Visuoperceptual function in visual agnosia.

Two patients with visual agnosia underwent visual recognition and neuropsychological tests to characterize their perceptual functioning. Both had an initial "apperceptive profile" and evolved from cortical blindness. One had carbon monoxide intoxication and incidental agenesis of the splenium of the corpus callosum; the other had the clinical features of MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like syndrome). The agnosia profile showed impaired object recognition but adequate visual matching and copying of unrecognized items. The patients were successful on form discrimination, mental rotation, and visuospatial skills, but did poorly on figure-ground discrimination, visual integration, facial discrimination, and constructional tasks. Their performances were characterized by slow, serial analysis of visual features and a decreased useful field of view. The pattern of results suggests a form of visual agnosia caused by disturbances of parallel distributed processing.