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Perceiving someone’s heartbeat can be a powerful experience. One would normally perceive only one’s own heartbeat or the heartbeat of someone (physically) very close, by putting one’s ear the other person’s chest. This is clearly an intimate experience. Also, heartbeats are used in different media. For instance, in movies, playing the sound of the heartbeat of a character can enhance the excitement or tension in the movie. Similar effects are sometimes used in games by giving, for instance, haptic feedback through a game controller at the rhythm of a heartbeat (e.g., in Metal Gear Solid). Furthermore, Werner, Wettach, and Hornecker (2008) and Janssen, Bailenson, Ijsselsteijn, and Westerink (2010) showed that feeling someone else’s heartbeat can be a very intimate experience. This suggests that perceiving someone else’s heartbeat can create strong social experiences.
Perceiving another person’s heartbeats might create a strong social experience because heartbeats are strongly related to emotions (Kreibig, 2010), and emotions are an important component of many social interactions (e.g., Frijda & Mesquita, 1994; Keltner & Haidt, 1999; Keltner & Kring, 1998). To give a few examples, emotional displays promote trust and reconciliation (Keltner, 1995), facilitate attachment (Bowlby, 1969), and elicit social contact (Schachter, 1959). Emotions also help to create common ground in social interactions by eliciting expressed emotions in a perceiver of those emotions (Hatfield, Cacioppo, & Rapson, 1994; Shortt & Pennebaker, 1992). Furthermore, emotions have the property that they elicit the sharing of emotions (Rime, 2009). Hence, emotions propagate through social networks (Rime, Philippot, Boca, & Mesquita, 1992), which can be useful for, for instance, obtaining help, support, or advice, arousing empathy, gaining attention, receiving comfort, or letting off steam (Rime, 2007). Hence, emotions are at the core of many social and intimate interactions.
The relation between emotion and heart rate (HR) and heart rate variability (HRV) has been widely investigated. In fact, HR is the most often adopted physiological measure of emotion (Kreibig, 2010). After a review of 134 studies, Kreibig (2010) concluded that HR increases with both negative and positive emotions (e.g., Hess, Kappas, McHugo, Lanzetta, & Kleck, 1992; Adsett, Schottstaedt, & Wolf, 1962; Khalfa, Roy, Rainville, Dalla Bella, & Peretz, 2008; Gehricke & Fridlund, 2002; Boiten, 1996; Tugade & Fredrickson, 2004; Robin, Alaoui-Ismaili, Dittmar, & Vernet-Maury, 1998; Murakami & Ohira, 2007). This can be explained by the fact that emotions trigger a behavioral reaction (sometimes called a fight-or-flight response; Cannon, 1927), which requires increased blood flow to the muscles. A few exceptions included emotions comprising an element of passivity (e.g., contentment, non-crying sadness, affection), which may result in decreases in HR (e.g., Christie & Friedman, 2004; Hess et al., 1992; Nyklicek, Thayer, & Van Doornen, 1997) as they do not trigger a behavioral reaction.