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Abstract:
Abstract: The impairment that patients show for specific
categories of knowledge seems to occur at different stages of the
object naming process. In most cases there is a clear disorder at
the semantic level, which also causes a lexical retrieval
impairment. In others, despite little evidence of an underlying
semantic damage, a noticeable lexical retrieval deficit is still
present. We used PET to investigate which of these levels of object
processing generate category specific effects. Eight healthy
volunteers were scanned while naming or reading the name of
visually presented stimuli belonging to six different categories:
famous faces, animals, manmade objects, body parts, maps and
colours. If category specificity arises at the lexical retrieval
level, we would expect greater differences between categories in
the naming than in the reading condition. This was not observed.
Differences were found only when naming and reading were considered
together. Stimuli with greater visual complexity (famous faces,
animals and maps) enhanced activation in the left extrastriate
cortex. Map recognition, which requires greater visuo-spatial
processing, activated right occipito-parietal and parahippocampal
cortices. These effects emphasise differences in the perceptual
processing of pictorial stimuli. At a semantic level, activation
was enhanced in the left lateral temporal cortex, anteriorly for
famous faces and posteriorly for manmade objects and body
parts.
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