Ac. Nobre et G. Mccarthy, LANGUAGE-RELATED ERPS - SCALP DISTRIBUTIONS AND MODULATION BY WORD TYPE AND SEMANTIC PRIMING, Journal of cognitive neuroscience, 6(3), 1994, pp. 233-255
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.