OPTIC APHASIA - A REVIEW OF PAST STUDIES AND REAPPRAISAL

The existence of optic aphasia has been taken as strong evidence for a fractionation of knowledge representations into modality-specific systems (visual, tactile, etc.) in addition to verbal semantics. However, the multiplication of knowledge bases and the existence of unimodal aphasias has often come under severe attack. In this paper, the central issues concerning optic aphasia will be reassessed by looking more closely at modern reports and by interpreting them within a framework that allows for a fractionation of object knowledge. An overview of the literature showed that patients with a disorder of visual naming may be divided according to whether or not stimulus quality affects performance. A further analysis of these two groups was undertaken with respect to the retrieval of knowledge concerning colours of objects. It allowed us to reclassify optic aphasia as an impairment of a 'direct' route for visual naming. The 'direct' route is from the object's structural description to the phonological output lexicon without access to functional or associative object knowledge.