LANGUAGE-RELATED ERPS - SCALP DISTRIBUTIONS AND MODULATION BY WORD TYPE AND SEMANTIC PRIMING

Event-related potentials (ERPs) were recorded from the scalp to invest igate the processing of word stimuli. Three tasks were used: (1) a tas k comparing words that provided an anomalous or normal sentence ending , (2) a word-list task in which different word types were examined, an d (3) a word-list task in which semantic priming was examined. ERPs we re recorded from a 50-channel montage in an attempt to dissociate over lapping ERP features by their scalp distributions. The focus of these studies was the N400, an ERP previously associated with language proce ssing (Kutas & Hillyard, 1980). The temporal interval typically associ ated with N400 (250-500 msec) was found to contain overlapping ERP fea tures. Two of these features were common to both sentence and word-lis t tasks-but one appeared different. Anomalous sentence endings and wor ds with semantic content in lists both showed coincident negative left frontotemporal and midline-anterior ERP foci, peaking at 332 msec for sentences and 316 msec for word lists. The most negative voltage obta ined in the sentence task peaked at 386 msec and had a midline-posteri or focus. A right fronto-temporal focus developed after the midline-po sterior focus and outlasted its duration. The most negative voltage fo r content words in lists was reached at 364 msec. The distribution of this ERP was extensive over the midline and appeared to differ from th at observed in the sentence task. Modulation of language-related ERPs by word type and semantic priming was investigated using die word-list tasks, which required category-detection responses. Two novel finding s were obtained: (1) The ERP distributions for words serving grammatic al function and content words differed substantially in word lists. Ev en when devoid of any sentence context, function words presented signi ficantly attenuated measures of N400 compared to content words. These findings support hypotheses that suggest a differential processing of content and function words. (2) Semantic priming functionally dissocia ted two ERP features in the 250-500 msec range. The later and most neg ative midline ERP feature (peaking at 364 msec) was attenuated by sema ntic priming. However, the earlier left frontotemporal feature (peakin g at 316 msec) was enhanced by semantic priming. The isolation of this novel language-related ERP that is sensitive to semantic manipulation s has important consequences for temporal and mechanistic aspects of t heories of language processing.