Use of active head movements for computerized vestibular testing.

The vestibulo-ocular reflex (VOR) is seldom tested above 2 Hz, in spite of the higher-frequency components that stimulate it during natural head movements. We tested the horizontal VOR in ten normal subjects during 18 s of active, side-to-side head motion over a frequency range from 2 to 6 Hz. Audible clicks were used as a linearly increasing frequency cue. Head velocity was monitored. The two experimental conditions were head movement while fixating a stationary wall-mounted target in dim light, and head movement in darkness with an imagined stationary target. Computed gain and phase results of the two test conditions were not significantly different, due to inactivation of the smooth pursuit system above 2 Hz. We conclude that higher-frequency VOR responses can be tested in the light by a brief, low-cost test, which does not require expensive rotating machinery.