NEUROELECTRICAL CORRELATES OF AMBIGUOUS SENTENCE PROCESSING

A new approach to the study of event related potentials (ERPs) and language processing, the probe technique, was used to investigate the manner in which ambiguous sentences are processed. This technique involved recording ERPs to irrelevant light flashes while individuals were listening to auditorily presented sentences and performing sentence comprehension tasks. Since the ERPs were taken to light flashes, the ERPs should be independent of any acoustic or phonological characteristics of the sentences. Any differences in ERPs which occurred must then be due to differences in the manner in which individuals process sentences under different task conditions. It was predicted that differences in probe ERP components would provide support for a Prior Decision model of ambiguous sentence processing which states that both meanings of an ambiguous sentence will be accessed only when relevant context is not available for disambiguation. These differences reflecting sentence processing were expected to occur only over the left hemisphere.; Photic probe ERPs were recorded over left and right hemisphere frontal, parietal, temporal, and occipital recording sites of 24 adults during and immediately after presentation of ambiguous and unambiguous target sentences over a series of trials. During each trial, the target sentence was preceded by either relevant or neutral context sentence and followed by a true/false test sentence. Amplified ERPs for each subject were averaged and then submitted to a factor analysis procedure to identify factors that reflect the various components of the ERP waveform. The factor scores for each factor were then submitted to an analysis of variance to determine if any systematic differences occurred across experimental task. Contrary to predictions, both left hemisphere and bilateral ERP components, which differentiated ambiguous and unambiguous target sentences regardless of the type of preceding context, were obtained. These results were interpreted as providing some support for a Post Decision model of ambiguous sentence processing which suggests that both meanings of an ambiguity are accessed regardless of the presence or absence of relevant context. Also, the findings suggested that although the left hemisphere has a primary role in language processing, there is also some involvement of the right hemisphere.