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 condition for manipulation, but a few reports challenged this view. The existence of a direct, pre-semantic route from vision to action has been proposed. We report the case of a patient with a disorder of object use in everyday life, in the context of probable Alzheimer's disease. This patient was also impaired when manipulating single objects. He showed a striking dissociation between impairment in object use and preserved capacity to perform symbolic and meaningless gestures. To elucidate the nature of the disorder, and to clarify the relations between semantic knowledge and object use, we systematically assessed his capacity to recognise, name, access semantic knowledge, and use 15 common objects. We found no general semantic impairment for the objects that were not correctly manipulated, and, more importantly, no difference between the semantic knowledge of objects correctly manipulated and objects incorrectly manipulated. These data, although not incompatible with the hypothesis of a direct route for action, are better accommodated by the idea of a distributed semantic memory, where different types of knowledge are represented, as proposed by Allport (Allport, D. A. Current perspectives in dysphasia, pp. 32-60. Churchill Livingstone, Edinburgh, 1985).