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Abstract:
Abstract: Animal studies have established the existence of
functionally distinct dorsal (parietal) and ventral
(inferotemporal) pathways in the brain, believed to encode
viewpoint-referenced and viewpoint-independent object information,
respectively. This study, based on an object recognition task
described by Tarr & Pinker (1990), aims to examine human brain
activation during preferential recruitment of each reference
system. Six normal right-handed subjects memorised 2-D novel shape
stimuli found to elicit (1) orientation-dependent or (2)
orientation-invariant time costs. Practice on canonically- and then
non-canonically oriented stimuli was followed by functional
magnetic resonance imaging (fMRI) scans during non-canonical
recognition of each stimulus type. 21 blood oxygen level-dependent
(BOLD) image slices representing the mean activation for conditions
(1) and (2) relative to rest were acquired and peak regions of
activation determined with reference to the stereotaxic brain atlas
of Talairach and Tournoux. Significant (p<0.02) widespread
activation of prefrontal, occipital, parietal and temporal regions
was observed in both conditions but preferentially in the caudate
nucleus and Brodmann's Areas 2 and 6 during the
orientation-dependent condition. We interpret these results as
implicating dorsal and ventral regions in the execution of both
tasks, and suggest that the observed premotor activation may
indicate motor planning behaviour analogous to 'mental rotation' of
the orientation-dependent stimulus shapes.
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