Of Two Minds

I’m teaching about opponent processes in color vision today and thought I’d share one of my favorite examples. This is how you use the human visual system to turn a black and white photo into color. Try it out:


  1. #1 MPhil
    July 1, 2009

    Very interesting.
    I learned about opponent color processing in a nice little paper by neurophilosopher Paul Churchland named “Chimerical Colors”, where he shows that the phenomenal color-space (the hue-circle with the added light-dark axis) is isomorphic to the output-space of the Hurvich-Jameson model for color-processing, thus allowing an ontological reduction of color-qualia to visual processing in an HJ-network. He even provided examples of “chimerical colors” where you look at a certain color, and then, instead of looking at a neutral background, look at a background of a certain (different) color, thus producing impressions of colors that we could not otherwise see. Very interesting – and impressive.

    One thing that has been bugging me, though – why do negatives of images always look like they have a far narrower color-range than the corresponding positive? Perhaps someone here can enlighten me.

  2. #2 Dan Clark
    July 2, 2009

    The apparent narrow color-range of a negative image is due to the dynamic range of the cone receptors in the retina. The three cone receptor types we have are differentially activated by a given color scene (the Wikipedia entry on color vision has a decent write-up of this). A negative of a given color scene has a very different set of wavelengths, many of which fall outside the dynamic range of human color vision of around 425nm-625nm.

    On another note, one thing that’s always impressed me is how each cone type has a nearly perfect tiling across the retina, irrespective of the other cone types.

  3. #3 The skepTick
    July 6, 2009

    Very cool! As the video is loading, I concentrate on the dot in the center of the image. When the image shifts to B&W, I can see the narrow color range, but I note that when I shift my focus off the center point, the colors go away, but return once I go back to the center. Is that an expected outcome?

  4. #4 Psikolog Uğur DALAN
    July 10, 2009

    ı concentrate on the center the image, ı see color range.

    it’s very interesting. Thank you

  5. #5 Marcia
    July 10, 2009

    This doesn’t work very well for me. When the image shifts, I think I may imagine a slight hint of colour, but when I acutally look at the image, it is black and white.

  6. #6 çocuk psikolojisi
    July 11, 2009

    Thank you. but ı actually look at the B&W image.

    Çocuk Psikolojisi

  7. #7 Marcia
    July 20, 2009

    I wonder why it works for some people but not others.

    To see an afterimage, I have to stare at an extremely bright light. A video on a computer screen in normal room lighting isn’t going to do it for me.

  8. #8 William Petersen
    July 21, 2009

    What happened to Shelley Batts? Is she married now? She never writes in this blog any more. How is she doing?

  9. #9 Llewellyn Kriel
    August 22, 2009

    I’m sorry, but I missed this entirely. All I saw was a black and white image – what else was I supposed to see?

  10. #10 Marc
    September 26, 2009

    Great blog! This video is now on my bookmark list and I’ve had a great time reading all your posts.

    Good luck with your PhD thesis.

  11. #11 JakeR
    September 29, 2009

    How does your research accommodate Edwin H. Land’s two-color representations (retinex theory), as opposed to standard three-color representations?

  12. #12 sikiş
    December 1, 2009

    I wonder why it works for some people but not others.

  13. #13 quang cao online
    December 28, 2009

    I wonder why it works for some people but not others.

  14. #14 Raleigh Chem Dry
    February 5, 2010

    I saw purples and blues and the blue did change some toward the end. But not sure if that was exactly what I was supposed to see.

  15. #15 bramki obrotowe
    February 9, 2010

    I can’t see nothing.

  16. #16 LivewithFlair
    June 28, 2010

    Greetings! I’m a Michigan alum who wrote a dissertation on the psychology of emotion and shame in particular. I’m fascinated by the brain and how emotions work. I blog at http://livewithflair.blogspot.com/ as a way to create happiness by finding the extraordinary meaning in the common thing. It turns out that you can change your mood much more easily than we think.

  17. #17 Haskel
    July 30, 2010


    Just like this clip is trying to make believers out of all of us via the “don’t believe what you see” theory, it is also manipulating viewers because seriously, you shouldn’t just believe what you see…

    Start video at 28 second mark which will reduce burn in time. Result is the same and theoretically it shouldn’t be because your eyes are “supposed” to stare at it for 20 seconds first to “burn in” the color from the negative.

    What do I see? It looks like creator has manipulated the still frames at 31 seconds, dropping in a couple 1/30 color slides. Some people perceive it while others don’t. It’s flash sublimination.

    To disprove this you should be given the option of watching the presentation backwards, but you can’t.

  18. #18 Brain
    January 17, 2011

    That’s awesome! There should be some instructions though to look at the dot… That might clear up some of the problems people are having.

  19. #19 Some one
    January 31, 2011


    Don’t be sceptic and the results will be amazing (look at the mirror)

  20. #20 Brain Supplements
    June 6, 2011

    Didn’t work for me either, but this opponent processing sounds very interesting, will be checking it out, cheers!

  21. #21 London Skeptic
    May 8, 2012


    I studied reverse-engineering MRI scans of the visual cortex, (V1-5) for my MSc project.

    That’s really interesting, and I’ll be following your posts with interests.


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