Reaching with a tool extends visual-tactile interactions into far space: evidence from cross-modal extinction

Several recent studies have shown cross-modal visual-tactile extinction in patients with right hemisphere lesions. In the present case, patient BV, a visual stimulus close to the right hand extinguished awareness of a touch o n the left hand that would otherwise have been felt. Such extinction was re duced if the right visual stimulus was placed more distant from the patient 's hand in the radial plane. However, when the patient held sticks in both hands, so that a far right visual stimulus was now at the end of the "tool" in his right hand, cross-modal extinction from this far stimulus increased . This effect depended on the patient holding a stick that reached to the p osition of the far visual stimulus; a similar large stick, but not connecte d with the patient's hand and laying passively on the right, had no effect. Wielding the stick induced a re-mapping of space, so that the far light be came treated as near (and reachable by) the hand, thus modifying the spatia l nature of cross-modal extinction. This may relate to the properties of mu ltimodal neurons as found in the monkey intraparietal sulcus. (C) 2001 Else vier Science Ltd. All rights reserved.