UNDERSTANDING AMBIGUOUS WORDS IN SENTENCE CONTEXTS - ELECTROPHYSIOLOGICAL EVIDENCE FOR DELAYED CONTEXTUAL SELECTION IN BROCAS-APHASIA

This study investigates whether spoken sentence comprehension deficits in Broca's aphasics results from their inability to access the subord inate meaning of ambiguous words (e.g. bank), or alternatively, from a delay in their selection of the contextually appropriate meaning. Twe lve Broca's aphasics and twelve elderly controls were presented with l exical ambiguities in three context conditions, each followed by the s ame target words. In the concordant condition, the sentence context bi ased the meaning of the sentence-final ambiguous word that was related to the target. In the discordant condition, the sentence context bias ed the meaning of the sentence-final ambiguous word that was incompati ble with the target. In the unrelated condition, the sentence-final wo rd was unambiguous and unrelated to the target. The task of the subjec ts was to listen attentively to the stimuli. The activational status o f the ambiguous sentence-final words was inferred from the amplitude o f the N400 to the targets at two inter-stimulus intervals (ISIs) (100 ms and 1250 ms). At the short ISI, the Broca's aphasics showed clear e vidence of activation of the subordinate meaning. In contrast to elder ly controls, however, the Broca's aphasics were not successful at sele cting the appropriate meaning of the ambiguity in the short ISI versio n of the experiment. But at the long ISI, in accordance with the perfo rmance of the elderly controls, the patients were able to successfully complete the contextual selection process. These results indicate tha t Broca's aphasics are delayed in the process of contextual selection. It is argued that this finding of delayed selection is compatible wit h the idea that comprehension deficits in Broca's aphasia result from a delay in the process of integrating lexical information. (C) 1998 El sevier Science Ltd. All rights reserved.