Eye-head Coordination in Labyrinthine-defective Human Beings

(1) Eye-head coordination was studied in three human beings with absent labyrinthine function. Each subject adopted a unique pattern of adaptive responses to achieve optimal gaze stability. (2) One subject used saccades (even in darkness) to help stabilize gaze. In addition, during rotation of the body with the head stationary in darkness, he made slow and quick phases of nystagmus in the same direction. This subject apparently used quick phases to help stabilize gaze rather than to redirect the center of visual attention. (3) One subject, to help prevent gaze overshoot, showed a decrease in the saccadic amplitude-retinal error relationship selectively during active combined eye-head movements. (4) One subject showed a significant amount of preprogramming of compensatory slow phases independent of actual head motion. (5) In all subjects, the passively induced cervico-ocular reflex was moderately potentiated, accounting for about 25% of compensation for head motion during active target seeking. (6) In all subjects, 'effort of spatial localization', as shown by imagining targets in total darkness, increased the velocity of compensatory slow phases to near that of head movements during both active and passively induced head rotations. (7) In all subjects, gaze stability was enhanced during tracking of targets jumping in a predictable fashion. (8) The choice of strategies used by each subject may depend, in part, upon the latency of the cervico-ocular reflex during active head movements.