Somatosensory extinction for meaningful objects in a patient with right hemispheric stroke

Implicit: high level processing of extinguished objects has often been desc ribed in the visual modality. In the tactile domain, however, research on t his topic is meagre and it is still uncertain whether processing of tactual ly presented stimuli can be affected by the same attentional disorders as v isual stimuli. In this paper we describe a patient, ENM, with visual neglec t and light touch extinction who, in a naming task of objects presented in the tactile modality, simultaneously to both hands, showed extinction for l eft hand objects. He was, nevertheless, able to make above chance Same/Diff erent judgements on the two stimuli. We also tested two neurologically inta ct subjects who performed the test wearing a ski-glove on the left hand to impair the recognition of left hand objects. In these subjects, Same/Differ ent judgements were at chance level when recognition rate was as low as tha t found in patient ENM. This happened when either the objects, although sha ring the same name were different in shape (conditions Same-Different) or w hen the two objects were different with respect to the category name but we re actually physically similar (conditions Different-Similar). However, whe n the objects were either identical or completely different. i.e., in a con dition where judgement could be based simply on the physical analysis of th e object shape (condition Same-Identical and Different-Dissimilar), their S ame/Different judgements were above chance, despite the tactual deficit. Ou r conclusion was that patient ENM showed implicit recognition of left hand objects, at least in the Same-Different and in the Different-Similar condit ions, whereas, in the same conditions, normal subjects with an artificial s ensory impairment did not. Our results also show that Same/Different judgem ents may be, in some conditions, less demanding than naming tasks, as sugge sted by Farah et ar. Furthermore, patient ENM performed the test both with uncrossed and crossed hands. We found that extinction always affected the hand controlateral to the brain damage, although there was a tendency for a decrement of the ipsi lesional hand performance in the crossed condition. We discuss these findin gs with reference to the most recent theories on the existence of a body ce ntered spatial frame of reference. (C) 1999 Elsevier Science Ltd. All right s reserved.