The effect of altering the head's mechanics on gaze shift accuracy in humans /
Vasileios Kokkinos · eScholarship@McGill (McGill) · 2006
A novel methodology for investigating the performance of the eye-head coordination system in humans is proposed. The objective is to alter the head's mechanics by applying torque loads during gaze shifts. A servo-motor, connected to the subject's head through a "motor shaft-to-dental bite" arrangement, is applying brief torque pulses in order to both aid and resist the head's movement, thus increasing and reducing respectively the head's velocity. The subjects perform a simple visual task to guide their gaze shifts in the dark, that is, after fixating on a standard point in space, a briefly flashed target will indicate the amplitude of the required gaze movement. Three targets appear in the horizontal plane within, at the limits of, and beyond the human oculomotor range (40°, 55°, and 70° respectively) in order to cover a significant range within which the head's contribution to the gaze coordinated movement is indispensable. The main question, the proposed methodology aims to answer, regards the effect of the torque loads on gaze shift accuracy. Two (2) subjects were tested under the above-mentioned conditions. Their accuracy was not significantly affected, although both head velocity and gaze duration were considerably altered by the torque loads. The results support the existence of a feedback control mechanism in the eye-head coordination system that keeps track of the on-going movement and adjusts the movement's kinematics on-line accordingly.