Effects of Centrifugal Force upon Spatial Orientation and Eye Position in Human Subjects.

Linear acceleration (CF) caused by centrifugal force results in ocular deviation and change in spatial orientation. Thirteen healthy human subjects and one labyrinthine defective (LD) subject were exposed to CF to examine the change in spatial orientation and eye position. CF was applied by rotating the subject at a 90 cm off-center position (eccentric rotation). Constant angular velocities of 80, 100, 120 and 140 deg/sec depicted CF of 0.18 to 0.55 G. CF was introduced in two chair positions as it affects along the inter-aural (X) or naso-occipital (Y) axes. Subjects were asked to adjust an LED bar to a perpendicular position while the chair was rotated in the darked room. Judgement for visual vertical was very accurate when the chair was stationary (with deviation of the bar within 1.1 degrees). Under CF along the X-axis, judgement for subjective perpendicular changed (i.e., toward the center of rotation). Amplitude of the tilting angle significantly increased as a function of CF (ANOVA, p<0.05). However, no significant change in bar deviation was found in one LD subject during the rotation. Also, CF along the Yaxis did not cause any significant deviation of the bar in healthy volunteers. Eye movement during eccentric rotation was analyzed by using an infrared video camera and computer analyzing system. Torsional eye deviations with amplitudes of 0.1 to 1.5 degrees were detected under CF along the X-axis. Under CF along the Y-axis, upward eye deviations with amplitudes of 1.6 to 3.2 degrees were detected. As the amplitude of eye deviation was very small in both conditions, it is assumed that the gain of otolithocular reflex had only a small gain. The linear acceleration acting upon the head had a larger influence upon spatial orientation than upon the oculomotor system.