[Associative visual agnosia: role of the left hemisphere in visual perception (author's transl)]

Visual agnosia following ischaemic accidents of the left posterior cerebral artery is often associated with intellectual deficiencies, memory disorders, elementary perceptive disturbances and elements of visuoverbal disconnection, with the result that some authors reject the notion of visual agnosia. By using a relatively simple examination procedure it is, however, possible to clearly differentiate the various disturbances, as shown by the case of a right-handed 66-year-old man in whom this type of vascular accident occurred. Neither the reduced intellectual capacities nor the memory disorders can explain the differences observed in the treatment of visual stimuli, which was very disturbed, and the normal treatment of other types of stimulus. Elementary difficulties are not sufficient to prevent correct discrimination, as all tests of matching object, images, colours, and graphic signs were successfully accomplished. Identification was disturbed however: the patient could not show the use of objects presented visually, and this disorder is related to the visual characteristics of the stimuli, which excludes a simple visuogestural disconnection; results of tests of classifying types of object images, colours, and graphic signs were markedly abnormal. Naming of these stimuli was also affected, even when they were correctly identified; this results from the visuoverbal disconnection associated with the agnosia, but it is insufficient to account for it, as the patient could correctly use objects that had been wrongly named, but could not use those that had been poorly identified. This case, therefore, has enabled a visual identification disorder to be isolated independently from a discrimination problem, and visuoverbal or visuogestural disconnections. It is the significance of ths stimulus that is disturbed. In contrast, functional or categorical classification is respected in right temporo-occipital lesions. It is the individuality of a stimulus within a physical category which is disturbed.