Modeling Sensory Conflict and Motion Sickness in Artificial Gravity
- Paper number
IAC-05-A1.3.08
- Author
Mr. Laurence R. Young, Massachussets Institute of Technology (MIT), United States
- Coauthor
Dr. Thomas Jarchow, Massachussets Institute of Technology (MIT), United States
- Coauthor
Mr. Paul Z. Elias, Massachussets Institute of Technology (MIT), United States
- Year
2005
- Abstract
Artificial Gravity implemented via short-radius centrifugation is a promising countermeasure against the debilitating physiological effects of weightlessness. However, a significant practical challenge arises from the unusual stimuli applied to the vestibular organs as a result of head movements made in a rotating environment. For a head turn on a centrifuge, the absolute angular acceleration of the head is the sum of three vectors: the carrying angular acceleration of the centrifuge, the angular acceleration of the head relative to the centrifuge, and an additional term commonly referred to as the Coriolis Cross-Coupled Acceleration, which is equal to the cross product of the relative angular velocity of the head and the angular velocity of the centrifuge. The stimulus to each semicircular canal consists of the absolute acceleration vector projected onto the canal’s rotation axis, with the Coriolis term being dominant. Such stimuli lead to undesired sensations of illusory motion, inappropriate vertical and torsional nystagmus, and varying levels of motion sickness. The MIT Man-Vehicle Laboratory studies adaptation to head movements in Artificial Gravity on a 2-meter radius centrifuge upon which subjects lie supine and rotate about a naso-occipital axis (earth-vertical). Experiments are generally conducted at a constant rotation rate of 23 rpm, corresponding to a radial acceleration of approximately 1 g at foot level. Given recent success at adapting individuals to head movements at 23 rpm over as little as 2 days, a goal was set to reach a similar level of adaptation at 30 rpm. However, with the discomfort levels observed in experiments at 23 rpm, the stimuli resulting from head turns at 30 rpm without prior adaptation at lower speeds would likely induce excessive nausea. To design an incremental adaptation protocol aimed at adapting subjects to head movements at 30 rpm, a model was used to describe the sensory conflict, motion sickness, and adaptation associated with head movements in Artificial Gravity. The model of sensory conflict was based upon differences between expected and actual sensory afference from the semicircular canals during head movements in a rotating environment. Afferent firing rates were determined using a transfer function developed by Borah and Young (1988) describing canal firing rates as a function of angular acceleration. An existing mathematical model (Oman, 1990) describing motion sickness onset and evolution as a function of sensory conflict was employed to make quantitative predictions in designing the adaptation protocol. However, since the Oman motion sickness model did not include a description of adaptation, we developed an adaptation parameter through analysis of past experimental results and incorporated it into the model. With the sensory conflict model providing the input to the modified motion sickness model, an experimental protocol was designed such that predicted adaptation over several days would eventually allow head movements at 30 rpm without excessive motion sickness. Execution of the experimental protocol and subsequent comparison between actual and predicted motion sickness results will enable evaluation of the model and potential improvements. Supported by the National Space Biomedical Research Institute under grant from NASA.
- Abstract document
- Manuscript document
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