The role of the vision in body perception: a study on hand distortions in blind and sighted individuals

Several studies have shown, in healthy individuals, the presence of large distortions for tactile stimuli represented on different body parts. Tactile distance between two touches on the dorsum of the hand is perceived as larger when they are oriented mediolaterally than proximodistally. Other studies showed that a temporary altered visual experience of the body affects perceived tactile distances. This is because the system tends to preserve tactile size constancy by rescaling the distorted body representation into an object-centred space, i.e., the body seen from the outside. This rescaling requires that the brain possesses a representation of the physical size of the stimulated body part. However, it is unclear what is the role of vision in tactile size constancy. Here, we investigated the role of vision in body representation, by asking congenitally and late blind individuals to estimate tactile distances between pairs of points on their hand dorsum and fingers. Results showed that irrespective of the visual experience, all groups of subjects exhibited the typical hand distortions. This suggests that visual information does not affect such representations. This challenges the notion that the rescaling of the distorted body representations tactile induced are made upon visual cues.