The study of patients with focal lesions of the central visual system has shown that certain forms of complex visual disturbance are generally associated with lesions in the inferior aspect of that system (the inferior occipital lobe and adjoining temporal lobe), while other disturbances are more commonly associated with lesions of the superior aspect of that system (the superior occipital cortices and adjoining parietal lobe). Each of these systems appears to contain cortical regions specialized in the processing of salient features such as shape, color, stereopsis and motion, and in general the dichotomy also relates, respectively to object and spatial processing. The principal aims of this project are to increase our knowledge regarding the presumed inferior/superior diversity of human visual function with respect to a vertical axis about the calcarine fissure. We also aim to study new aspects of the organization of human vision beyond the relatively early stages at which processing asymmetries for basic visual functions are evident. We will test a series of hypotheses by conducting systematic experiments in a large number of subjects (newly referred or from the Database/Registry) with damage in various components of neural systems underlying vision. The anatomical study is based on a standardized analysis of CT and MR data. The behavioral study consists of a core of basic neuropsychological tests, neuro-ophthalmological screening procedures and psychophysical paradigms. The new experiments are aimed at testing hypotheses on (a) visual search with eye movements; (b) orienting and sustaining of attention, and the role of attention in the search for feature conjunctions; (c) reaching and grasping of external targets; (d) processing of motion, and its combination with stereopsis to determine the structure of 3-D objects; and (e) processing of color. The study should contribute to our understanding of the modular organization of the visual system at a telencephalic level. By studying vision and its neural substrates revealed in patients with cognitive impairments due to focal brain lesions, it may be possible to devise better strategies to diagnose and manage those impairments.
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