""""""""Blindsight,"""""""" the ability of certain patients with striate lesions to make judgments regarding visual stimuli they claim they cannot see, has been attributed to visual pathways which bypass the striate complex. It has also been argued that blindsight could be due to vestiges of functioning primary cortex. In accord with this latter possibility, Fendrich, Wessinger & Gazzaniga recently reported a small and isolated island of blindsight in a hemianopic patient. Because this patient's residual vision is limited to a very restricted retinal region, a corresponding island of spared visual cortex is its probable source. This finding raises the possibility that other instances of blindsight maya be mediated by similar islands. In the first part of Project 1, we propose to evaluate this hypothesis by carrying out a perimetric mapping program (using an interval 2 alternative forced choice task) to search for similar spared regions in additional hemianopic patients. Abilities (such as localization) which have been attributed to blindsight will be assessed both within and outside such regions. In this manner, the general dependence of various manifestations of blindsight on surviving cortex can be appraised. Finally, we will attempt to identify the anatomical locus of the cortex mediating regions of spared function using MRI and VEPs. The second part of Project 1 investigates various patient groups for impairments of the visual constancies which produce the percept of a stable world despite retinal image transformations. Although there is a long history of research on the operation of these constancies, little is known regarding their neural substrate. However, recent physiological studies in monkeys have suggested that position constancy--the apparent stability of positions despite the image displacements produced by eye motions--may be mediated by the parietal lobes. We propose to test this hypothesis by testing parietal patients on tasks designed to assess visual stability during eye motions and the stability of perceived spatial locations with different angles of gaze. In addition, no investigations have been carried out with neurological patients to psychophysically appraise deficits in the constancies of size and shape, although studies of """"""""object constancy"""""""" suggest such deficits may occur. Based on the available human data and animal lesion studies, patients with lesions affecting inferotemporal cortex, and the right parietal lobes are candidates for showing such impairments. We propose to evaluate the constancies of size and shape in patients with focal lesions in these areas.
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