Human visuo-vestibular interaction as a basis for quantitative clinical diagnostics.

Visuo-vestibular interaction during randomized and sinusoidal head oscillations (0.5-5.0 Hz) was measured by power spectral analysis. It was shown that visual eye movement programmes can adjust the vestibulo-ocular reflex (VOR) gain at frequencies exceeding the dynamic range of visual tracking: above 3 Hz, gains exceeded unity during attempted fixation of a target moving with the subject whereas unity gains prevailed during fixation of an earth-fixed target. At low frequencies, fixation suppression was more efficient (-10 dB) when sinusoidal stimuli rather than randomized oscillations (-3 dB) were employed. Identical results were obtained when the fixation target moved with a total visual surround or against an earth-fixed visual background. Therefore, peripheral vision is normally not important for visual suppression of the VOR, which is dominated by foveal visual tracking at low frequencies.