SPOKEN SENTENCE COMPREHENSION IN APHASIA - EVENT-RELATED POTENTIAL EVIDENCE FOR A LEXICAL INTEGRATION DEFICIT

In this study the N400 component of the event-related potential was us ed to investigate spoken sentence understanding in Broca's and Wernick e's aphasics. The aim of the study was to determine whether spoken sen tence comprehension problems in these patients might result from a def icit in the on-line integration of lexical information. Subjects liste ned to sentences spoken at a normal rate. In half of these sentences, the meaning of the final word of the sentence matched the semantic spe cifications of the preceding sentence context. In the other half of th e sentences, the sentence-final word was anomalous with respect to the preceding sentence context. The N400 was measured to the sentence-fin al words in both conditions. The results for the aphasic patients (n = 14) were analyzed according to the severity of their comprehension de ficit and compared to a group of 12 neurologically unimpaired age-matc hed controls, as well as a group of 6 nonaphasic patients with a lesio n in the right hemisphere. The nonaphasic brain damaged patients and t he aphasic patients with a light comprehension deficit (high comprehen ders, n = 7) showed an N400 effect that was comparable to that of the neurologically unimpaired subjects. In the aphasic patients with a mod erate to severe comprehension deficit (low comprehenders, n = 7), a re duction and delay of the N400 effect was obtained. In addition, the P3 00 component was measured in a classical oddball paradigm, in which su bjects were asked to count infrequent low tones in a random series of high and low tones. No correlation was found between the occurrence of N400 and P300 effects, indicating that changes in the N400 results we re related to the patients' language deficit. Overall, the pattern of results was compatible with the idea that aphasic patients with modera te to severe comprehension problems are impaired in the integration of lexical information into a higher order representation of the precedi ng sentence context.