Neuropsychologic analysis of the abnormalities of speech and language production in patients with cerebral lesions reveals clear dissociations between different processes. These dissociations are similar to ones predicted by linguistic theory, lending further support to the validity of linguistic theoretical constructs. Moreover, the specific relation of certain types of disruptions to certain areas or types of brain damage suggests that different processes are subserved by separable neuronal subsystems. Distinct disorders range from those involving purely phonological motor mechanisms (dysarthrias) through those involving syntactic processes (agrammatism), the semantic-lexical interface (anomia), and general semantic pre-verbal processes (some cases of dementia). In addition, disorders of the supralinguistic process of planning for speech intentions are seen in some other cases of dementia and in lesions of the frontal lobes. Parallelisms and divergencies between motor acts and speech production are briefly discussed.
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