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Abstract:
We examined the ERP components sensitive to discourse-level
semantic processing of pictures and words. EEG was recorded from 29
scalp electrodes on 48 subjects who performed an anomalous story
task. Stimuli were series of pictures in which the final picture
was either congruous or incongruous with the preceding context,
written translations in which the final sentence was congruous or
incongruous, or cross-modal stories in which text story stems were
followed by congruous or incongruous final pictures. ERPs
time-locked to the onset of the final picture or final sentence
critical word were more negative for incongruous than congruous
items. For picture stories, two components were sensitive to
congruency: an earlier negativity (N300), distributed over central
and frontal sites, and a later negativity (anterior N400), also
with a centro-frontal maximum but more widespread and larger over
the right hemisphere. For text stories, the N400 effect had a
centro-parietal distribution (posterior N400). For cross-modal
stories, the effect was widespread (widespread N400). An N300 was
also present but did not show a congruency effect. These findings
suggest that the N300 and N400 are distinguishable components,
manifestation of an N300 is specific to pictures, and modulation of
this N300 also requires a pictorial context. These experiments also
revealed that the N400 can be modulated by discourse-level
coherence manipulations. Finally, the different scalp topographies
for pictures and text imply the activation of distinct brain
regions.
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