Neural Limitations of Visual Excitability: Alterations Produced by Cerebral Lesions

Primary visual defects are usually defined as areas of complete or relative blindness (anopia or amblyopia) which are precisely localized in the field upon perimetric examination. Studies of patients with brain lesions have shown that the location and extent of such defects in the plotted field generally correlate with the locus and degree of damage in the geniculocalcarine system (Holmes and Lister, 1916; Spaulding, 1952, a, b ). In conjunction with relevant anatomical (Polyak, 1932) and electrophysiological (Marshall and Talbot, 1942) data, these findings have led to the concept of a strict spatial (topological or point-for-point) projection of visual function from retina to cerebrum (Marquis, 1935: Polyak, 1957). Where special testing methods have been used to supplement the clinical examination, alterations in vision have been reliably demonstrated in portions of the field which appear spared upon perimetry. Such findings have been interpreted