26 thoughts on “Three optical illusions

  1. I’m well within the boundaries of the “no tattoo for me, thanks” crowd. But that tattoo is just amazing.

  2. Interesting where the threshold for the number of dots is in the video – for me the illusion ‘worked’, instantaneously, when there were four dots. I went back and watched it with three, but it was much less clear to me. A) Any hypothesis for why this might be and b) how could you test it? – Matthew

    1. I get it with three as well, but as a triangle.

      Two doesn’t cut it. I guess the crossover of the two paths is too obvius at that point.

  3. I’ve become acclimated to tattoos, I guess, but have no desire to have one either. I am impressed with that tattoo, I wonder if the tatto illusion still “works” when the person is moving her arm.

  4. The circle illusion relies on timing of each dot. If the dots moved at different times, the illusion wouldn’t work.

    I know, I’m pointing out the obvious.

  5. That animated one is pretty straightforward; it’s just dots on the outline of a planetary gear. We mentally fill in the gear the same way we do the whole person from dots placed at the major joints.


  6. On the youtube website for the moving dots there is another short video-the ten best illusions(?)of 2014 and there is a perfect illustration of the moon illusion in the form of two pencils of equal length against a background of perspective lines.

      1. It always seems to me that a lot of people who get the more dramatic kinds of tattoo don’t think them through. How is that tattoo going to look in different contexts?
        – appearing first through a trapdoor?
        – on a bank teller, or any retail role?
        – masturbating, making out, making love?

  7. The circle illusion is al Tusi’s construction, which Jim al-Khalili claims influenced Copernicus. The smaller (in this case virtual) circle has just half the radius of the larger one.

  8. I’ve got two of my nieces staying (8 & 11). They loved these and wanted to understand all about how and why it works.

    A couple of years ago these same nieces were very worried for me. They go to a Christian school and told me I wasn’t going to live with the angels when I die because I don’t believe in God. Their parents convinced them I would still go to heaven because God would reunite them with the people they love, and Aunty Heather is a good person.

    They’re both intelligent and intellectually curious, so I think university will sort them out.

  9. That is some tattoo.
    We got past the “I’m 18 and I can have a tattoo if I want to and you can’t stop me!” stage by getting to know several of the local tattoo artists and their opinions of each other. That managed to tie her ladyship up in self-referential knots until she grew out of it.

  10. The third one isn’t what I’d call an illusion in the sense of a misperception by the visual system. It’s just math, and circles are exactly what you’d expect to see when plotting out-of-phase sinusoids against each other.

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