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Stephen Lomber, Erin Woller, Amee Hall, Bertram Payne; Neglected sight: Preserved visual functions within a neglected hemifield. Journal of Vision 2008;8(6):1006. doi: 10.1167/8.6.1006.
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In human subjects, damage of posterior parietal cortex in the right hemisphere often produces a neglect of visual stimuli in the left (contralateral) visual field. Unilateral removal or reversible cooling deactivation of the equivalent region in cats also results in an equally severe, if not greater, contralateral neglect and the cats cannot report the position of visual stimuli. In the current study, we tested for residual visual functions in four cats when they were forced to use the neglected field. To force use of the neglected hemifield, we divided the optic chiasm and forebrain commissures and placed a contact occluder over the left eye during cooling deactivation of right posterior parietal cortex lining the posterior middle suprasylvian sulcus. Under these forced conditions, all four cats could: 1) localize moving stimuli within the previously neglected hemifield; 2) perform direction of movement discriminations with differences greater, but not less than or equal to 30°; and 3) perform 3-D object and 2-D pattern discriminations. We conclude that, under free viewing conditions, the unimpaired hemisphere (and hemifield) dominates visual processing and control of visually-guided behavior. However, when visual input to that unimpaired hemisphere is blocked, the considerable visual processing within the neglecting hemisphere is revealed, and visual localization, some aspects of movement direction discrimination, and many aspects of form discrimination are all possible. In these regards, the split-brain preparation is a highly valuable experimental animal model system for investigating neglect of visual stimuli, and residual visual functions within the neglected hemifield.
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