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Abstract:
Abstract: To assess the perceptual independence of the
disconnected cerebral hemispheres, we presented bistable (Necker)
cubes simultaneously to the LVF and RVF of a callosotomy patient
under retinally-stabilized conditions. In a series of 1 minute
trials, the subject indicated the apparent orientation of the cube
in each VF by moving a joystick. A control condition with two
randomly-switching non-ambiguous cubes established he was capable
of performing well at such a dual tracking task. Results suggest
perceptual coupling, with a variable but reliable yoking of the
subject's left- and right-hand responses. However, results from
conditions in which the patient was presented with a reversing
non-ambiguous cube in one visual field and an ambiguous cube in the
other suggest this coupling is mediated by motor factors. When
responses were required to both the ambiguous and non-ambiguous
stimuli, reports of reversals in an ambiguous LVF stimulus tended
to mirror reversals in a non-ambiguous RVF stimulus. Since the
reverse pattern was not observed, this yoking appears to be driven
by the left hemisphere. In contrast, when the patient was
instructed to respond unimanually, reporting only the reversals of
the ambiguous stimulus, no significant yoking was found
irrespective of VF. Overall, outcomes suggest that in the absence
of a corpus callosum perceptual processes are potentially
independent in two cerebral hemispheres, but motor processes can
form a link between these perceptual systems.
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