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Abstract:
We perceive a stable visual world despite the fact that our
eye movements bring a new image onto the retina every ~300ms. This
perceived spatial constancy is thought to emerge from a dynamic
updating of visual representations, which takes into account our
voluntary eye movements. Neurons in parietal cortex, frontal cortex
and superior colliculus have been shown to update visual
representations in conjunction with saccades. This spatial updating
is required in the double step task, in which the animal makes
sequential saccades to two remembered target locations. To acquire
the second target accurately, the spatial representation of the
stimulus must be updated to account for the first saccade. To test
whether the corpus callosum is necessary for spatial updating, we
measured performance in the double step task in a rhesus macaque
whose corpus callosum and anterior commissure were resected. Two
conditions of the double step task were tested: 1) across-hemifield
sequences, in which the second target was updated from one visual
hemifield to the other, and 2) within-hemifield sequences, in which
the second target was updated within a hemifield. Initial
performance was impaired for across-hemifield but not
within-hemifield sequences. The across-hemifield sequences could be
learned, however, as the animal gained experience with specific
sequences. These results indicate that updating can occur in the
absence of the forebrain commissures, suggesting that subcortical
pathways are sufficient for updating spatial information across
hemifields.
Supported by: NEI; NSF; McDonnell, EJLB and Whitehall
Foundations.
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