Korte's law governs both your brain and flashing neon signsS

If you think that the psychology of flashing electric neon signs that say, "Live Nude Girls! ——->" is purely prurient, you are wrong. These signs are designed to take advantage of the way your brain perceives movement, and they do it using Korte's Law.

You've probably noticed, roaming at night through a city, that there are certain signs that light up in a particular way. A series of lights turn on one after the other, often forming into a circle, or an arrow directing people to an entrance. Anyone looking at it will get a perception of motion, a "light snake" moving around the sign. The perception is nearly impossible to shake, even though we know that there is no motion involved — it's just a series of lights being turned on.

We get the same idea when people at a stadium do "the wave," or flip over signs in sequence. Our brain interprets this series of events as a motion and calculates its direction and velocity. It's an illusion that does little harm, and probably some evolutionary good. Our ancestors need to know when an actual wave would hit them, or when the last of a flock of birds would take off. It is, however, still an illusion.

Psychologists started playing around with this illusion in the early 1900s. They quickly learned that timing was key — if people are shown lights flashing too quickly, they see nothing but a failed attempt at simultaneity. If the lights flash too slowly, they see two lights turn on, one after another. We have an intuitive sense of how fast things "should" travel to make them relevant to our sense of motion. It depends on a lot of factors but in 1915, Adolf Korte noted something interesting about it.

One might think that if the lights were very far apart, people might need to seem them flash nearly simultaneously in order to sustain the illusion of motion. The reverse is true. Seeing lights that are farther apart flash too quickly will destroy the perception of movement. Korte noticed, and memorialized in Korte's Law, that the farther apart two lights, dots, or events are, the more time needs to pass between the activation of the first and the activation of the second in order to preserve the illusion of motion. Apparently we have some sort of fixed idea of speed. If something violates that idea, we don't see it as motion anymore. We see this in everything from blown kisses to neon signs. The farther apart two independent events — one light and the next, the person who blows the kiss and the one who catches it — the more time we need to allow for the nonexistent motion between them. Our brains both set up the illusion and set the pace.

Via NCBI, Psychnet.