Discrimination of normal and aphasic subjects on a test of syntactic comprehension.

An Anglophone population consisting of 37 aphasic patients and 23 normal control subjects, and a Francophone population consisting of 49 aphasic patients and 23 control subjects were given a task requiring the comprehension of syntactic structures for the correct assignment of thematic roles to nouns. Discriminant analysis was used to classify subjects into aphasic and normal groups according to their scores on the task. In both populations--Anglophone and Francophone--most of the subjects were classified into their actual groups except for an occasional normal subject classified with the aphasic group and a small number of aphasics classified as normal. A cut-off score below which performance is clearly abnormal and above which performance is clearly normal can be set for this test. Patients who performed normally on this test had lesions affecting any single lobe within the dominant perisylvian cortex and mostly consisted of patients with dysarthria, apraxia of speech, and 'mixed' aphasia types. The results have implications for the incidence of aphasic disturbances of syntactic comprehension and for the nature of language representation in the brain.