Seeing and feeling for self and other: proprioceptive spatial location determines multisensory enhancement of touch.

We have investigated the relation between visuo-tactile interactions and the self-other distinction. In the visual enhancement of touch (VET) effect, non-informative vision of one's own hand improves tactile spatial perception. Previous studies suggested that looking at another person's hand could also enhance tactile perception, but did not systematically investigate the basis of this effect. In experiment 1 we manipulated the spatial location where one's own or another person's hand was seen. Viewing one's own hand enhanced tactile orientation discrimination relative to viewing a neutral object, but only when the visual image of the hand was spatially aligned with the actual location of the participant's unseen hand, as signaled by proprioception. In contrast, viewing another person's hand produced enhanced tactile perception irrespective of spatial location. In experiment 2, we used a multisensory stimulation technique, known as visual remapping of touch (VRT), to reduce the spatial misalignment between the visual and proprioceptive locations of the hand. Participants saw an image of their own hand being touched at the same time as the tactile stimulation, which reduces perceived misalignment. This spatial adaptation procedure caused the VET effect to return. Our results suggest that multisensory modulation of touch depends on a representation of one's own body that is fundamentally spatial in nature. In contrast, representation of others is free from this spatial constraint.