexual men and women’s physiological and self-reported responses to meeting a blind date for the first time. The researchers set up a mobile first-date cabin which they brought to festivals throughout the Netherlands. They recruited 70 women and 70 men who were single and between ages 18 and 38 to participate in a “blind date” study. Individuals were randomly assigned to a partner of the other sex and could not see one another until the researchers dropped the divider between them. Participants wore eye-tracking glasses as well as electrodes measuring heart rate and skin conductance. Participants first indicated how attractive they thought their partner was and then engaged in both a 2-minute verbal and a 2-minute nonverbal interaction. (Some participants had the verbal interaction first while others had the nonverbal interaction first.) Pairs rated their attraction to one another again and reported whether they wanted to go on a second date with their partner.

Consistent with prior research, men were more attracted to women than vice versa (53% of men and 34% of women wanted to go on a second date with their partners); however, only 17% of couples mutually desired a second date. (Couples that mutually desired a second date were provided with each other’s contact information one week later.) The researchers found that smiling, laughing, and eye contact (all controllable and conscious physiological responses) did not predict dyads’ liking for one another. However, couples that were attracted to one another tended to match one another in levels of heart rate and skin conductance—relatively uncontrollable and unconscious physiological responses. The authors concluded that unacquainted individuals whose heart rate and skin conductance (measures of arousal) increase and decrease in synchrony also felt more strongly attracted toward each other.

Over the course of the interaction, some pairs became more attracted to one another while others became less attracted. Couples did tend to reciprocate one another’s smiles, laughs, head nods, and eye contact; however, reciprocating these conscious physical responses did not predict romantic attraction among those couples. Interestingly, couples’ mutual attraction was significantly predicted by their unconscious and unintentional physiological response synchrony. The authors state: "Specifically, the more couples’ SC [skin conductance] and their HR [heart rate] synchronized, the more attracted participants were to their partner.” The authors also found that synchronized physiological responses in both verbal and nonverbal interactions were associated with increased attraction. The authors stress that attraction was not predicted by individuals’ physiological responses alone, rather, it was predicted by the matching in physiological arousal responses of both members of the couple. The authors suggest that “these results highlight the importance of subconscious physiological coupling in the development of romantic attraction.” They also note that because matching of physiological responses involves both partners’ nervous systems adjusting in response to a partner’s physiology, and that this type of response would be difficult or impossible to purposefully regulate, this matching in physiological arousal is the result of “genuine emotional exchange.”

The authors acknowledge that, presently, the direction of the relationship between physiological arousal synchrony and attraction is unclear. It is possible that when couples’ physiological responses match, synchrony causes increased liking, or it is possible that increased liking causes couples’ physiological responses to synchronize. The authors also acknowledge that this sample was limited to heterosexual Dutch couples and recommend studying same-sex couples in the future.

As the researchers' review, in established couples, physiological synchrony is associated with romantic satisfaction as well as the ability to accurately identify a partner’s emotional state. Physiological responses are also more likely to be matched when couples share intimate moments such as eye gazing or touching. Researchers have speculated that matching in physiological responses might facilitate deeper emotional understanding in couples.