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An Interesting Flying Illusion

If you are flying somewhere on a commercial airliner you can probably observe this neat illusion:

As your plane accelerates down the runway your inner ear will feel both the usual tug of gravity downward and the rearward pull of the "fictitious" inertial force due to your acceleration. The ear cannot tell the difference between these forces, it just reacts to their vector sum. The result is almost the same as if gravity had shifted direction slightly, or as if you had been tilted back.

How your brain interprets these signals depends upon what you look at. If you look down the aisle of the airplane it will seem to you as if the nose of the plane has lifted up in the air, even though the plane is still rolling down the runway with all wheels on the ground. You can verify this by looking out the window -- the horizon or the orientation of the buildings in the window frame will tell your brain that that the airplane is still perfectly horizontal. If you are quick enough, you can switch between the two views, and switch between feeling that you are being accelerated to feeling that you are going up a hill.

My interpretation of this illusion is that the brain uses cues from both the inner ear and the eyes to decide what is going on, but that the signals from the eyes are given more weight in the decision. To test this, try closing your eyes during takeoff, and try to decide whether you feel as if you are being accelerated or if you are going up a hill.


© Copyright 1997 by Eric Myers


Last modified: 10 December 2006 Copyright © 2006 by Spy Hill Research http://www.spy-hill.net /~myers/notes/Illusion.html