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Abstract:
Abstract: To test whether visual imagery evokes
content-specific patterns of activation in the ventral vision
pathway, we used fMRI while ten subjects performed perception,
imagery and control tasks. In the perception condition, subjects
passively viewed photographs of faces, houses, chairs and scrambled
pictures. In the imagery condition, subjects were instructed to
generate images of familiar faces, houses, or chairs from long-term
memory while viewing a gray square. In the control condition,
subjects passively viewed the gray square. Visual perception of
faces, houses, and chairs evoked differential patterns of response
in regions of ventral temporal cortex, as reported previously
(Ishai et al., 1999). Visual imagery activated small subsets of the
regions that responded differentially during perception. For each
category, activation during imagery was maximal in the same region
that responded maximally during perception. Perception and imagery
evoked activity with opposite patterns of hemispheric asymmetry,
with imagery evoking stronger response in left ventral temporal
regions, as indicated by both volume and amplitude of response.
Additionally, visual imagery evoked activity that was not
content-specific in the intraparietal sulcus, precuneus, caudal
anterior cingulate, and prefrontal cortex. We conclude that visual
imagery of objects from long-term memory is subserved by
content-specific activation in ventral temporal cortex, as well as
general activation in frontal and parietal regions which probably
mediate 'top-down' control of category-specific representations in
ventral extrastriate cortex.
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