Why does travelling backwards make you feel ill?

We posed this question to Dan Parker from the University of Washington...

Dan - There are two basic reasons for motion sickness. One is, you have conflicting motion cues from the sense of balance in the inner ear, the vestibular system, and the eyes. The other problem is you get conflicting cues about your orientation. I've been studying which way is up most of my life and that's a problem. The effects of conflicting signals about how you're moving and how you're oriented are - you get dizzy. Why does riding backwards make you motion sick? The major reason is, if you're riding facing forward either in a bus, that you can see out of, in a car if you're a child, or you're on a train riding forward. If you are facing forward, you can predict, you can prepare for turns. You can see out the window and see the bank of the curve. If you're in a car, you can see where turns are coming up. You can predict what's going to happen and consequently, your ability to predict that you lean in to a turn. This reduces the disorientation that you feel. Why do people riding in backwards get motion sick? Because they can't make those predictions that you could make when you're riding forward. Diana - The same thing occurs when we get travel sick in the car. Your eyes, when looking at objects within the car tell your brain you're not moving whilst your vestibular system knows very well that you are. The two messages differ to the extent that you start to feel nauseous.