Explained by an Astronaut:
I ran across an interesting article in Forbes Magazine by Dr. Garret Reisman, former NASA astronaut. He was asked what it is like to return to earth after being in a gravity free environment on the international space station. I have a vague memory of this topic being discussed at one of the first vestibular courses I attended many moons ago. The course instructor asked, “Can anyone guess why the pilots sit on the tarmac for an hour before exiting the Space Shuttle?” After a few seconds of blank stares from those of us in the audience, he said. “It’s because they are throwing up or falling down, maybe both.” The instructor proceeded to explain that after the brain had a chance to adjust to a zero gravity environment in space, there was an adjustment period when re-entering a gravitational environment.
Dr. Reisman offers his perspective on this process:
“You see, your brain is remarkably adaptable. After just a few days in space it figures out that your inner ear is producing nothing but garbage signals and so the brain turns the gains of those signals way down in its Kalman filter and cranks up the gains on your visual sensors, the eyes. Then all is well, until you come back to Earth. Now you need your inner ear sensor again, but the brain is still filtering it out. Gradually the brain re-calibrates, but it takes awhile.”
I find it interesting that he references a Kalman filter, which is not part of the typical vestibular lexicon. For those interested, it is covered nicely in Susan Herdman and Richard Clendaniels’s new book Vestibular Rehabilitation, fourth edition.
What Dr. Reisman describes above would classify as a “visual preference” pattern, which often occurs after a vestibular injury. As vestibular specialists, we focus more on the functional impact of changes in vestibular function. It is interesting to see it explained from a human engineering perspective.
