Visual object processing in optic aphasia: A case of semantic access agnosia

Abstract A single case study is reported of a patient with a naming disorder specific to visually presented stimuli. The patient was often able to gesture correctly to objects he could not name, and he showed intact access to structural knowledge of objects. Further examination revealed an impairment in accessing semantic knowledge about objects, which was most marked when the patient had to discriminate between objects which were visually as well as semantically similar. It is suggested that the patient's naming deficit is due to an impairment in accessing semantic information from vision, following intact access to stored structural knowledge. Correct gestures may be contingent on access to the system specifying structural knowledge. The data are interpreted in terms of a model of visual object identification in which access to semantic information, from the system specifying structural knowledge, is held to operate in cascade.