Neuropsychological studies of verbal semantic systems

Abstract The selective impairment of verbal comprehension in patients with cerebral lesions provides a powerful and direct source of evidence regarding the properties of verbal semantic systems. Word frequency is shown to be an important determinant of performance for both spoken and written word comprehension, indicating that the aphasic patient may have a quantitative reduction in capacity according to task difficulty. But this cannot be an exhaustive account. Evidence for the vulnerability of subordinate as compared with superordinate information is reported, which it is argued indicates that the semantic representations of single words are hierarchical or ordered in their degree of specificity. Finally, evidence is presented for selective impairments of the comprehension of words from particular semantic categories. Double dissociations of deficits of the concrete-abstract and of objects-non-object concepts are reported. It is argued that the verbal semantic meaning systems are categorically organized