Disorders of single word processing.

In recent years, studies in the cognitive neuropsychology of language have helped in understanding the functional architecture of linguistic processes. It has been shown that recognizing, comprehending and producing a word entails the activation of a complex set of mechanisms, each of which can be selectively impaired as a consequence of brain damage. Investigations of aphasic subjects have demonstrated that the meaning, the pronunciation and the spelling of a word are represented independently, that category information plays a critical role in semantic organization, and that the mental vocabulary represents word class and morphological structure. These distinctions in the architecture of the lexical-semantic system, in turn, have provided the basis for PET and fMRI studies of the neural correlates of single-word processing. These experiments, in agreement with recent neurophysiological investigations, suggest that cognitive/linguistic functions are likely to be represented in distributed neural networks often encompassing more than one lobe, rather than in individual, sharply demarcated neural structures.