Identification without manipulation: a study of the relations between object use and semantic memory

The role of semantic knowledge in object utilisation is a matter of debate. It is usually presumed that access to semantic knowledge is a necessary co ndition for manipulation, but a few reports challenged this view. The exist ence of a direct, pre-semantic route from vision to action has been propose d. We report the case of a patient with a disorder of object use in everyda y life, in the context of probable Alzheimer's disease. This patient was al so impaired when manipulating single objects. He showed a striking dissocia tion between impairment in object use and preserved capacity to perform sym bolic and meaningless gestures. To elucidate the nature of the disorder, an d to clarify the relations between semantic knowledge and object use, we sy stematically assessed his capacity to recognise, name, access semantic know ledge, and use 15 common objects. We found no general semantic impairment f or the objects that were not correctly manipulated, and, more importantly, no difference between the semantic knowledge of objects correctly manipulat ed and objects incorrectly manipulated. These data, although not incompatib le with the hypothesis of a direct route for action, are better accommodate d by the idea of a distributed semantic memory, where different types of kn owledge are represented, as proposed by Allport (Allport, D. A. Current per spectives in dysphasia, pp. 32-60. Churchill Livingstone, Edinbuirgh, 1985) . (C) 1998 Elsevier Science Ltd. All rights reserved.