Agnostic Alexia without Agraphia Following Trauma

Abstract

Agnostic alexia is an infrequent form of aphasia and is a variety of visual agnosia (mind blindness). It is a disturbance of language function consisting of failure of recognition of the conventional meaning of graphic symbols, and may include inability to read letters, syllables, words, musical notes, and mathematical figures. The terms alexia and word blindness, which are most frequently used for this con­ dition, are somewhat objectionable in that inability to read may depend on many differ­ ent focal cerebral defects. Agnostic alexia is more specific for it is used in contradis­ tinction to aphasie alexia and semantic alexia. In aphasie alexia there is loss of ability to comprehend statements of a simple character, the words being properly recog­ nized. In semantic alexia the patient is un­ able to comprehend complicated statements while retaining the ability to grasp simple ones. The act of seeing is a highly complicated procedure requiring the integrity of the optic apparatus and a considerable part of the cerebral cortex. Much of the mechanism of how it is accomplished is conjectural and controversial, and its study involves the fields of anatomy, physiology, and psychol­ ogyExperimental and clinical investigations have proved that the calcarine area (area 17 of Brodmann) of the occipital lobe is the site of the primary cortical termination of the visual impulse. Neurons from the retina maintain a precise spatial organization in their course to the external geniculate body and thence to the calcarine cortex, thereby producing point to point retinal representa-