Persistence of vision allows you to see for nothing

  People always say that seeing is believing and that the eyes are the windows of the soul, but is this window really reliable?
  In 1825, a British physician named Paris invented something called a magic disk, which was to draw an empty birdcage and a bird on both sides of a disk through which a rope was passed, and then quickly twist the rope and turn it over. , There will be a very strange phenomenon-a bird in a cage.
  Do you think this is incredible?
  This is because vision is imaged by the lens of the eye, the cones are photosensitive, and then the light signal is converted into a nerve current, and then transmitted back to the brain to cause human vision. Since the formation of photosensitive pigments in the cone cells takes a certain amount of time, the image generated in the brain is slightly lagging. In fact, the brain’s response is half a beat slower than the eye’s response. This physiological “small defect” can give people an illusion. . After the effect of light ends, people’s vision will not disappear immediately. This kind of residual vision is called “persistence of vision” or “afterglow effect”.
  In 1912, German psychologist Max Wertheimer used a tachometer to project two bright lines on a black background in sequence, one vertical, and the other at 20 degrees or 30 degrees from the previous line. Degree angle. When the interval time is about 60 milliseconds, a peculiar phenomenon appears: sometimes you can see a straight line moving to another straight line; sometimes you can see the movement, but you can’t see the straight line. He called this phenomenon “like motion phenomenon.” According to historical records, the horse riding lantern in the Song Dynasty used the principles of persistence of vision and quasi-movement. It is a kind of lantern and is one of the toys of traditional festivals in China.
  In ancient times, horse riding lanterns were generally used on festive festivals such as the Spring Festival. Candles were lit in the lanterns, and the candlelight projected the paper-cuts on the wheels onto the surrounding paper. Gradually, the hot air generated by the burning of the candle will generate airflow, which makes the wheels rotate. In this way, the image will continue to move around, very lively and interesting.
  So seeing is not necessarily believing, and the brain may sometimes secretly deceive you.