Question

How does the human body maintain a sense of body position and balance on Earth, while flying in an airplane, or traveling through space?

We use a variety of clues to maintain balance and orientation. The main ways to sense our position are from visual information and from the output of the part of our inner ear that senses that direction of gravity. When these two sources of information conflict, we can become disoriented or even nauseated. This can happen when our visual references change, as exploited in some carnival "fun houses", or when we lose the gravity sense in free-fall in space. When our gravity sensor tells the brain that we are falling while visual references remain normal, space sickness can result. Fortunately, this condition usually passes quickly, and there are now also drugs to alleviate the symptoms. In airplanes, it is also possible for the whole body to sense acceleration (as in turns) from the force we exert on our seat -- the origin of the term "flying by the seat of your pants".

David Morrison
NAI Senior Scientist
August 24, 2005