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Abstract:
Humans and other animals have the ability to mentally
simulate transformations, such as changes in the orientation of
external objects and of their own bodies. Neuropsychological and
behavioral data suggest that imagined transformations of objects
may be computed in a different fashion from imagined
transformations of one's egocentric perspective. Initial results
from a blocked-design fMRI experiment were consistent with this
putative dissociation. Here we present new behavioral and brain
imaging data that further clarify the functional organization of
these mental spatial transformations. We asked observers to make
two kinds of judgments about pictures of human bodies with one arm
extended. Judgments of parity (same vs. different) about pairs of
identical or mirror-image bodies were predicted to give rise to
mental rotation of the figures. As is typically observed with
parity judgments of objects, response times increased as the
difference in orientation between the two figures increased.
Judgments of handedness (left vs. right) about the same figures
were hypothesized to induce an imagined egocentric perspective
transformation. The relationship between orientation and response
time for these judgments was reliably flattened compared to parity
judgments. As the tasks were performed, brain activity was recorded
with functional magnetic resonance imaging on a trial-by-trial
basis. Trials were averaged based on task, orientation, and
response time. Together with the chronometric results, the
functional data provide a picture of the component structure of
these two classes of mental spatial transformations.
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