PubMed · 6474020
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A M Eber. [Electrooculography].. https://pubmed.ncbi.nlm.nih.gov/6474020/
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We have evaluated a video-based method for measuring binocular horizontal and vertical eye movements of human subjects by comparing it with the magnetic search coil technique. This video tracking system (VTS) uses multiple infrared light sources and small video cameras to simultaneously measure the positions of reflected corneal images and the center of the pupil. The system has a linear range of approximately +/- 40 degrees horizontally and +/- 30 degrees vertically, a sampling rate of 120 Hz (180 Hz with the head fixed), and system noise with standard deviation of < 0.04 degree. The binocular eye-tracking system is light-weight (190 g), being mounted on goggles that, with the eyes in primary position, permit a field of view of 60 degrees horizontally and vertically. The VTS is insensitive to translations of the tracker relative to the eyes. By placing the video preprocessing unit on a cart, eye movements may be recorded while subjects walk through distances up to 100 feet. In comparison with the magnetic search coil technique, the VTS generally provides reliable measurements of horizontal and vertical eye position; eye velocity is noisier than corresponding coil signals, but superior to electro-oculography.
1. Anticipatory saccades in smooth pursuit move the point of gaze from near the moving target to well ahead of it, interrupting accurate smooth pursuit. Their effects on the pursuit process were studied in 22 normal human subjects. We presented horizontal periodic target trajectories of 30 degrees amplitude and 30 degrees/s constant velocity or 0.4 Hz sinusoidal velocity in 40-s trials. Saccades and surrounding smooth eye movement (SEM) segments were marked and classified by computer. 2. Anticipatory saccades were often followed by slowed SEM that tended to intercept the target at the endpoint of its trajectory. This was seen in the distribution of projections of the initial 60 ms of postsaccadic SEM to the time of the trajectory endpoint. Magnitude of this SEM tended to follow a function of the time and location of the endpoint of the anticipatory saccade, decreasing as the anticipatory saccades landed closer to the trajectory endpoint. 3. The time and location of the target trajectory endpoint seemed to be the goal for this SEM. We believe this to demonstrate the predictive use of the period and amplitude of the trajectory in smooth pursuit, apart from the instantaneous velocity match of the target. 4. Gottlieb and coworkers in the frontal eye field and Ron and Robinson in the cerebellum produced SEMs in the monkey by microstimulation. At some sites in both structures, direction and velocity of the SEMs depended on the initial position of the eye in that the elicited SEMs appeared to be converging toward a common point, or "orbital goal", and the SEM velocity diminished as the gaze neared that goal.2+ Both our SEM after anticipatory saccades and microstimulated SEM in the monkey slowed as the initial position was brought closer to the inferred orbital goal. This similarity suggests that the goal-directed SEM sites in the monkey might be part of a mechanism for predictive pursuit.
Variation of the resting potential caused by eye movements was analyzed by applying a battery model to the eyeball. A formula that gives the potential between the inner canthus and the outer canthus of the eye was derived on the basis of the electric theory in electromagnetics, on the assumption that the eyeball was floating in a homogeneous conductor. The variations of the resting potentials were represented using the distance from the center of the eyeball to the potential detecting position and the deflection angle of the position with respect to the optical axis of the eyeball. To verify the validity of the formula, the variation of the resting potential caused by the various amplitudes of bilaterally symmetrical eye movements were measured. The calculated results were found to be in good agreement with the experimental ones.