This is amazing.  The blue and the yellow bars are ALWAYS going around at the same pace.  However, when the disk is placed behind them, they appear out of step.

The explanation is far from simple and can be found here.

Do you like it?



    1. Nice once! Interesting that the “trivial” explanation (luminosity contrast) doesn’t seem to be entirely valid, as the PDF on the explanation page says.

      The site Richard linked to has a great many more illusions –

      Check out the spiral (number 8) for the hangover 🙂

  1. Brilliant. Nothing like frying my brain first thing in the morning. I always try & fight the efffects of illusion…….. & fail. 🙂

  2. That’s fun. As an artist, my first impulse is to say, ‘Yes, I do similar things with contrast and/or complementary colours’ but that only shows that instinctively one sort of knows it works but doesn’t explain the why or how. My assumption is that it’s to do with the rate of change that the cones in the eye can process, but I don’t really know what I’m talking about.

  3. While I see the illusion, it looks like it has to do with the very poor contrast of the yellow block on the white vs excellent contrast against the black. The yellow blocks gets washed out and partially blends in with the white – this gives the appearance of the block disappearing and then jumping to the black. If I focus on just the blue, its speed looks constant. But when looking at both, the apparent jumpy motion of the yellow makes the blue also look jumpy in the opposite direction due to the relative motion.
    Nice effect.

  4. Dear Sir or Madam,

    I cannot open the links attached in Richard’s e-mails. Normally I highlight the link in the e-mail and I am offered to “search “for it in google which can do the trick.
    Today it cannot be done…..
    Advanced searchYour search – watch?v=1coheuM0IqE – did not match any documents.


    •Make sure all words are spelled correctly.
    •Try different keywords.
    •Try more general keywords.

    Is there a problem with my system or with the links.
    I really enjoy Richards blog and would love to be able to read it.

    Thank you

  5. When I looked at the version on the Michael Bach site I found the illusion seemed far more pronounced when the feet were travelling from left to right than when they went from right to left! (in fact the illusion hardly seemed there at all). Anyone else experience this? And anyone got any explanations?

  6. I got them to go around in sync but it was quite difficult. After a few tries I learned to try to focus intently on both blocks at once by staring at the spot in-between the blocks. Then, try to get your mind to watch the blocks and somehow not to see the disc.

    It’s tricky at first but once you get it you will be surprised to see the blocks moving smoothly instead of in step.

    Great illusion.

  7. Meh. Pretend for a moment that the blue and yellow are black and white, and the reason for the illusion is obvious. I could make them go in sync, but only by concentrating on the position of the yellow one and noticing that it was moving even against the white background.

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