Visual perception is defective in probable DLB. The defective visual perception plays a role in development of visual hallucinations, delusional misidentifications, visual agnosias, and visuoconstructive disability charcteristic of DLB.

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Thirty-one patients with mild-to-moderate Alzheimer''s disease (AD) underwent a test battery of complex visual tasks. We assessed the scores using a principal-factor analysis to elucidate the underlying deficits. There were three independent factors: The first factor included the tasks of identifying and comparing forms of visual stimuli. The second factor consisted of digit span and digit symbol tasks, and the third factor consisted of a specified visual counting task. We considered these three factors as representing the dysfunctions of object recognition, general attention and spatial recognition, respectively. These results underline the disturbances of the two visual systems, object vision and spatial vision, in early-AD patients.

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