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Abstract:
Visual words, auditory words, pictures . . . all can be used
to represent the same concept and, in electrophysiological studies,
all are associated with a negativity 300-500 millisecond
post-stimulus onset ("N400") that varies in amplitude with
expectancy. However, these three types of stimuli are processed by
different neural systems (which may explain the distributional
differences observed to each) and represent information with
differing degrees of explicitness. In this series of studies, we
examined the functional similarity of the N400 response to these
three stimulus types. We recorded event-related potentials (ERPs)
as volunteers read/listened to pairs of sentences for
comprehension. The first sentence (e.g., "He caught the pass and
scored another touchdown.") set up an expectation for a particular
exemplar of a particular category ("sports"), while the second
("There was nothing he enjoyed more than a good game of ...") ended
with (1) the expected item ("football"), (2) an unexpected item
from the expected category ("baseball"), or (3) an unexpected item
from an unexpected category ("chess"). Target items were visual
words (Exp. 1) or pictures (Exp. 2) in the reading condition and
auditory words (Exp. 3) in the listening condition. All unexpected
items elicited an N400. For all words, but not for pictures, N400
was intermediate in amplitude if the unexpected item was from the
expected category. The nature of long-term memory access (as
indexed by the N400) thus seems to be modality-independent for
words but to differ functionally for pictures.
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