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Human Vestibular Function (M131)
Research Area:
Species Studied
Scientific Name: Homo sapiens Species: Human

Neuroscientists agree that space motion sickness (SMS) is one of the most clinically significant problems that astronauts encounter during the first few days of space flight. The occurrence of SMS in one or more crewmembers can disrupt important activities during the early, critical stages of a mission. The onset of SMS is rapid and symptoms generally appear within an hour after exposure to microgravity. Typical symptoms of SMS include malaise, loss of appetite, lack of initiative, and irritability. If SMS reaches advanced stages, symptoms worsen and may include nausea, vomiting, headache, and impaired concentration. Considering the symptoms and the potential for lost crew time, it is easy to understand why researchers are investigating the causes of SMS and potential treatments.

Numerous hypotheses attempt to explain the physiologic causes of SMS. The majority of these hypotheses focus on the vestibular system and how it responds to microgravity. The vestibular system consists of two identical vestibular organs located on either side of the head in the inner ear. It functions to maintain the body's balance by detecting the position and motion of the head. Each organ is made up of three semicircular canals that detect angular accelerations in three different planes in space and two otolithic organs which detect linear accelerations. The otolithic organs depend on gravitational forces to function properly; therefore, they are especially sensitive to microgravity conditions. The semicircular canals and the otolithic organs work in conjunction with visual inputs to send signals to the brain, which then activates the appropriate muscles to keep the body balanced. Exposure to microgravity affects the relationship between the vestibular signals and visual inputs and thus causes a sensory conflict in the brain. The sensory conflict occurs because the visual inputs from the eyes do not agree with the signals from the vestibular system. A good example of this occurs when a crewmember is floating weightless and upright in reference to the Skylab's floor, but in reality he may be completely upside down due to microgravity. Accordingly, visual inputs in this situation would indicate the correct "up" and "down" orientation but the vestibular organs would not sense the correct orientation because they rely on gravity to function properly. Researchers believe that this sensory conflict is the underlying mechanism responsible for SMS, illusions of motion and spatial-orientation disturbances.

Skylab scientists noted that the incidence of SMS increased on the Apollo missions as compared to the Mercury and Gemini missions. They attributed this to the larger size of the capsule which allowed for greater mobility of the crew. In addition, it was known that SMS is caused by a combination of microgravity and head or whole-body movements that produce changes in one's spatial orientation. These findings prompted researchers to investigate human vestibular function on Skylab missions since these missions would involve a great deal of activity in a large workshop for extended periods of time. Thus, the objectives of Experiment M131 were to (1) establish the validity of specific behavioral/physiological responses influenced by vestibular activity under 1-g and microgravity conditions, (2) determine man's adaptability to unusual vestibular conditions and to predict the habitability of future spacecraft environments, and (3) investigate man's ability to accurately judge spatial coordinates without the aid of visual inputs and while under the influence of microgravity.

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'Miller EF II, Graybiel A. Altered susceptibility to motion sickness as a function of sublevel gravity. Space Life Sciences. 1973; 4:295-306.[]

Graybiel A, Miller EF II, Homick JL. Experiment M131. Human Vestibular Function. In: Johnson RS, Dietlein L, eds. Biomedical Results from Skylab. Washington, DC: NASA Headquarters. 1977:175-81. NASA SP-377. [NTRS]

Graybiel A, Miller EF II, Homick JL. Experiment M131. Human Vestibular Function. In: Johnston RS, Dietlein LF, editors. Proceedings of the Skylab Life Sciences Symposium; 1974 Aug 27-29; National Aeronautics and Space Administration, Johnson Space Center; 1974; 373-86. Report No: JSC-09275, Report No: TM X-58154. [NTRS]

Graybiel A, Miller EF, and Homick JL. Individual differences in susceptibility to motion sickness among six Skylab astronauts. Acta Astronautica. 1975. Jan-Feb; 2(1-2):155-74. []

Miller EF II, Graybiel A. A provocative test for grading susceptibility to motion sickness yielding a singular numerical score. Acta Otolaryngol 1970; 274:1-20.[]

Miller EF II, Graybiel A. Experiment M-131. Human Vestibular Function. Aerospace Med 1973. June; 44:593-608.[]

Vestibular function tests
Head movements

Data Information
Data Availability
Archive is complete. Data sets are not publicly available but can be requested.
Data Sets+ Request data

Head movement characteristics
Otolith function
Semicircular function
Severity of malaise
Spatial orientation recognition: external reference
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
Skylab 2 05/25/1973 06/22/1973 28 days
Skylab 3 07/28/1973 09/25/1973 59.5 days
Skylab 4 11/16/1973 02/08/1974 84 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Eric Gallagher
Institutional Support
National Aeronautics and Space Administration (NASA)
Hardware Items