Abstract
Affective touch refers to the emotional and motivational facets of tactile sensation and has been linked to the activation of a specialised system of mechanosensory afferents (the CT system), that respond optimally to slow caress-like touch. Affective touch has been shown to play an important role in the building of the bodily self: the multisensory integrated global awareness of one’s own body. Here we investigated the effects of affective touch on subsequent tactile awareness and multisensory integration using the Somatic Signal Detection Task (SSDT). During the SSDT, participants were required to detect near-threshold tactile stimulation on their cheek, in the presence/absence of a concomitant light. Participants repeated the SSDT twice, before and after receiving a touch manipulation. Participants were divided into two groups: one received affective touch (CT optimal; n = 32), and the second received non-affective touch (non-CT optimal; n = 34). Levels of arousal (skin conductance levels, SCLs) and mood changes after the touch manipulation were also measured. Affective touch led to an increase in tactile accuracy, as indicated by less false reports of touch and a trend towards higher tactile sensitivity during the subsequent SSDT. Conversely, non-affective touch was found to induce a partial decrease in the correct detection of touch possibly due to a desensitization of skin mechanoreceptors. Both affective and non-affective touch induced a more positive mood and higher SCLs in participants. The increase in SCLs was greater after affective touch. We conclude that receiving affective touch enhances the sense of bodily self therefore increasing perceptual accuracy and awareness. Higher SCLs are suggested to be a possible mediator linking affective touch to a greater tactile accuracy. Clinical implications are discussed.
Highlights
When looking at change scores between Light and No Light trials, the CT optimal group showed a stronger decrease in c from No Light to Light trials (M = -.26, Standard Deviation (SD) = .22) compared to the non-CT optimal group (M = -.13, SD = .29; t(64) = -2.16, p = .035, d = .53). This last difference was no longer significant when using Bonferroni correction. These results indicate that all participants had a higher tendency to report perceiving the tactile pulse when the Light was present; this tendency was slightly stronger in the CT optimal group
Affective touch led to a decrease in false reports of feeling the tactile pulse (FA) during the Somatic Signal Detection Task (SSDT)
There was a tendency towards a main effect of group on d’, and exploratory analyses showed that sensitivity in detecting the tactile pulse (d) was significantly higher after receiving affective touch (CT optimal group) in comparison to after receiving non-affective touch
Summary
Activation of CT-afferents correlates with the subjective rating of pleasantness, indicating that CT-afferents may constitute the peripheral physiological substrate for pleasant tactile information [7, 9, 10] Because of their role in contributing to the hedonic value of social physical interactions, CT-afferents have been proposed to play a pivotal part in fostering affiliative behaviours and proximity seeking. Different streams of research converging in the so called ‘Social Touch Hypothesis’ have recently underlined the importance of CT-afferents in promoting social bonding and attachment [1, 11]. Supporting this hypothesis, it has been shown that CT-afferents respond optimally to touch delivered at skin temperature [8]. When asked to stroke babies or their partners, people spontaneously deliver touch at CT optimal velocities [12]
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