The role of visual discrimination disorders and neglect in perceptual categorization deficits in right and left hemisphere damaged patients.

This study was designed to investigate the role of visual sensory deficits and neglect in perceptual categorization deficits in a group of 35 patients with unilateral cerebral lesions. From theoretical point of view, it was expected that right hemisphere lesions would play a critical role in eliciting perceptual categorization deficits which could not be accounted for by visual sensory deficits or neglect. The results revealed that perceptual categorization deficits were not confined to RHD patients, but they were also found in LHD patients. RHD patients were impaired regardless of the nature of the task (verbal vs. nonverbal), while LHD patients were impaired on nonverbal tasks, and in a lesser degree on verbal tasks. In both braindamaged groups, perceptual categorization deficits were highly associated with visual sensory deficits, however, perceptual categorization deficits were also found without impairments in the visual sensory system. Neglect to be less important determinant of perceptual categorization deficits. The present findings are discussed in the light of Warrington's model of object agnosia.