IMPLICIT PROCESSING OF SOMATOSENSORY STIMULI DISCLOSED BY A PERCEPTUAL AFTER-EFFECT

A right-brain damaged patient (GR) showing tactile extinction, neglect and no hypesthesia, was asked to compare, in 30 trials, the size of t wo spheres of different size simultaneously put into each hand. Accura cy was poor because GR was unable to feel the sphere in his left hand and could only report the size of the right sphere. GR was then asked to compare two spheres of identical size: although again unable to per ceive the left sphere he was deceived b; a perceptual after-effect als o observed in normal subjects, and reported incorrectly the site of th e right sphere. The left sphere although unperceived influenced the pe rception of the right hand, thus giving the first evidence for an impl icit processing of extinguished somatosensory information.