Orientation of the Rotation-Axis Relative to Gravity: Its Influence on Nystagmus and the Sensation of Rotation

Subjective phenomena and nystagmus were compared under two conditions of rotation, one in which the axis of rotation was vertical, i.e., aligned with gravity, and one in which the rotation-axis was horizontal. When the axis of rotation was horizontal, normal subjects exhibited nystagmus and sensations of rotation for periods of three minutes (and longer); deceleration produced very brief post-rotational reactions. L-D subjects, men presumed to be without vestibular function, did not exhibit nystagmus or report sensations similar to those of normal subjects for either the vertical or horizontal axis of rotation. Because prolonged nystagmus occurred almost exclusively in normal subjects when the rotation axis was horizontal, it is concluded that vestibular function is a necessary condition for this response and that it may be dependent upon the continuous reorientation of the otolith system relative to gravity. The results emphasize the importance of increasing our range of experimental observations to check the accuracy of theoretical predictions.