Ever had that strange feeling, sitting on a train, where you see another train moving and you think that you are in motion instead? There's an actual term for that feeling. And you need just the slightest stimulation to feel it.

Illusory motion comes from all kinds of different sources. Sometimes it's internal - we feel the room swaying when we stand up suddenly (or when we fall in love, if we're cartoon characters). Sometimes, when we get off of boat trips or long flights, we take a while to get "land legs," as our body compensates for a ground that isn't moving anymore.


And then there's a kind of motion we can easily induce. Anyone who has sat in a train or a plane and seen another train or plane move along outside the window has felt it. It's called "vection," and it shows how completely our brain will induce a physical feeling, if that's the feeling it believes we should be experiencing. It turns out that vection can be induced with any sufficiently decent screen and some scenery. Experimenters can put make people believe they're spinning in a circle, zipping back and forth, and even turning nearly upside down. And they don't have to try that hard. They don't need to simulate the edges of a window, or a cockpit. All they have to do is make slight marks, right on the screen, that the person will adopt as their "point of view," and then move the scenery around behind it. The brain does the rest.

Vection is interesting in terms of perception, but it's mostly used for motion sickness trials. Making people sick in a room with a screen is much easier, cheaper, and safer, than actually putting them in situations where they feel motion sickness. Most of the sea-sickness or air-sickness medication you take is tested in a stationary room on people sitting in a chair watching movies of motion.

[Via Vection and Simulator Sickness, Enhancing Visually Inducted Self-Motion, Effects of Ginger on Motion-Sickness.]

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