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Neurophysiology of color

  1. Jan 13, 2004 #1

    selfAdjoint

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    In the theory of everything section of the MKaku forum, I asked Nereid about the physiology of color, especially the bands detected by the cones, and she responded as follows:

    Some sources for colours and bands, in general (probably gives you more than what you asked for) :
    http://www.photo.net/photo/edscott/vis00010.htm
    http://ergo.human.cornell.edu/stude...pdfs/vision.pdf
    http://www.yorku.ca/eye/specsens.htm

    Here's one article on the sex differences (looks like some women may have 5 different types of cones - blue, two green, and two red):
    http://teachpsych.lemoyne.edu/teach...olor_vision.htm

    How does this happen? The genes for cones are on the X chromosome, and women have two. What if the expression of a red cone in one cone is different from the expression of that in a neighbouring red cone?


    Since theory of everything is inappropriate for a discussion on this topic, I am starting this thread here.

    I think we can take it as given that Nereid's links pretty well cover the subject of the cones, their spectral range, and the connection to genetics. What I would hope to see here is discussion of the neurophysiolgy of color processing in the brain, particularly how the color sense is created - how does the merged info from the cones get built into a unitary sensation?
     
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  3. Jan 14, 2004 #2

    Another God

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    I have a pet theory that our sensation of colour is actually a function of the brain based on internal comparison of experiences. I think that the brain records all visual inputs of wavelengths, storing them all and over time building a database. As this database builds up the brain compares all of the different wavelengths, categorizing them as similar or different. And from this classification it learns to differentiate them. The final step is arbitrarily assigning an experience for each wavelength input. So the expereince of colour is not necessarily the same for any two individuals, although the effect of that experience will always be identical.

    Thats just a pet theory with no evidence though.
     
  4. Jan 14, 2004 #3

    selfAdjoint

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    some google results

    One key researcher in the field seems to be John Krauskopf.. Back in 1984 he coauthored a seminal paper that set up the protocols and color coodinate system in which later papers have discussed their results. This paper is not online, but a description, including the coordinate system, is here. A more recent paper by other authors is here.

    The basic facts seem to be that the lateral geniculate nucleus has cells that decode the cones' input by differencing them, and the striate cortex has cells that respond to physiological hues. The last paper seems to infer that the LGN feeds the striate cortex.
     
    Last edited: Jan 14, 2004
  5. Jan 14, 2004 #4

    Njorl

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    It may not belong on this thread, but I have laways wondered why we can only see one octave of color, but hear many octaves of sound.

    Njorl
     
  6. Jan 14, 2004 #5
    But we are limited by the pitch of sound we hear.

    nautica
     
  7. Jan 14, 2004 #6

    Njorl

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    Yes,I know, but I think we can hear about 6 octaves of sound, but we see only one octave of light.

    Njorl
     
  8. Jan 14, 2004 #7

    selfAdjoint

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    Years ago, in the Scientific American I saw an answer for that.

    The minimum energy photon we can see is one with just enough energy to raise one electron in the outer band of a rhodopsin molecule to the next higher energy level. That's deep red.

    The maximum energy photon we can see is just lower than the energy that would raise an inner electron of rhodopsin to a higher energy level, and thus disrupt the molecule. This energy is in the deep violet.
     
  9. Jan 14, 2004 #8
    How can one ascertain a claim by the blind that they imagine color?
     
  10. Jan 14, 2004 #9

    selfAdjoint

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    Possibly use fMRI to examine their brain states while they are imagining different colors? Compare with similar examinations of sighted persons visualizing colors?
     
  11. Jan 17, 2004 #10
    neurophysiology of vibration

    Njorl - we hear 10 octaves of sound, for 10/1 ratio with light; while light counters with a speed ratio of 909,090 to 1.

    selfAdjoint - "The maximum energy photon we can see is just lower than the energy that would raise an inner electron of rhodopsin to a higher energy level, and thus disrupt the molecule. This energy is in the deep violet."

