Science Questions

Why does moving backwards make you feel ill?

Sun, 17th Oct 2010

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Kerrie asked:

I was on a train the other day in one of the backward-facing seats. I heard another traveler comment that when she rides for too long in these seats, she starts to feel a little ill. I've noticed that, too. And so I wondered why our brains don't seem to like moving backwards. Can you explain that to me?


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 FM-95A trainorientation.  I've been studying which way is up most of my life and thatís a problem.  The effects of conflicting signals about how you're moving and how you're oriented are Ė 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 whatís 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.


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Person's body sensors are synchronized to realate to and associate together.
Motion, moving forward associated the inner ear corresponding with the eye's view, the skin and muscle scening the direction of a normal everyday habit. Your body's sensors are naturally trained through habitual movement.

When any of these sensor deliver a different signal with respect to the other sensors your brain becomes comfused and you begin to get tired, dizzy, stomach gets queasy, may need to release some oral fluids that may project a few feet or meters.

I think you can train your brain to react differently, repetition and hard work. Or take anti vertigo medication prior to travel.  tommya300, Tue, 12th Oct 2010

I prefer to face backwards. That way, if the train crashes I'm thrown into the seat rather than out of it so it's safer. Bored chemist, Tue, 12th Oct 2010

Someone told me the better place to sit in a plane was in the tail section.
I asked why? I was asked, if I ever heard of a plane backing into a mountain. tommya300, Tue, 12th Oct 2010

Short answer:
The reason that sitting backwards on a train is more sickening than sitting forward is, perhaps, that you can see where you've been but cannot see where you are going. Hence, you remove some input data that could have helped your nervous system adjust itself more effectively.

Long answer:
My guess is simple, run of the mill motion sickness. Cars, trains, and boats are all relatively new phenomena evolutionarily speaking and, hence, can confuse our nervous system.

In particular, when it comes to motion, our brain takes balance and acceleration input from the inner ear, visual cues from our eyes, and movement/pressure input from proprioceptors in our body. Our neurological systems have evolved to coordinate all of these inputs (and perhaps others) to build a model of the world around us and how we are moving in it. This model is meant to be a predictive model. In other words, our brain takes in the aforementioned inputs and attempts to predict not only where we are now in space and how we are moving in it but also attempts to predict what future movement-related inputs should look like. Over time, it compares predicted input to actual input in an effort to improve/adjust its model.

Unfortunately, certain activities such as sitting backwards in a train, hanging out in a windowless cabin on a churning cruise ship (after eating a large, fatty pork sandwich slathered with BBQ sauce), or reading a book in a speeding car creates conflicting, incoherent, or wildly unexpected input. My guess is that the brain realizes that its predictive modeling efforts are not going well and, in response, passes along to us unmistakable error messages in the form of nausea, projectile vomiting, and other unpleasant feelings. The objective is to get us to stop doing the bad things that we are doing, those things that are confusing crap our of our brains.

The reason that sitting backwards on a train is more sickening than sitting forward is, perhaps, that you can see where you've been but cannot see where you are going. Hence, you remove some input data that could have helped our nervous system adjust itself more effectively. mlandri, Sat, 16th Oct 2010

The builders of the Glasgow Underground railway (a.k.a. "The Subway") solved this problem by making everbody sit sideways! Geezer, Sun, 17th Oct 2010

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