Donohew BE, Griffin MJ. Motion sickness with combined lateral and roll oscillation: effect of percentage compensation. Aviat Space Environ Med 2010; 81:22–9. Background: Both lateral acceleration and roll through the force of gravity produce lateral forces. On a tilting-train the tilt offsets lateral acceleration so as to improve the physical comfort of passengers, but motion sickness is believed to increase as the lateral force is reduced by increased roll (i.e., as the percentage roll compensation is increased). Objectives: We investigated how motion sickness caused by combined lateral acceleration and roll displacement depended on the percentage compensation. Method: There were 8 groups of 20 subjects who were exposed for up to 30 min to various conditions of combined lateral and roll oscillation: 3 groups of 20 subjects experienced 0.2 Hz oscillation with 1 of 3 compensations (0, 50, or 100%) and 5 groups of 20 subjects experienced 0.1 Hz oscillation with 1 of 5 compensations (0, 25, 50, 75, or 100%). With both frequencies of sinusoidal oscillation, the peak Earth-lateral acceleration was 1.26 m · s⁻². Subjects provided ratings of their motion sickness symptoms at 1-min intervals. Results: The percentage compensation had significant effects on motion sickness. With 0.2 Hz oscillation, 50% roll-compensation of lateral oscillation produced less motion sickness than uncompensated lateral oscillation, and less motion sickness than 100% roll-compensated lateral oscillation. With 0.1 Hz oscillation, 25% roll-compensation of lateral oscillation produced significantly less motion sickness than either 75% or 100% roll-compensated lateral oscillation. Conclusions: Motion sickness caused by combined lateral and roll oscillation is dependent on the percentage compensation and cannot be predicted by models based on only lateral oscillation or only roll oscillation.