Influence of voluntary ocular deviation on vestibular nystagmus.

We examined the influence of voluntary gaze deviation on per-rotary vestibular nystagmus during trapezoidal velocity profiles. Gaze deviation in the direction of the fast-phase component of nystagmus significantly increased slow-phase amplitude, fast-phase amplitude and slow-phase velocity; gaze deviation in the direction of the slow phase marginally decreased these three properties. Schlagfeld deviation and beat frequency were unaffected by per-rotary ocular deviation in either direction. The observed changes in per-rotary eye movements are consistent with post-rotary observations first described by Alexander which later became known as "Alexander's Law".