Residual Visual Function after Brain Wounds involving the Central Visual Pathways in Man

Abstract

IT is generally believed that total destruction of visual cortex and optic radiations in man should lead to blindness, and that regional (subtotal) destruction should correspondingly produce circumscribed areas of blindness (“scotomata”) in the visual field¹. Such areas of blindness are defined by a patient's inability to detect and report visual stimuli projected into the affected region. Standard methods of visual field testing (perimetry) suggest that such scotomata may be “absolute”, that is the patient seems to be unable to distinguish between the presence and absence of visually presented targets whenever they are presented in the scotomatous area. Suspecting that the response of the visual system may depend on the task requirements, we used a technique which requires a localizing response from the patient², in addition to clinical perimetry. As a result, we have found evidence for the processing of information about the locus of light stimuli presented in areas of the visual field which are “blind” by the traditional definition.