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The Vintage Space video Eleven Deaf Men Helped NASA Leave Earth describes a number of different NASA experiments done on human subjects who had damaged vestibular systems due to childhood illness.

The experiments described would have been a horrible experience for those with functioning semicircular canals (e.g. living in a room with spinning walls for eleven days, boat ride on choppy seas so bad most control subjects vomited) but the subjects were "completely immune to motion sickness".

During a crewed spaceflight mission from launch to landing, are there any useful functions served by the vestibular system? Do astronauts use this sense in any way? Does it have any redeeming qualities during a mission?

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    $\begingroup$ I bet the sense of acceleration the vestibular system can provide helps astronauts move in zero g. $\endgroup$
    – CourageousPotato
    May 17, 2019 at 8:12
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    $\begingroup$ It was useful flying the shuttle down. $\endgroup$
    – Organic Marble
    May 17, 2019 at 11:33
  • $\begingroup$ @OrganicMarble I'm looking forward to hearing more about that! It's important to remember that being strapped in a capsule is not the only way people launched and landed. $\endgroup$
    – uhoh
    May 17, 2019 at 11:36
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    $\begingroup$ @uhoh I'm guessing that with the shuttle, it's valuable to feel the acceleration you're inducing as you move the controls. I've flown a plane once, and feeling the acceleration was a natural part of the piloting process. A related question would be to investigate whether anyone has piloted an aircraft with a damaged vestibular system. It's an interesting question. I would guess that it's an important part of moving in 0-g. However, as people with a damaged vestibular system have adapted to Earth, I'm sure that they could adapt to 0-g as well and maneuver themselves without too much challenge. $\endgroup$
    – user31448
    May 17, 2019 at 15:30
  • $\begingroup$ @RangaRutiserSundar these are interesting points! There is an Aviation SE site, perhaps it's been asked there already. $\endgroup$
    – uhoh
    May 17, 2019 at 15:35

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During the first 3-4 days of spaceflight the vestibular system is essentially useless as the brain becomes confused by sensations in the inner ear that do not match what is seen with the eyes. For most astronauts this results in varying levels of space adaptation syndrome (space sickness) as well as spatial disorientation and other impairments. This includes the sensation of phantom movements as the fluids float around inside the inner ear. Other symptoms such as a sustained sensation of tilting can be experienced. Sudden head movements are especially problematic and astronauts are encouraged to keep this to a minimum.

However within a few days the brain begins to adapt to the new environment and essentially remaps itself to the new inputs caused by the changed behavior of the fluids in the absence of gravity, and the symptoms largely disappear, although not completely, and the vestibular system becomes useful again. There are even physical changes that begin to occur such as an increased number of the hair cells that are used as receptors, as discussed in this National Library of Medicine article Challenges to the Vestibular System in Space: How the Brain Responds and Adapts to Microgravity.

Upon return to Earth the brain has to go through the remapping process again as it readapts to the gravity environment.

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  • $\begingroup$ Small point, but the paper quoted in the answer does not describe “increased number of the hair cells”. Instead, it describes “increases in the number of …hair cell synapses”. That is, the neural connections with other nerve cells. This is analogous to a change in “software” rather than “hardware”. $\endgroup$
    – Woody
    Aug 27 at 16:19
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Answer: The vestibular system is useful in spaceflight for maintaining visual fixation. Without a vestibular system, vision would be degraded when the head is moving in relation to the object of regard.

The eyes move with the head. Vision is blurred during head movement unless there are compensatory eye movements. The vestibular system's job is to drive those compensatory eye movements.

The vestibular system senses rotational movements of the head and compensates for them. The output from the vestibular system connects with the oculomotor nerve (the nerve which controls the majority of eye movements). This is called the Vestibulo-ocular Reflex (VOR). It is responsible for maintaining visual fixation during head movements.

To illustrate the effect of VOR, hold a finger in front of your face and wiggle it side-to-side rapidly. Your eyes are not able to track the finger’s movement, so it is seen as a blur. Now hold your finger still, but rotate your head rapidly side to side while fixating on your finger. Fixation is much better (the image is much clearer) than when wiggling your finger.

If both finger wiggling and head shaking are each done at the same frequency (count out loud as you do each), it is clear how much better fixation is with VOR during the head shake.

In a space mission, the VOR will assist in maintaining visual fixation during both voluntary head movements and involuntary head movement i.e.: shaking of the spacecraft.

It would be interesting to test adult subjects with compromised vestibular systems. The subjects described in the OP would not be suitable for this experiment since they all lost their vestibular function in childhood. Developing brains have a greater capacity for plasticity than adult brains. This plasticity would confound the results.

https://en.wikipedia.org/wiki/Vestibular_nuclei https://en.wikipedia.org/wiki/Vestibular_system https://en.wikipedia.org/wiki/Vestibulo%E2%80%93ocular_reflex

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  • $\begingroup$ I recently had an inner-ear infection and the ear doctor diagnosed me using my eyes. He asked me to look at a light and watched my eyes repeatedly drift steadily to one side then return. Could have been another problem (e.g. "loose stone") but was told to give it a week and come back if it's still a problem. $\endgroup$
    – uhoh
    Aug 26 at 2:39
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    $\begingroup$ Interestingly on the flip side it's relatively easy to stand on one leg with your eyes open, but much more difficult with your eyes closed when you are relying solely on the vestibular system for balance. Similar to your example it demonstrates how both are needed. $\endgroup$
    – Steve Pemberton
    Aug 26 at 9:27
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    $\begingroup$ Just to point out for those who may not have noticed, you were the first person to answer this four year old question. Well done. $\endgroup$
    – Steve Pemberton
    Aug 26 at 15:11

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