Motion sickness from combined lateral and roll oscillation: effect of varying phase relationships.

BACKGROUND

Previous studies have investigated motion sickness caused by combined lateral and roll oscillation occurring in phase with each other. In tilting trains there can be a phase difference between the two motions.

HYPOTHESIS: It was hypothesized that sickness caused by combined lateral and roll oscillation would depend on the phase between the lateral acceleration and the roll displacement.

METHOD: At intervals of at least 1 wk, 20 subjects were seated in a cabin and exposed to four 30-min exposures of combined 0.2 Hz sinusoidal lateral acceleration (+/- 1.26 ms(-2)) and 0.2 Hz roll displacement (+/- 7.32 degrees). The roll oscillation had one of four phases relative to the lateral oscillation: 1) 0 degrees delay (giving 100% compensation of the lateral acceleration); 2) 14.5 degrees delay (75% compensation); 3) 29 degrees delay (50% compensation); and 4) 29 degrees advance (50% compensation). Subjects gave ratings of sickness at 1-min intervals.

RESULTS

Sickness was greatest with no delay (100% compensation). Increasing the delay to 14.5 degrees (75% compensation) and to 29 degrees (50% compensation) decreased sickness. Less sickness occurred when the roll displacement led the lateral acceleration by 29 degrees (phase advance) than when the roll displacement followed the lateral acceleration by 29 degrees (phase delay).

CONCLUSIONS

With combined lateral and roll oscillation, sickness depends on the phase between the two motions. Increasing the delay in the roll motion reduces sickness, but also reduces the compensation. There is less sickness when the roll displacement leads the lateral acceleration than when the roll displacement lags the lateral acceleration.