Normally, the vestibular system in your inner ear detects movement with fluid and sensitive hair cells, and sends that information through nerves to your brain.
On a rocking boat, my vestibular senses say I'm moving up and down, but if I'm looking at the deck, my eyes are telling my brain that I'm sitting still.
It combines things like vestibular sense, which is your sense of your head's orientation, and proprioception, your sense of where your body is and where it's moving, along with other touch-based sensations.
A chicken cannot move its eyes very much so their vestibular system keeps their entire head in balance so well that it can stay locked onto one position even as you move its body around.
" They tapped our bodies with hammers, twisted us about on special devices and checked the vestibular organs in our ears… They tested us from head to toe." By the time the tests were over, only 20 pilots remained.