Frequency effect of 0.35-1.0 Hz horizontal translational oscillation on motion sickness and the somatogravic illusion.

BACKGROUND

Low frequency translational oscillation can provoke motion sickness in land vehicles, ships and aircraft.

HYPOTHESIS

Nauseogenicity should decrease towards the higher frequencies.

METHODS

Some 12 subjects were exposed to horizontal sinusoidal motion (3.6 m.s-2 peak) at four different frequencies 0.35, 0.50, 0.70, and 1.00 Hz, at 1-week intervals, latin square order. Subjects were seated in the upright position; motion was through the head-body X-axis. Motion was stopped (motion endpoint) at moderate nausea or after 30 min.

RESULTS

The proportion of subjects experiencing moderate nausea decreased towards the higher frequency: 9/12 at 0.35 Hz, 3/12 at 0.50 Hz, 0/12 at 0.70 Hz, and 2/12 at 1.00 Hz. The mean time to motion endpoint increased significantly (p < 0.001) towards the higher frequency: 17.4 min 0.35 Hz; 26.0 min 0.50 Hz; 30 min 0.70 Hz; 28.3 min 1.00 Hz. Differences between frequencies were significant (0.001 < p < 0.05) except for 0.70 Hz to 1.00 Hz. At all frequencies tested, horizontal stimuli were more nauseogenic than predicted by mathematical models based on the frequency and intensity of vertical oscillation. Somatogravic illusion (SGI) was reported by 9/12 subjects (mean illusory tilt angles 15.6 degrees forward, 14.1 degrees back). SGI tended to diminish at the higher frequencies, but there was no relationship between SGI and motion sickness.

CONCLUSIONS

These results confirm previous findings (9), and furthermore indicate that horizontal X-axis translational oscillation has greatly reduced nauseogenic potential at frequencies greater than 0.5 Hz. A mathematical model is proposed to predict motion sickness intensity and incidence due to this stimulus, which may also be applicable to equivalent Y-axis motion.