SHAPE INTEGRATION FOR VISUAL OBJECT RECOGNITION AND ITS IMPLICATION IN CATEGORY-SPECIFIC VISUAL AGNOSIA

series of experiments was conducted on a patient (ELM) with bilateral inferior temporal lobe damage and category-specific visual agnosia in order to specify the nature of his functional impairment. In Experimen t 1, ELM performed a task of picture/word matching that used line draw ings of fruits and vegetables as stimuli. The pattern of confusions ex hibited by the patient suggested a failure in processing the full rang e of shape features necessary for the unique specification of the targ et relative to other structurally related items. This hypothesis of a shape integration impairment was tested and verified by subsequent vis ual recognition experiments (Experiments 2-4), which used synthetic st imuli with shapes precisely defined on the dimensions of elongation, c urvature, and tapering. Futhermore, it was determined (Experiment 5) t hat the integration deficit is specific to the retrieval of shape know ledge from memory and does not affect the encoding of the properties o f visual stimuli. It is argued that these findings have critical impli cations for cognitive theories of visual object recognition and for an interpretation or the visual function of the inferior temporal cortex . Finally, it was shown that the patient's deficit for structural know ledge integration is modulated by the semantic properties of the objec ts (Experiment 6), thereby demonstrating the applicability of the pres ent findings to an explanation of category-specific visual agnosia.