Head-free gaze control in humans with chronic loss of vestibular function.

Healthy subjects use the vestibulo-ocular reflex (VOR) to stabilize gaze. Labyrinthine-defective humans without VOR still are, to some extent, able to maintain gaze stability during active eye-head movements. Here it is investigated whether this stabilization is due to anticipatory mechanisms or proprioceptive feedback. The head inertia was increased in humans who have undergone bilateral vestibulectomy (vestibular subjects) and in healthy controls during large gaze shifts. This leads to head oscillations in both groups. Whereas controls compensate for head oscillations and maintain gaze stability, vestibular subjects display gaze oscillations along with head oscillations. This indicates that vestibular subjects mainly use learned, anticipatory mechanisms, and not proprioception, to stabilize gaze.