Seeing where your hands are

Some patients with brain damage fail to identify a sensory stimulus presented on the opposite side to their lesion (contralesional) when a competing stimulus is presented on the same side (ipsilesional)1. This phenomenon has become known as extinction. It is commonly studied using a single sense such as sight or touch (unimodal extinction)2. We have studied a 75-year-old right-handed man (patient GS) who has severe left tactile extinction resulting from damage to the right frontotemporal cortex caused by a stroke. We found that an ipsilesional visual stimulus could induce extinction of a contralesional tactile stimulus (cross-modal extinction). We also found that the visual stimulus operates in a reference system attached to the hand, and not in egocentric coordinates (that is retinal, head or trunk-centred coordinates).