THE EFFECTS OF VISUAL-CORTEX LESIONS ON THE PERCEPTION OF ROTATED SHAPES

Monkeys with inferior temporal cortex lesions cannot discriminate betw een different shapes (e.g., + vs. 0) but can discriminate between shap es that differ only in orientation (e.g., 6 vs. 9). Lesions of the par ietal 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 conventiona l; any change in orientation disrupts performance. In this paper we ar gue 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 lesi ons reflect the relative contributions of the two areas to the task an d disrupt different stages of the two strategies used. A framework for the cortical processing of rotated shapes in the non-human primate is presented.