When a stationary human observer watches a moving visual stimulus, he or she may experience postural disturbance and illusion of self-motion (vection). While studies of postural disturbance of viewers watching scene oscillations of different frequencies in roll direction has led to important discoveries on the possible cause of motion sickness (Duh et al., 2004), similar studies with scene oscillations in fore-and-aft direction are not found. This thesis examines the frequency response of postural disturbance and vection when viewing visual stimulus oscillating in roll direction and in fore-and-aft direction. The range of frequency investigated is from 0.05 to 0.8 Hz. Participants watching oscillating stimuli in both direction exhibited significantly higher postural disturbance and vect...[ Read more ]

When a stationary human observer watches a moving visual stimulus, he or she may experience postural disturbance and illusion of self-motion (vection). While studies of postural disturbance of viewers watching scene oscillations of different frequencies in roll direction has led to important discoveries on the possible cause of motion sickness (Duh et al., 2004), similar studies with scene oscillations in fore-and-aft direction are not found. This thesis examines the frequency response of postural disturbance and vection when viewing visual stimulus oscillating in roll direction and in fore-and-aft direction. The range of frequency investigated is from 0.05 to 0.8 Hz. Participants watching oscillating stimuli in both direction exhibited significantly higher postural disturbance and vection than watching stationary stimuli. Both the postural disturbance and vection reduce significantly with increasing scene oscillating frequency. Data obtained have been integrated with Duh et al. (2004)’s result to provide new insight in the possible cause of motion sickness. So far, both the author and Duh had manipulated the scene oscillation by varying oscillation amplitudes at a constant peak velocity of 70°/sec. A second study has been conducted to examine the effect of peak roll oscillation velocity on postural disturbance and vection. Frequency of visual stimulus oscillation was held constant at 0.05 Hz. Among the four peak velocities being tested (35, 70, 100 and 140°/sec), it was found that postural disturbance and vection at 35°/sec condition are significantly lower than other velocity conditions. Implications of the second study on Duh et al. (2004)’s work are discussed.