    Here is another "theory" that excludes the existence of magenta. Unlike red, violet does not trail into darkness, it fades into white.
    The interval of the fade is typically called lavender, and has the highest energy currently allowed "in the box" model of visible light. (excluding white and magenta -- still theoretical )

    last but not least:
    Loren Booda - with a last name of "Booda", you should know that there is a place between "open eyed" seeing and "closed eyes imagination" that sees pure color. It is some times called the "third eye", and is accessed and controlled through meditation. (meditation = brain waves @ less than 7hz ... 1/3 of "normal consciousness" This suggests to me that the same pattern recognition that allows enjoyment in listening to music, and discernment of color, is "hard wired" into us as human beings since we too are "characters of vibration." So, even people blind from birth, should be able to visualize color. Whether your orange is their blue, or something, is another story.

    LPF
     
  12. Jan 17, 2004 #11
    The Case Of The Colorblind Artist

    Anyone interested is how the brain creates color from frequency differences will be interested to read The Case Of The Colorblind Artist, the first chapter of Oliver Sack's book An Anthropologist On Mars.

    The artist suffers a head injury in a car accident. Soon afterward he loses his ability to percieve colors:

    "It was not just that the colors were missing, but that what he did see had a distasteful, `dirty' look, cavernous-everything wrong, unnatural, stained , and impure.

    Mr. I. could hardly bear the changed appearances of people (`like animated grey statues') any more than he could bear his own appearance in the mirror: he shunned social intercourse and found sexual intercourse impossible. He saw people's flesh, his wife's flesh, his own flesh, as an abhorrent grey; `flesh colored' now appeared `rat colored' to him. This was so even when he closed his eyes, for his visual imagery was preserved but was now without color as well."

    Sack's short history of the neurological perception of color worked into this chapter is fascinating. I was surprised to find how much Heimholz and Maxwell had contributed, since they're better known for electromagnetic persuits.
     
  13. Jan 17, 2004 #12

    selfAdjoint

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    Thanks Zooby, that gives me just the hook I need to link to Sack's fine essay on consciousness in the New York review of Books. Is consciousness continuous or discrete? what did James think, what about Bergson? Sacks has some of his wonderful patient stories to tell, and a review of some current consciousness research.
     
  14. Feb 5, 2004 #13
    Selfadjoint,


    When you asked "Is consciousness continuous or discrete?", what type of consciousness do you mean? It is hard to define. For instance, right now your attention is focused on reading this line, but you may be aware of a radio, or TV in the background. In this example, "aware", and "attention" are both part of consciousness. From this example, aware consciousness is continuous, but the focusing of attention is discreet.

    Making it even harder to quantify: focusing on your awareness (meditation). When this is learned, practiced, and mastered, a new form of "continuously discreet" consciousness pops up. I call it this because you can really never stop the mind from having thoughts, however, you can over-ride your normal response of following the thought through its' logical conclusion, and "let it pass by your attention" without response.


    LPF
     
  15. Feb 6, 2004 #14

    selfAdjoint

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    In my post, I wasn't asking the question but indicating it was one of the topics in Sack's essay. I personally think that consciousness is the product of many overlapping, interacting, distinct processes - more or less along the lines of Dennet's "Consciousness Observed".
     
  16. Feb 9, 2004 #15
    more on thread title...


    When I was a kid, I had a friend who had "shaky eyes". I don't remember what this is called, but it looks like a fast left to right vibration. I have seen other people with this since then. I asked him if he "saw" things in a shaky way, he said no. His doctor had told him that his brain automatically adjusted for this, and produced a still scene (like auto stabilize on video cameras).

    Related example: You can disrupt this "auto stabilize" feature by bringing resonant waves into proximity of vision. While looking at your computer screen, and humming a deep, low E note?, it slows down your perception of the screens' refresh rate, causing it to appear blurry and shaky. I have done this with a dremmel tool touching where the neck and head meet, directly behind the eyes. It is like an old TV that someone tweaked the verticle hold on. This seems like the opposite of the former, so that your ability to perceive each individual screen "rolling" by increases. Does this sound right?

    This, combined with the knowledge that our eyes can not perceive the difference between a pure color, and the same "color" that is a combination of other colors, suggests that we live in a place balanced between abilities that are as varied as our environment. There are elements of "enjoying" what we see, and warnings of potentially harmful things, all left to our perception. This can be thought about questioned, but initially at least, the autonomous mind is running the show. So our conscious, thinking mind is actually interpreting perceptions that are automatic. Our variety then comes from the different ways a perception can be interpreted, AND from our physical limitations/abilities in receiving the signal.

    LPF
     
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