Discomfort from sinusoidal oscillation in the roll and lateral axes at frequencies between 0.2 and 1.6 Hz.

Discomfort caused by low frequency lateral and roll oscillations is often predicted from lateral acceleration in the plane of the seat, irrespective of whether it comes from horizontal motion or a component of gravity arising from roll. This study investigated discomfort from lateral and roll oscillation and whether acceleration in the plane of a seat predicts discomfort. Twelve subjects, sitting with and without backrest, used magnitude estimation to judge sinusoidal oscillations in the roll and lateral axes at ten frequencies between 0.2 and 1.6 Hz at magnitudes between 0.063 and 0.63 m s(-2) root mean square. The rate of growth of vibration discomfort with increasing magnitude reduced with increasing frequency, so the frequency-dependence of discomfort varied with magnitude. Acceleration in the plane of the seat predicted discomfort from both lateral and roll oscillation at frequencies less than 0.4 Hz. At higher frequencies, acceleration produced by roll oscillation resulted in greater discomfort than the same acceleration produced by lateral oscillation. At frequencies greater than 0.4 Hz, a full height backrest increased discomfort with both lateral and roll oscillation. The prediction of discomfort caused by low frequency lateral and roll oscillation requires that both components are measured and assessed according to their separate effects.