PubMed · 4577659
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M L Espir. 1972. Visual agnosia.. https://pubmed.ncbi.nlm.nih.gov/4577659/
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Monkeys with inferior temporal cortex lesions cannot discriminate between different shapes (e.g., + vs. O) but can discriminate between shapes that differ only in orientation (e.g., 6 vs 9). Lesions of the parietal cortex, on the other hand, impair the discrimination of rotated shapes but spare the ability to discriminate between different shapes. A similar dissociation is found between some visual agnosics who can match but not identify rotated views of objects and other patients who can identify and discriminate objects only if the view is conventional; any change in orientation disrupts performance. In this paper we argue that two mechanisms may be available for the perception of rotated shapes. Which mechanism is used depends on the degree of rotation. It is suggested that the different effects of parietal and temporal lesions reflect the relative contributions of the two areas to the task and disrupt different stages of the two strategies used. A framework for the cortical processing of rotated shapes in the non-human primate is presented.
A patient of posterior cortical atrophy characterized by early signs of progressive visual agnosia documented by repeated neuropsychological tests, is reported. SPECT and MRI findings showed left unilateral parieto-occipital involvement in the earlier stage. A PET study executed eight months later showed bilateral parieto-occipital hypometabolism, but predominantly in the left hemisphere. This suggests that the degeneration may have developed asymmetrically, progressing from left unilateral to bilateral.