Affective Touch is encoded by pupil dilation as a comprehensive social
phenomenon
Abstract
Affective Touch plays a pivotal role in regulating emotions, fostering
social bonds and nurturing affiliations with others. The emotional and
arousing dimensions associated to Affective Touch are linked to the
activation of the CT- fibres system, an afferent pathway attuned to
those specific features of tactile stimulations which characterize
gentle human caresses, such as touch velocity and the nature of the
stroking source. While previous research has examined the physiological
responses in relation to these individual features of Affective Touch,
no study has explored how they interact to shape autonomic activity. In
this study, we investigated whether and how touch velocity (CT-optimal
vs. CT-suboptimal) and the nature of the touching effector (Human hand
vs. Artificial hand) influenced the participants’ pupil dilation and
their subjective experience during tactile stimulation. We observed a
higher pupil dilation when touch was delivered simultaneously at
CT-optimal speed and by a human hand. This kind of touch invoked a
supralinear enhancement of pupil dilation indicating that the
combination of these two features induced a significantly stronger
autonomic activation than the summed effects of each delivered
separately. Moreover, this specific type of touch was perceived as the
most pleasant compared to all other tactile stimulations. Therefore,
pupil dilation appears to map the positive and pleasant experience of
human-to-human tactile interactions. Collectively, our results support
the notion that the autonomic nervous system encodes the emotional and
hedonic aspects associated with Affective Touch as a complex and
holistic social experience, rather than solely responding to its
low-level sensory properties.