0:00:06.891,0:00:08.119
Can you read in the car?

0:00:08.143,0:00:09.969
If so, consider yourself pretty lucky.

0:00:09.993,0:00:11.589
For one-third of the population,

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looking at a book[br]while moving along in a car

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or a boat or train or plane

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quickly makes them sick to their stomach.

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But why do we get motion sickness[br]in the first place?

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Well, believe it or not,[br]scientists aren't exactly sure.

0:00:22.296,0:00:23.842
The most common theory has to do

0:00:23.866,0:00:25.447
with mismatched sensory signals.

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When you travel in a car, your body[br]gets two different messages.

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Your eyes are seeing[br]the inside of a vehicle,

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which doesn't seem to be moving.

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Meanwhile, your ear is telling[br]your brain you're accelerating.

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Wait, your ear?

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Your ear has another[br]important function besides hearing.

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In its innermost part lies a group of[br]structures known as the vestibular system,

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which gives us our sense[br]of balance and movement.

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Inside there are[br]three semicircular tubules

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that can sense rotation,[br]one for each dimension of space.

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And there are also two hair-lined[br]sacks filled with fluid.

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When you move, the fluid[br]shifts and tickles the hairs,

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telling your brain if you're moving[br]horizontally or vertically.

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All this tells your body[br]which direction you're moving in,

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how much you've accelerated,[br]even at what angle.

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In a car,

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your vestibular system correctly[br]senses your movement,

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but your eyes don't see it,[br]especially when glued to a book.

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The opposite can happen.

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You're at the movies, and the camera[br]makes a sweeping move.

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This time, your eyes think you're moving

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while your ear knows you're sitting still.

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But why does this conflicting information[br]make us feel so terrible?

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Scientists aren't sure,

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but they think there's[br]an evolutionary explanation.

0:01:25.833,0:01:27.849
Fast moving vehicles and video recordings

0:01:27.873,0:01:30.264
have only existed[br]in the last couple of centuries,

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a blink in evolutionary time.

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For most of our history,[br]there wasn't that much

0:01:33.990,0:01:35.784
that could cause this sensory mix-up,

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except for poisons.

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And because poisons[br]are not the best thing for survival,

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our bodies evolved a direct[br]but unpleasant way

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to get rid of what we ate[br]that was causing the confusion.

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It's a pretty reasonable theory,[br]but it leaves things unexplained,

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like why women are more affected[br]by motion sickness than men,

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or why passengers[br]get more nauseous than drivers.

0:01:54.258,0:01:56.751
Another theory suggests[br]that the cause is more about

0:01:56.775,0:01:58.434
the way some unfamiliar situations

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make it harder to maintain[br]our natural body posture.

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Studies show that being immersed in water[br]or just changing your stance

0:02:04.306,0:02:06.677
can greatly reduce the effects[br]of motion sickness.

0:02:06.701,0:02:08.749
But we don't really know what's going on.

0:02:08.773,0:02:11.482
We know the more common remedies[br]for car queasiness --

0:02:11.506,0:02:14.341
looking at the horizon,[br]over-the-counter pills, chewing gum,

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but none are totally reliable

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nor can they handle[br]intense motion sickness

0:02:17.926,0:02:20.978
and sometimes the stakes[br]are far higher than just not being bored

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during a long car ride.

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At NASA, where astronauts are hurled[br]into space at 17,000 miles per hour,

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motion sickness is a serious problem.

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In addition to researching[br]the latest space-age technologies,

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NASA also spends a lot of time

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figuring out how to keep astronauts[br]from vomiting up their space rations.

0:02:36.377,0:02:39.582
Like understanding the mysteries of sleep[br]or curing the common cold,

0:02:39.606,0:02:42.634
motion sickness is one of those[br]seemingly simple problems that,

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despite amazing scientific progress,[br]we still know very little about.

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Perhaps one day the exact cause[br]of motion sickness will be found,

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and with it, a completely[br]effective way to prevent it,

0:02:51.915,0:02:54.017
but that day is still on the horizon.