Photo: Bob Cotter (Flickr)
It can happen at a carnival or on the dance floor–that moment when you stop spinning and the world starts spinning around you.
Spin Spin Spin
We don’t often think about keeping our balance but doing it involves the coordination of several different senses. Our muscles alert the brain if weight is suddenly thrown one way or another. Our eyes tell us if the horizon seems to be tilting. And inside our ears, tiny fluid-filled organs called the “semi- circular canals” detect sudden movements of the head as the fluid sloshes one way or another.
One way these organs work together is that when the semi- circular canal senses that the head is turning rapidly to the left or right, it automatically signals the eyes to move very quickly back and forth. That makes it easier to keep focused on objects that would otherwise be blurred as they went past.
To prove this to yourself, sit in a swivel chair or a merry- go-round and close your eyes. Press a finger against one eyelid so you can feel the eyeball moving underneath. Then have someone give you a spin and you’ll feel your eye moving rapidly back and forth.
When you stop spinning, the fluid in the semi-circular canal is still sloshing around. So it continues sending the message to the eyes, which keep on moving. But now, instead of making a rotating world seem like it’s standing still, the eye movements make a stationary world seem like it’s spinning.
Incidentally, people whose semi-circular canals don’t work properly sometimes have more trouble balancing, but they also don’t experience the automatic eye movements when they’re spinning. So when they stop, for them, the world stands still.