Three‐Dimensional Eye Velocity Measurement following Postrotational Tilt in the Monkey a

Angular head accelerations are known to elicit reflexive movements of the eye called the angular vestibuloocular reflex (VOR). If an upright subject is rotated about an earth-vertical axis a t a constant angular velocity and then decelerated after some time, horizontal postrotatory nystagmus follows. Recently a number of studies (monkey;' human;* cat3) have demonstrated the existence of an exponentially decaying vertical nystagmus as well as horizontal nystagmus following rotation about a nonvertical axis. Each of these studies indicated that the vertical response, combined with the horizontal nystagmus, tended t o align the compensatory motion of the pupil with earth horizontal. Two earlier human studies reported the presence of a vertical nystagmus during cent r i fuga t i~n .~ .~ A later set of studies repeated this paradigm with monkeys and measured the extent of an axis transformation that moved the axis of eye rotation toward alignment with gravitoinertial Monkey studies have also demonstrated a shift in the axis of the optokinetic after-nystagmus ( O W ) response when the rotational axis of the stimuli did not align with gravity.8 While the authors acknowledged the presence of cross-talk between the channels and could not quantitatively show the extent to which the response deviated from yaw, these data showed the presence of position dependent vertical or torsional responses which shifted the axis of the eye movement responses toward a spatial-vertical axis. We have measured all three dimensions of eye rotation during and following vestibular stimulation. We also have developed and implemented a n algorithm that allows us to minimize the cross-talk between the eye measurement channels and permits us to evaluate the change in the axis of eye rotation quantitatively.