Three sources of balancing information

Three sources of balancing information.
The first source is proprioceptive sensors in our muscles that tell our brains where the parts of our bodies are in relationship to each other. The second source is the tiny hairs in our inner ears called cilia, the vestibular system, that tells us how our heads are positioned. The third source, and probably the most important, is our eyes. Eyes tell us which way is up and which way is down.

Spinning chair and balancing platform.
The spinning chair is called a centrifuge. The balancing platform is known as the "balance booth" but is actually a "posturography system."

http://liftoff.msfc.nasa.gov/news/2003/news-balance.asp