The Inner ear balance system in humans is so acute that it creates sea sickness when on a rolling ship or during similar un-natural movements. This is because the inner ear cavity contains a special fluid that remains always horizontal due to gravity. When we move our head one way or another this fluid touches or untouches the sides of the cavity which is covered with finely tuned nerve endings that send a signal to our brains telling us that our head is not upright. These natural modem signals are happening billions of times whilst you are reading this page. As a seaman I can confirm that one of the best remedies for seasickness is to concentrate on the horizon, because when the brain is able to see and concentrate on something naturally stable it is able to understand whats happening and why the incomming signals from the inner ear are so erratic.
Dolphins have an greatly enlarged inner ear cavity due to the diverse movements they are capable of.
The major difference in relation to humans is the up and down movement. Humans don't have this, we are always connected to the ground. Dolphins have a pretty hard time to see the horizon except when travelling and therefore jumping, both to breath and to fix the horizon. The Dolphin Sonar is used in conjunction with their ears to catch food. When this sonar hits the fish the fish tends to vibrate deep inside, these vibrations are slight but enough to confuse the fish and thats when the Dolpin gets his Brunch.