Touch is the simplest and most direct of all sensory systems 1. It has been described as the paramount mean of interpersonal exchange, which plays a crucial role in emotional processing, social interactions, and cognition (Gallace & Spence, 2010). The skin has been defined “a social organ” 4 and whether touch comes from a firm handshake, an encouraging pat on the shoulder, or a gentle caress, it has a strong and direct nonverbal communicative function 5. The pleasant effects of social touch are mainly determined by a particular type of touch called affective touch; a touch resembling a caress, essential for emotions’ communication and social bonds 5. The affective touch is a standalone type of tactile experience that relies on an the hyper-specialized somatosensory system, called CT-afferent system, which is activated by slow and gentle strokes (McGlone et al., 2007; McGlone et al., 2012) and a temperature close to the one of the human skin 8. However, differently from the unequivocal nature of discriminative touch, affective touch can have a positive or a negative valence depending on several factors, such as speed and the body’s area in which the touch occurs (Gallace & Spence, 2010; McGlone et al., 2014), socio-cultural norms, context, gender 10, interpersonal relationships, identity of the person providing the touch (Lee & Guerrero, 2001; Ellingsen et al., 2016; Morrison et al., 2010), and nonverbal visual cues 13.
Research conducted across the last few decades has come to the agreement that the pleasant effects produced by affective touch vary as a function of the relationship between individuals. Undoubtedly, more frequent physical contact and closeness are observed among romantic partners than strangers. Being touched by one's partner lowers arousal levels by reducing the activity of brain areas involved in alarm processing (Coan et al., 2006; Triscoli et al., 2017), promotes recovery following a stressful event 16, diminishes pain perception, and prompts physiological coupling between partners 17. On the contrary, being touched by a stranger does not produce the calming and analgesic effects observed between partners and it can rather induce states of anxiety and discomfort (Goldstein et al., 2017; Ellingsen et al., 2016). Indeed, an unexpected touch from a stranger is likely to be experienced as discomforting and unpleasant (Sussman & Rosenfeld, 1978).
Another relevant aspect reported to modulate the hedonic experience of affective touch is the gender of the subjects involved in the social interaction. Russo and colleagues (2020) have reported a gender asymmetry in the evaluation of affective touch with females showing higher sensitivity, pleasantness, and accuracy in communicating feelings and emotions via touch than men. For example, women respond more negatively than men when touched by a different-gender stranger 22. Females also tend to find less pleasant a touch from a male stranger than a male friend, while men are equally comfortable with a touch from either a woman stranger or a woman friend 23. Nonetheless, studies on the modulatory effect of gender on affective touch are dated 24, often inconsistent 25 and mainly based on participants’ subjective rating.
Recent studies have also pointed out the possible contribution of visual cues as a factor that might come into play during affective touch (Ellingsen et al., 2016; Sailer & Leknes, 2022). Among several social cues, eye contact has been considered a rich source of social information that promotes social interactions in both human 27 and non-human primates 28. Eye contact has been argued to play a leading role in strengthening emotional sharing between individuals and evoking positive affective reactions 29. Nevertheless, the meaning of eye contact is subordinated to contextual factors and to interpersonal relationships (Emery, 2000; Dal Monte et al., 2016); an eye contact with a familiar person, but not with a stranger, can enhance affection, attention, and social inclusion 32. Although eye contact is a key feature of social interaction and in daily life often affective touch occurs together with eye contact exchange, only a few studies have assessed the link between eye gaze and touch (Meier et al., 2020; Kerr et al., 2019), and their relationship still remains largely understudied.
However, previous research focusing on the influence of interpersonal relationship, gender, and eye contact only considered the person receiving an affective touch; how these factors drive the hedonic and autonomic responses on the person promoting an affective touch has been largely neglected.
To fill in this gap, with a series of experiments we investigated the hedonic and physiological responses on the person promoting an affective touch. In Experiment 1, we examined whether the interpersonal relationship (Partner vs Stranger), gender (Male vs Female), and visual feedback (Eye Contact vs Non-eye Contact) could modulate both the subjective experience and the autonomic responses of the person promoting an affective touch (hereafter also referred to as the “giver”). We measured hedonic responses while concomitantly tracking electro-dermal and cardiac activity. We hypothesized that participants would perceive more pleasant to caress their partner than a stranger, especially when the touch occurred during an eye contact exchange. On the contrary, stroking a stranger would result in an increase of autonomic responses as well as an increase of anxiety levels, and these effects might vary as a function of the giver’s gender as well as eye contact condition. To investigate whether the physiological responses observed in Experiment 1 could have been driven by eye contact alone or by any anticipatory effects, we conducted Experiment 2 where we manipulated these two variables. In Experiment 2 we first assessed whether affective touch combined with eye contact produced a larger autonomic response than eye contact alone, then if such effect was larger with a stranger compared to the partner, and finally whether there were any gender differences. Moreover, to control that the increase in skin conductance observed during affective touch was related to touch and not driven by any anticipatory effects due to the instruction participants received, we varied the instruction’s timing and removed any count-down so that participants could not predict the beginning of the touch. We hypothesized a stronger autonomic response when participants were engaged in an affective touch as compared to just mutual eye contact, as well as a higher hedonic experience when interacting with their partners as compared to a stranger. Additionally, we predicted that the increase in skin conductance during an affective touch would have been both independent from and larger than the physiological activity during the instruction period, thus, ruling out the possibility that the increase in skin conductance observed during affective touch could be driven by an anticipatory effect.