The SICKNESS project (1996 – present)

Acronym: SICKNESS
Name: Postural stability and motion sickness
Type: Collaborative project
Funds: National Institute of Health - French Institut Universitaire de France
UM1 key researcher: Benoît Bardy
Collaborator (PI): Tom Stoffregen (Univ. Minnesota, USA)

SICKNESS is a theoretical and experimental project aiming at identifying the cause of motion sickness in standing and seating persons.

Theory:

Theories of motion sickness etiology have typically been based on the concept of sensory conflict. The essential idea of this approach is that motion sickness situations are characterized by patterns of perceptual stimulation that differ from patterns expected on the basis of past experience. In this project we evaluate an alternative theory of motion sickness etiology, the postural instability theory.

The postural instability theory (Riccio & Stoffregen, 1991) is not based on the concept of sensory conflict but, rather, on relations between perception and the control of action. This approach considers the behavior of the individual as fundamental in motion sickness etiology. The postural instability theory of motion sickness predicts that motion sickness will be preceded and predicted by instabilities in control of the posture. The theory is being tested.

Past experiments:

The incidence of motion sickness is strongly related to the frequency of imposed periodic motion. Motion sickness is found almost exclusively when imposed periodic motion includes frequencies from 0.08 to 0.4Hz. Vibration in this frequency range is characteristic of nauseogenic vehicles, such as ships, trains, and aircraft. Optical motion at these frequencies is sufficient to induce motion sickness in standing participants, even when the amplitude of oscillations is so small that many participants are not aware that anything is moving.

These effects are peculiar because ordinary standing body sway is characterized by low amplitude oscillation between 0.1 and 0.3Hz. We are not sickened by our own postural motion, but we can be sickened by a simulation of the optical consequences of body sway that is accurate in terms of frequency and amplitude. Why should this be so?

We have hypothesized that the imposed optical simulation of body sway interacts with actual sway to produce unstable control of stance. Our hypothesis suggests that unstable control of posture might be observed in persons who experience motion sickness while exposed to an accurate simulation of the optical consequences of body sway. The postural instability theory of motion sickness predicts that postural instability should precede the onset of motion sickness symptoms. This prediction has been confirmed in the context of stance (Smart, Stoffregen, & Bardy, 2002). During exposure to imposed optical flow, participants who later became motion sick exhibited increases in postural sway. Increases were observed in the variability, velocity, and range of postural motion.

Vertical velocity for representative participants during baseline (left: simple sine à 0.2 Hz; right: sum-of-sine) motion of the moving room (eyes open). Participants who later became sick are on the right (extracted from Smart et al., 2002).

Current experiments:

Based on these and other results, our current experiments (Faugloire et al., 2006; Bonnet et al., 2006) test two complementary aspects of the postural instability theory.

1. Passive restraint: If motion sickness is related to unstable control of posture, then motion sickness should occur only in the context of active attempts to control posture.  Under full passive restraint (e.g., when strapped down) a person cannot move.  It should be impossible for such persons to become unstable, and so the postural instability theory of motion sickness predicts that they should be immune to motion sickness. The prediction is now being tested (Faugloire et al., 2006).
2. Center of pressure signatures: The postural instability theory does not predict that instability would be found in or limited to any specific parameter of postural motion. Thus, it is important to look for signatures of instability in a variety of parameters of postural motion. In Bonnet et al. (2006), we examined the signatures of instabilities preceding motion sickness in the non linear dynamics of centre of pressure trajectories (DFA).

Key references (downloadable version in page Vitae):

1. Smart, L.J., Stoffregen, T.A., & Bardy, B.G. (2002). Visually induced motion sickness predicted by postural instability. Human Factors, 44, 451-465.
2. Bonnet, C. T., Faugloire, E. M., Riley, M. A., Bardy, B. G., & Stoffregen, T. A. (2006). Motion sickness preceded by unstable kinematics of the center of pressure. Human Movement Science, 25, 800-820.
3. Faugloire, E., Bonnet, C., Riley, M. T., Bardy, B. G., Stoffregen, T. A. (2007). Motion sickness, body movement, and claustrophobia during passive restraint. Experimental Brain Research, 177, 520-532.
4. Bonnet, C., Faugloire, E., Riley, M., Bardy, B. G., & Stoffregen, T. A. (2008). Self-induced motion sickness and body movement during passive restraint. Ecological Psychology, 20, 121-145.