We had a fluorescent ‘magic lamp’ that flickered, but only when you weren’t looking straight at it.
Most of the precision viewing we do is in the degree or so around the optic axis of the eye. The eye’s optics are pretty poor off that line, and we have less cells in the retina off the axis because we don’t need them. This lack of focus also means we are better at noticing changes in average light levels in our peripheral vision. So, if we see a flicker in the corner of our eyes, that gives us a strong urge to look that way. That’s how the ‘magic lamp’ worked. If you fixate on an object, and don’t allow your eyes to move as they want, you will find the edge of your vision will fade as the information gets out of date. This is called the Fechner effect (he had several).
What’s an illusion? A lot of illusions are videos these days. You look at them once; you are told what to look for; you look again, and see something different. Many of them also demonstrate how our vision works.
