Eye movements induced by gravitational force and by angular acceleration: their relationship.

Abstract

The relationship between putative 'canal' and 'otolith' function was studied by using both vertical axis and horizontal axis (barbecue spit) rotations. The vestibulo-ocular reflex (VOR) with eyes closed of 7 normal subjects during vertical axis rotation was characterized (0.02 to 1.67 Hz) using pseudorandom acceleration. Gain and phase points were calculated. The long time constant of the VOR was then estimated from the phase points using a simple linear systems model. The same subjects were also tested with eyes closed using earth horizontal axis rotations. Constant velocity rotation (60 degrees/sec) produced a periodic oscillation in the slope of the slow component of nystagmus known as the 'modulation component'. The amplitude of this component was averaged for clockwise and counterclockwise runs. For the 7 subjects, the amplitude of averaged modulation component correlated with the low-frequency phase values (r = 0.82 to 0.89) and VOR long time constant estimates (r = -0.95) obtained during vertical axis rotations. These data suggest a complementary relationship between responses to linear and to angular accelerations. Subjects having eye movement responses which are less sensitive to low-frequency angular acceleration also tend to have relatively greater responses to changing linear accelerations.