Barbiturate Nystagmus and the Mechanisms of Visual Fixation

Abstract

WHEN a human subject follows a moving object with his eyes, they perform movements of two types^1,2. There are smooth pursuing movements and rapid jerky changes of position known as saccades. Fig. 1a is a record of the position of an eye which is fixating a small spot of light in an otherwise totally dark room. Up to time t = 0 this spot of light has remained stationary in front of the subject. At time t = 0 it begins to move horizontally with a uniform velocity of 3 deg./sec. It can be seen that the eye remains stationary for about 150 msec., and then begins to move smoothly in pursuit of the spot. When about 300 msec. has elapsed since the spot began to move, the eye makes a saccadic movement at the end of which it is again looking directly at the spot. Thereafter the eye continues to move with the same velocity as the spot, and fixation is as good as it is when the spot is not moving.