Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about perception of color

  1. Apr 13, 2016 #1
    Hello friends, I'm discussing here with a guy about how we see color and stuff... he claimed two suspicious things and I want to ask you If it is true and If there is evidence of what he said... claim 1 and 2...
    I'm talking evidence, not hypothesis...can anyone help me here?
    just remembering that he is not a physicist

    1. objects emit or reflect a range of photon wave frequencies. The cones in our eyes receive three of these frequencies and create synapse electrochemical signals that assign colours in our heads.

    2. Through evolution an arbitrary combination has evolved to form a vision of "white" in our heads. There is no such thing as "white" in the real physical world. " <- is there any evidence of this assumption ? All I know from physics is that white is objectively real, we merely perceive it, he is saying something new for me, and using philosophy, not physics.
     
  2. jcsd
  3. Apr 13, 2016 #2

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    There's no "brown" either. It's all in our heads. At some level, everything is perception.
     
  4. Apr 13, 2016 #3
    I don't knw, How is brown outside of you then? White? What is the color of the object If there is no one perceiving?
    There must be a color outside of you but you can't know what is it.
    Perception is not reality, We perceive things, but things are not dependent on us to exist. And through our filters we see what is there.
    And from what I know, this is philosophy, not physics. we can't go beyond our eyes. And there aren't any 'images' in the brain.
     
  5. Apr 14, 2016 #4

    Fervent Freyja

    User Avatar
    Gold Member

  6. Apr 14, 2016 #5
    Look at a computer monitor with a powerful magnifier that has the image of the rainbow and a white screen. You will see the intensity of the colors of the pixels change as you look at the different colors of the rainbow. A white screen is produced when the three colors are at a certain intensity. Objects do absorb and reflect a range of frequencies in the visible spectrum according to their chemistry and molecular arrangement. The brain processes the impulses of the various visual receptors of the retina sorting them by intensity location and frequency and interprets them according to some genetic and learned program so we can tell the difference between a traffic signal and a rainbow.
     
  7. Apr 14, 2016 #6
    This statement is hard to justify. The light we perceive as "white" light is real, there's real EM radiation there, the object reflecting that light is real, so the conclusion, "no such thing as 'white'" doesn't make much sense.

    I think what the guy may be trying to explain is the concept of "qualia." But he's not doing a good job of it. The concept of qualia has to do with why we experience white (or any color, or any sensation) the particular way we do. Given that there's an objective external phenomena that cause some things to appear white (as opposed to brown or blue or whatever) why is it we have the exact experience of white we have? Why couldn't that same mix of light frequencies reflecting off that same object create the experience we think of as red, or some other experience completely unknown to us? Why does a certain frequency of light create the experience red, and not red? If you think about it, the only objective facts about the two colors is that there are two different frequency ranges and really, all you could expect is that the more energetic one should be a more intense experience of the other. The visual world really ought to be shades of grey only. In fact, though, we have this much more vivid and hard to explain experience of the differences. Red doesn't come from the chemicals in the eye receptors, but from how the brain processes the information from those receptors. It takes info from the red receptors, processes it, and feeds it back to us as red.

    Why couldn't the qualia, the subjective experience, of white and black be reversed, with surfaces receiving and reflecting more light appearing more dark and visa versa? There probably is no objective reason why not. We'd get used to it if that's the way it was from birth. The current subjective experience is simply the way it happened to play out, the way our brains evolved, and since it is useful, genes for that experience got passed on. The fact our brains make red look red, as opposed to red, is probably ultimately arbitrary, but it's quite wrong to conclude from that "there is no red." Red is real (light of a certain wavelength). There's just no single objective way it is constrained by physics to be subjectively experienced. The taste of salt might, in a different evolutionary train, have ended up being quite different than it is. In order for a sense to be of any use, it has to create some experience distinguishable from other sensory experiences. The actual subjective experience that gets created is most probably arbitrary, within limits, and many other subjective experiences might have served just as well. Of the choices mutations present, natural selection has left us with the ones that most contribute to survival (or are neutral).

    Qualia started out as a philosophical concept ("How do I know my red is the same as another person's red?"), but the subjective experience of color is known to be created in the brain, since certain kinds of brain damage will alter or even remove the ability to see in color even while the eyes remain unharmed. Check out Oliver Sacks case study of such a patient (scroll down past bibliography):
    https://people.rit.edu/wlrgsh/Sacks.pdf
    Indeed, all subjective sensory experiences are given their particular qualities by the brain. The brain takes objective stimuli and creates a subjective, but useful, experience.


     
  8. Apr 14, 2016 #7

    Jonathan Scott

    User Avatar
    Gold Member

    A couple of minor comments on the technical details:

    Each type of cone is sensitive to ranges of frequencies, not single frequencies, with a peak at different points in the spectrum.

    It's not really arbitrary; what we call "white" light (which can vary in different contexts) is when the balance of frequencies that we actually observe suggests that the light is spread fairly evenly across the visible spectrum, like sunlight, and a "white" object is one which appears to re-emit most of the incoming light without changing that balance significantly. (This assessment is of course subjective, and a "white" object in different lighting conditions may of course look very different in practice).
     
  9. Apr 14, 2016 #8
    There is a science to color. Even the way we perceive it, it is called the standard observer. Here is a introduction to tristimulus values and the standard observer. The standard observer is limited to a 2o field of view, as this is where the cones are most concentrated in the fovea.

    https://en.wikipedia.org/wiki/CIE_1931_color_space
     
  10. Apr 14, 2016 #9
    PS: All the colors we perceive can be represented by combinations of red, blue, green, and whiteness, darkness. Another point is that while pure light is additive, i.e. when you mix the three primaries at the right intensities, you get white light. However with pigments and dyes, it is subtractive, i.e. the more colors you mix, the darker (or dirtier) the resultant color is.
     
  11. Apr 14, 2016 #10
    Oh, yeah, I almost forgot about illuminants. Objects will appear differently depending on the illuminant. The standard observer includes D65 as the illuminant. It corresponds to white light produced at 6500K. There are also cool white fluorescent and incandescent illuminants. An object will appear to have a different color under the three different illuminants.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Question about perception of color
  1. Color and Perception (Replies: 45)

  2. Color Perception (Replies: 5)

  3. Perception of Color (Replies: 63)

Loading...