Cyclovergence evoked by up-down acceleration along longitudinal axis in humans.

We present results of a study of torsional eye movements evoked by earth-vertical accelerations along the subject's longitudinal axis. The earth-vertical stimulus leads to a gravito-inertial acceleration vector that changes magnitude but not direction. It can therefore be viewed as a dynamic change of the gravity level. Up-down oscillations induced relatively symmetric cyclovergence (0.6-2.2 degrees peak-to-peak). Eyes intorted/extorted for higher/lower effective gravity. The phase of this modulation was small relative to chair acceleration. We contrast this behaviour to the dynamics of cycloversion in response to interaural acceleration, which shows a considerably larger phase lag. This strikingly different dynamics suggest a different processing of otolith signals during interaural and longitudinal stimulation.