Dynamic characteristics of the otolithic oculomotor system.

Vertical eye tracking test, up-down test, and running test in the dark and light were carried out to obtain Bode plots of transfer function of the opto-oculomotor, otolithic oculomotor, and opto-otolithic oculomotor systems. 1. The gain and phase of the opto-oculomotor system obtained from the vertical eye tracking test were flat in a frequency range of 0.3 to 1.0 Hz. 2. During the up-down test in the dark, the gain of the otolithic oculomotor system linearly increased at the rate of 20 dB/decade with an increase of frequency from 0.7 to 5 Hz. 3. During the up-down test in the light, the gain and phase were flat in a frequency range of 0.3 to 2.5 Hz. 4. The transfer function calculated with vertical head acceleration as input and vertical eye movement as output in the running test in the dark was similar to that in the light. The gain linearly decreased at the rate of 40 dB/decade with increase of frequency from 0.3 to 3.0 Hz. During running, eye displacement is almost in proportion to the head displacement in both dark and light. In daily, active movement such as running, eye movement proportional to head displacement appears without collaborative action of the opto-oculomotor system. 5. All five patients with bilateral loss of labyrinthine excitability exhibited a similar opto-oculomotor response to that of normal subjects. Three of the five patients did not show any eye movement corresponding to head movement in the up-down test in the dark. However, two patients showed a periodic eye movement in the same test, indicating dispersion of the gain and phase values. 6. These patients exhibited a rhythmic eye movement corresponding to head movement in the running test in the dark and light. However, values of gain and phase obtained in both tests were cultured. The variations in gain obtained from the running test in the light were observed in frequency ranges above and below 1 Hz.