Hack47.Keep Your Balance

Hack 47. Keep Your Balance

The ear isn't just for hearing; it helps you keep your balance.

Audition isn't the only function of the inner ear. We have semicircular channels of fluid, two in the horizontal plane, two in the vertical plane, that measure acceleration of the head. This, our vestibular system, is used to maintain our balance.

Note that this system can detect only acceleration and deceleration, not motion. This explains why we can be fooled into thinking we're moving if a large part of our visual field moves in the same directionfor example, when we're sitting on a train and the train next to ours moves off, we get the impression that we've started moving. For slow-starting movement, the acceleration information is too weak to convince us we've moved.

It's a good thing the system detects only acceleration, not absolute motion, otherwise we might be able to tell that we are moving at 70,000 mph through space round the sun. Or, worse, have direct experience of relativitythen things would get really confusing.

T.S.

4.5.1. In Action

You can try and use this blind spot for motion next time you're on a train. Close your eyes and focus on the rocking of the train side to side. Although you can feel the change in motion side to side, without visual informationand if your train isn't slowing down or speeding upyou don't have any information except memory to tell you in which direction you are traveling. Imagine the world outside moving in a different way. See if you can hallucinate for a second that you are traveling very rapidly in the opposite direction. Obviously this works best with a smooth train, so readers in Japan will have more luck.

4.5.2. How It Works

Any change in our velocity causes the fluid in the channels of the vestibular system to move, bending hair cells that line the surface of the channels (these hair cells work the same as the hair cells that detect sound waves in the cochlea, except they detect distortion in fluid, not air). Signals are then sent along the vestibular nerve into the brain where they are used to adjust our balance and warn of changes in motion.

Dizziness can result from dysfunction of the vestibular system or from a disparity between visual information and the information from the vestibular system. So in motion sickness, you feel motion but see a constant visual world (the inside of the car or of the ship). In vertigo, you don't feel motion but you see the visual world move a lot more than it shouldbecause of parallax, a small movement of your head creates a large shift in the difference between your feet and what you see next to them. (Vertigo is more complex than just a mismatch between vestibular and visual detection of motion, but this is part of the story.)

This is why, if you think you might get dizzy, it helps to fix on a moving point if you are moving but your visual world is not (such as the horizon if you are on a ship). But if you are staying still and your visual world is moving, the best thing to do is not to look (such as during vertigo or during a motion sickness-inducing film).

I guess this means I'd have felt less nauseated after seeing the Blair Witch Project if I'd watched it from a vibrating seat.

T.S.