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Abstract:
In neuroimaging studies, category-specific semantic memory
organization has been mostly investigated during picture naming
tasks. However, it has been criticized that differences in
perceptual processing are the source of category-specific effects.
In this study we varied object category as well as modality
factorially. If category-specific effects reflect semantic memory
organization rather than differences in perceptual processing they
should be observed regardless of input modality. Subjects had to
verify the category of an target object (picture or object name)
from either an artifactual (e.g., tool) or natural category (e.g.,
animal) while event-related potentials were recorded from 64
channels. In the pictorial modality, at 160 ms after target onset,
natural categories elicited a greater visual N1 than artifactual
categories. This supports the assumption that perceptual
differences contribute to category-specific effects. Between
300-600 ms natural categories elicited over right occipito-temporal
areas a greater positivity than artifactual categories in both
modalities. This region has been identified as a major lesion site
for deficits in natural categories. In line with findings from
recent neuroimaging studies, artifactual categories were associated
with a greater positivity at left fronto-central electrodes. This
effect was only reliable within the pictorial modality. The results
suggest that semantic knowledge about different categories is
represented in multiple cortical areas which are at least partially
accessed regardless of input modality. Therefore, category-specific
effects cannot be exclusively explained by perceptual
sources.
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