Skip to: site navigation/presentation
Skip to: Thoughts From Eric

Illusory Spectrum

I know, I know, this is undoubtedly a widely known optical illusion, but I had to create and share my own version after stumbling across it in the wild.  Watch the animation cycle through all four frames, 2.5 seconds per frame.  Notice anything different about the spectrum when it flips from green as opposed to when it flips from gray?


The spectrum and greenish frames image are derived from Project Octant Part 13: Bug Hunt, which is where I saw this effect thanks to the Page Up key and the browser window being just the right height.  I hope Shamus won’t be too irked that I swiped copies to repurpose here.

Nine Responses»

    • #1
    • Comment
    • Tue 29 May 2012
    • 1548
    Robert Brewer wrote in to say...

    I don’t notice any difference. What effect do you experience?

    • #2
    • Comment
    • Tue 29 May 2012
    • 1700
    Alexander Graf wrote in to say...

    Same here, I’m not seeing any difference. I know I probably should, but I have been staring at this for 5 minutes and still nothing.

    Also, I have never heard of this optical illusion. Again, I probably should have…

    What should we see?

    • #3
    • Comment
    • Tue 29 May 2012
    • 1739
    Eric Meyer wrote in to say...

    For me, the post-green spectrum looks like it’s “zooming in” towards the green portion of the spectrum. Not the best way to put it, maybe, but I can’t think of another way to describe it. Post-gray, I don’t get that impression; it just pops into place.

    • #4
    • Comment
    • Tue 29 May 2012
    • 1808
    Ben R wrote in to say...

    Sometimes I think I see a slight effect where the block appears to lengthen slightly, which has a similar effect of the green “zooming”. But it is slight and doesn’t happen every time. Not sure if I’m just looking for something because I’m told to expect something.

    • #5
    • Comment
    • Tue 29 May 2012
    • 1833
    craig wrote in to say...

    I see the grey as ultra violet colours where the last green bit was which change out and then fade to grey. Must be the brain making assumptions on colour a bit like compression of images then re adjusting as it recognises the grey….

    • #6
    • Comment
    • Thu 31 May 2012
    • 0503
    Michael. wrote in to say...

    I didn’t notice anything. But now you mention the effect I’m ‘supposed’ to see I can’t not see it! Damn you sub-conscious! I covered all but the red end of the spectrum and it still did it. After I covered all but the blue end it didn’t do it.

    Now I’m going to go and do something else for a few hours, and then come back and see if I still see the illusion.

    • #7
    • Comment
    • Thu 31 May 2012
    • 0945
    Michael. wrote in to say...

    Great. Now I see it after both the green and the grey. I’m a strange individual I guess. ^_^

    • #8
    • Comment
    • Mon 4 Jun 2012
    • 1818
    Andrew wrote in to say...

    I actually thought the trick was that after viewing the green, the spectrum looked more desaturated. Did anyone notice that?

    • #9
    • Comment
    • Mon 18 Jun 2012
    • 1210
    Carissa wrote in to say...

    I thought the same as Andrew.

Leave a Comment

Line and paragraph breaks automatic, e-mail address required but never displayed, HTML allowed: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Remember to encode character entities if you're posting markup examples! Management reserves the right to edit or remove any comment—especially those that are abusive, irrelevant to the topic at hand, or made by anonymous posters—although honestly, most edits are a matter of fixing mangled markup. Thus the note about encoding your entities. If you're satisfied with what you've written, then go ahead...

May 2012
April June