ELI5: How does this optical illusion work?

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It takes more time to see something dark. You move the picture. First the bright appears where you put it, then the dark gets visible. Also the Hard borders. Great contrast there. So easy and fast to process. The ol‘possum isn’t as rich in contrast. So more time to process.

Truft

The pixeled area messes with your peripheral vision and your eyes try to adjust. Make a binocular with your hand. look through it at the possum with the pixeled area blocked out. You will notice the possum stops moving funny.

sambmx17

You pick up your monitor and shake it. If you do that you lose, and the author get to take a victory lap.

Trax852

This is persistence of vision. If you’ve ever looked at a display with a high speed camera, you may notice that the screen isn’t always lit, it “flickers” This is especially true with modern displays where the pixels are self illuminating. The reason displays flicker is there’s no reason to keep a pixel lit up for longer that our eyes and brain need to see and process the image. As such, the possum which is already outputting very little light is firing very few photons at your eyes. If you shake it fast enough you’ll notice it disappears entirely. You can see this effect is stronger with lower refresh rate screens, and doesn’t occur on high refresh rate screens or printed paper. Edit: this answer is incomplete because it’s ELI5, the details get far more technical from here. I don’t see anyone downvoting giving a better explanation.

ThymeCypher

It’s not quite an optical illusion – it’s just as much a function of how the phone display works as how your eyes perceive movement. Darker, but not fully black pixels take longer to set – so when you shake your phone, the possum pixels move later than the surrounding ones. It’s related to “black smear”

yathern