Extent of reaction capacity of the vestibulo-ocular reflex.

On theoretical grounds, a high capacity of the vestibulo-ocular reflex, compensating for head velocities above 300 degrees/s, is assumed. However, in man the maximum eye speed, induced by solely vestibular stimuli, is only 100 degrees/s. With the usual clinical tests is seems impossible to get a sufficient strength of stimulus that would correspond to a strong physiological stimulus. With a systematic investigation with fistula symptoms finally a patient was found with an ideal mechanism of release of the fistula symptom. The maximum eye speed of the compensatory phase was 315 degrees/s. In this case, the vestibular phase was quicker than the so-called rapid phase. This now proven high reaction capacity constitutes the "missing link" between the hypothetical high capacity of the systems concept and the until now measured, only limited reactions after solely vestibular stimulation. For most physiological stimuli, i.e., quick head movements, the system can act as a simple reflex organ, being a velocity transducer with linear function thus successfully maintaining ocular fixation.