Dear Dr. Universe: Why do you get dizzy when you read on the road? — Rebecca, 10

Dear Rebecca,

Without even thinking about it, humans can use their eyes, ears, sense of touch, and brain to keep their balance. But sometimes these senses get a little mixed up.

Imagine you are in the car reading your favorite book. All of a sudden the road starts winding. As you look down at your book, your eyes focus on the pages. The book doesn’t appear to be moving, so the eyes send a signal to your brain that you could be sitting still.

At the same time, something is stirring in your inner ears. Lots of tiny little hairs called cilia are inside your ears doing an important job: They help you sense how your head is moving in the world.

You also have some fluid that moves around these tiny hairs to help you with your sense of balance. The way this fluid passes over the hairs can send different messages to your brain.

It might let you know if you are upside down, right-side up, spinning, falling or perhaps, on a winding road. It’s part of a network you use to sense your movement in the world that scientists call the vestibular system.

That’s what I found out from my friend Robert Catena, a Washington State University researcher who studies all the ways the body maintains balance. When you are reading in the car, he told me, sometimes the vestibular system and the visual system are sending different messages.

“That’s what makes us dizzy,” Catena said when I visited him at the Gait and Posture Biomechanics Lab. “We have two bits of information that are in conflict with each other.”

He added that it’s easier to get dizzy if you aren’t the one driving. That’s because it’s harder for a passenger to predict the twists and turns of the road.

You may have noticed you can also get dizzy just from spinning yourself around. If you were on a merry-go-round at a playground, the fluid inside your ears would also be circulating around and around.

The fluid in your ears has inertia, so it keeps moving inside your ears for a short time after you get off the merry-go-round. The eyes say you are on the ground, but the fluid in your inner ear keeps moving and you feel dizzy.

I also found out that if you traveled to space, the vestibular system would work a bit differently. It is actually kind of hard to get dizzy in a place, where there is very little gravity.

After a couple days of floating around the International Space Station, that fluid would also start floating around inside your ears. The brain would adapt to this new environment, and you wouldn’t feel too dizzy or sick. I don’t know about you, but I think space sounds like a great place to read a book.

Sincerely,

Dr. Universe