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Abstract:
Evidence suggests that visual processing is divided into two
pathways: the 'ventral stream' that is specialized for object
recognition (the "what" system) and the 'dorsal stream' that is
specialized for the visual guidance of action (the "how" system).
We investigated the possible dissociation of the two cortical
visual systems in children with Williams syndrome (WS), a rare
genetic disorder that results in a unique cognitive profile
including impaired spatial cognition, together with relatively
spared language. Following Milner & Goodale (1995), we compared
performance in an action task (Posting) to that in a perceptual
task (Matching). In the Posting task, children were instructed to
post a card into a slot oriented to 0, 45, 90, or 135 degrees. In
the Matching task, they judged when a card was aligned such that it
would fit into the slot. The results of Experiment 1 showed
breakdown in the Posting task among WS children relative to
normally developing mental age-matched children. The results of
Experiment 2, in which a 5 second delay was imposed between viewing
the slot and Posting or Matching, showed additional and
disproportionate breakdown in Posting among WS children. These
results are consistent with the hypothesized division of labor in
the visual system, and the selective impairment of the action
system in Williams syndrome.
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