Active and passive-touch during interpersonal multisensory stimulation change self-other boundaries

In the “enfacement” illusion seeing an unfamiliar face being touched at the same time as one's own face evokes changes in self-face recognition. We investigated the contribution of proprioceptive and motor signals derived from self-generated actions in the sensory-driven malleability of self-other boundaries during the “enfacement” illusion. Changes in self-face recognition during active- and passive-touch interpersonal visuo-tactile stimulation were quantified by means of psychophysical and psychometric tasks. Active- and passive-touch evoked comparable changes in the categorical boundaries of self-other distinction, changing the extent to which the other is assimilated into the mental self-representation. Actively touching or simply feeling touch on one's own face with concurrent observed touch on someone else's face seems to elicit comparable changes in self-recognition, suggesting that afferent input might be sufficient for updating one's body-image, although some components of the experience of self-identification seem to be more affected by passive- than by active-touch.