One important function of your inner ear is stabilizing your vision when your head is turning. When your head turns one way, your vestibular system moves your eyes in the opposite direction so that what you are looking at remains stable.

To see for yourself how your inner ears make this adjustment, called the vestibulo-ocular reflex, hold your thumb upright at arm’s length. Shake your head back and forth about twice per second while looking at your thumb. See that your thumb remains in focus.

Now create the same relative motion by swinging your arm back and forth about five inches at the same speed. Notice that your thumb is blurry. To see an object clearly, the image must remain stationary on your retina.

When your head turns, your vestibular system very rapidly moves your eyes in the opposite direction to create this stability. When the thumb moves, your visual system similarly directs the eyes to follow, but the movement is too slow to track a fast-moving object, causing blur.