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Abstract:
Conceptual knowledge is thought to be represented in a large
distributed network, organised according to different types of
semantic features (e.g. visual, auditory, functional). We
investigated this theory, using PET, by contrasting brain activity
elicited by heard words with either (i) visual (eg BLUE), (ii)
auditory (e.g. NOISE) or (iii) abstract (e.g. TRUTH) content. The
activation task was either repetition or semantic decision (e.g.
does the meaning of the word relate to religion?). In the baseline
conditions, the sound track of the words was reversed and subjects
had to say "Okay" or make an acoustic decision (male voice?).
Irrespective of condition, words relative to their corresponding
controls activated the left posterior inferior temporal and
inferior frontal cortices. Activation specific for semantic type
was only observed in the left anterior temporal pole which
selectively responded to semantic decisions on words with visual or
auditory content. These results indicate a segregation of the
neural correlates for sensory and abstract semantic knowledge. They
are also consistent with neuropsychological studies showing that
anterior temporal lobe damage can cause deficits for items that are
mainly defined by their sensory features (i.e. concrete,
particularly living items). Our study therefore provides further
evidence for the feature-based account of semantic memory.
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