The possibility of exploiting optic nystagmus as an aid in cerebral localization depends on the fact that in certain cerebral lesions optic nystagmus may be present to one direction of movement of visual objects, but absent or defective in the other direction. This type of ocular behavior has been studied clinically by direct observation of the response of the eyes of a stationary subject to a moving visual field, such as a revolving drum or cylinder carrying alternate black and white stripes or a continuous series of figures or pictures. The test can be easily employed with practically all patients, providing they are sufficiently alert to direct their gaze to the drum. Optic nystagmus can be elicited with a low degree of visual acuity and even in the presence of a large central scotoma. Furthermore, hemianopic defects in the visual field, particularly those caused by infrageniculate lesions involving the optic