Motion sickness with Earth-horizontal translational and rotational oscillation presented in isolation and in combination

Joseph, Judith Anoushka (2008) Motion sickness with Earth-horizontal translational and rotational oscillation presented in isolation and in combination. University of Southampton, Institute of Sound and Vibration Research, Doctoral Thesis, 200pp.

Record type: Thesis (Doctoral)

Abstract

Low-frequency Earth-horizontal translational and rotational oscillations can cause motion
sickness in transport. Previous studies have found that motion sickness depends on the
frequency, magnitude, direction and duration of the motion, however, knowledge of the
mechanisms of motion sickness is far from complete. The concept of sensory conflict – that
motion sickness arises because of a conflict between sensed and expected sensory
information is central to theories of motion sickness, but little is known about how the physical
characteristics of motion influence sensed and expected sensory signals. The aim of this
research was to advance understanding of the effect on motion sickness of factors which may
influence sensed and expected vestibular signals during exposure to low-frequency
translational and/or rotational oscillation.
The first experiment investigated whether motion sickness depends on the phase between
combined lateral acceleration and roll oscillation at 0.2 Hz. The roll oscillation had one of four
phases relative to the lateral acceleration: 0° delay, 14.5° delay, 29° delay, and 29° advance.
Sickness decreased as the delay in the roll motion increased; less sickness occurred with a
phase advance than a phase delay, suggesting that motion sickness cannot be predicted from
the acceleration in the plane of the seat.
The second experiment investigated how motion sickness varies between four 60-minute
exposures of 0.1 Hz combined lateral and roll oscillation which involved different combinations
of a high and low magnitude motion: LLLL, HHHH, LHHL and HLHL. The high magnitude
motion produced greater sickness than the low magnitude motion. For the two variable motion
conditions, there was no significant difference in accumulated illness ratings when the motion
sickness dose values were the same.
In the third experiment, 0.2 Hz roll and pitch oscillation were studied at three displacements:
±1.83° ±3.66° or ±7.32°. A trend for motion sickness to increase with increasing displacement
was observed; similar sickness was caused by roll and pitch oscillation at each magnitude.
In the fourth experiment, subject head displacement was measured during 0.2 Hz fore-and-aft
oscillation with and without a backrest at three magnitudes: 0.22, 0.44, and 0.89 ms-2 r.m.s.
Illness increased systematically with increasing magnitude of oscillation with a backrest, but less
systematically without a backrest, suggesting an interaction between the effect of motion
magnitude and the influence of a backrest. There were no significant differences in illness with
or without a backrest at any of the magnitudes studied. Between subjects, there was little
evidence to suggest that greater fore-and-aft and pitch displacement of the head was
associated with an increase in motion sickness.
Combined findings from the third and fourth experiments suggest that 0.2 Hz fore-and-aft
oscillation causes greater sickness than 0.2 Hz pitch oscillation at each of the three magnitudes
studied (assuming that pitch motion can be represented by the gravitational component, gSin?).
A motion sickness model is proposed showing how the factors investigated in this thesis affect
the sensed and expected semi-circular canal signals which are assumed to be involved in the
causation of motion sickness. The model predicts how sensed and expected signals vary
according to the phase between motions, the magnitude, direction and duration of motion, the
type of motion and the postural support given to subjects. Explanations of how the model
predicts motion sickness based on the findings of this study and previous studies are discussed.