The double dissociation between the knowledge of gestures and the actual object use. A study of two patients

Concerning the debate about the relationship between gesture representation related to tools and semantic action knowledge, we focus our attention on the gesture concepts necessary for performing a skilled tool-use and on their possible nature, semantic versus presemantic. We present 14 patients who were examined for praxis abilities with our Apraxia Battery and discuss their performance related to most common cognitive model for praxis. 14 patients with different etiology (6 cortico-basal disease, 1 possible Alzheimer’s disease with atypical onset and 7 left hemispheric strokes) perform an Apraxia Battery composed of 8 tasks (semantic questionnaire, denomination task, verbal recognition tasks, utilization apraxia task, pantomime comprehension , gesture similarity judgment, functional-manipulation similarity judgment, and De Renzi’s imitation test for ideomotor apraxia). All the degenerative patients underwent to a general neuropsychological examination to assess the cognitive profile and the patients with stroke received the Token Test to assess the present of aphasia. Among all patient, we found two patient who present an opposite performance on GSJ task and the manipulation part of the FMSJ one. The patient A (CBD patient) and B (left thalamic stroke patient) performs normal in manipulation similarity judgment part, while shows difficulties in GSJ. On the other hand patient C (CBD patient) shows the opposite pattern (pathological performance in GSJ and preserved abilities in MSJ task. As we suppose, Gesture Similarity Judgment task examine the gesture representations through a semantic route by verbal modality, while the Manipulation Similarity Judgment task explores them though a direct visual modality. We believe that patient A and B present unimpaired gesture representations to a presemantic level, but show a possible deficit at semantic level or a interrupted link between action semantic knowledge and peripheral representations.