Flash fusion means that we see a series of flashes. When the number of flashes per minute increases to a certain extent, what human eyes feel is no longer flash, but a fixed or continuous light. Visually, this phenomenon is called flash fusion. More generally, when the stimulus is not continuous but intermittent, with the increase of intermittent frequency, it is no longer intermittent stimulus, but continuous stimulus. The minimum discontinuous frequency that can cause a sense of continuity is called the critical frequency.

Its physiological mechanism is the persistence of human vision, and pretending to be B is the afterglow effect. When the human eye observes the scene, it takes a short time for the light signal to enter the brain nerve. After the light effect, the visual image did not disappear immediately. This residual vision is called "afterimage". For example, drawing a lit incense in the air at night will leave traces (positive and negative images), or you will stare at the picture below. After a while, you will find a white wall blinking, you will soon see God (negative afterimage) ... and you can also see Zhenzi (Baidu picture: visual afterimage). ...

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