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Abstract:
Abstract: Studies of patients with visual apraxia and optic
aphasia suggest that an object can prompt a specific action
response (e.g. pour) either through analysis of its visual
structure, (its component parts, e.g. a spout,) or from related
semantic knowledge, and that these abilities can be dissociated.
This implies different neural routes to action that incorporate
specialized regions. We scanned six normal subjects with PET
(H2O15) while they mimed actions (constrained to 'twist' or
'pour'), to pictures of familiar objects or their names (written
words). To control for perceptual and motor aspects of the tasks,
subjects performed a size decision task for object pictures and
object names alike. Data were analyzed using statistical parametric
mapping (http//www.fil.ion.ucl.ac.uk/spm). The results identified
an action retrieval system that is common to both pictures and
words in left inferior frontal cortex (BA 44/45) and left posterior
temporal cortex (BA 37). Action retrieval to words also engaged
regions of the left temporal cortex that have been associated with
semantic processing of objects. For action retrieval to pictures of
objects, there was enhanced activation in the left lateral
occipital area, thought to be associated with structural
processing. We interpret these results in terms of there being a
semantic and a visual route to actions for objects.
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