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Brains that manufacture brightness and darkness

  1. Dec 12, 2003 #1
    It's amazing to realize that the world out there, beyond our retinas, is not at all bright even on a cloudless day in Arizona!
    And what's even more amazing is that even on a moonless night in a desert, the world "out there" isn't at all dark!
    It's our brains that manufacture brightness and darkness.
    Yes, I believe that our brains must specifically manufacture darkness rather than assume that darkness is automatically present in our brains when they aren't manufacturing brightness.
    For example, a person without a visual cortex (assuming that that's where "brightness" and "darkness" are created) would not even experience darkness. But a person without retinas may still experience darkness, it seems.
    So I wonder what makes a person squint when looking into the sun, is it the intensity of the light waves or photon streams that are hitting the retina, or is it the resulting brightness "manufactured" by the brain?

    Dan Jacob
  2. jcsd
  3. Dec 12, 2003 #2


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    Sounds like you're hung up on the very simple concept that sensation and perception are distinct processes.

    - Warren
  4. Dec 12, 2003 #3
    Yes, Warren, and it will take me a while to understand the distinction.
    Is there any way that you could guide me towards understanding where sensation occurs and where perception does (pertaining to vision)?
    Also, when I touch a hot object, what in this process is perception and what is sensation?
    Appreciate your responses,
  5. Dec 12, 2003 #4


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    Sensation happens at the receptor -- the retina in the eye, the tactile receptors in the skin, the taste buds in the tongue, the olfactory bulbs in the nose, the chocleal hairs in the inner ear.

    Perception happens in the brain.

    And you're correct -- a person with a functioning visual cortex, but without retinas, would still be capable of experiencing "dark," which is a perception. He would not be capable of sensing light, however, since he lacks the receptors.

    In the opposite case, a person with functioning retinas but without a visual cortex would not be able to perceive darkness, though he would be able to sense light. The sensation of light would be of no use to him, however, because he doesn't have the equipment to process those signals.

    Sensation is simply the act of gathering stimulus from the environment and transmitting it to the brain. Perception is a layer on top of that, in which those signals are analyzed and interpreted for meaning. Your eyes sense, your visual cortex percieves.

    In the case of person squinting at the sun: the incoming light creates a very strong sensation on the retina -- one that produces pain. The brain analyzes both the large visual stimulus and the pain stimulus, perceives that the eyes are being exposed to a bright light, and deals with the situation by closing the eyelids.

    - Warren
  6. Dec 12, 2003 #5
    Interesting post, djacob.

    First off, I'd like to mention something that is too often forgotten: darkness doesn't really exist (even as a perception) but is merely an absence of that which does exist (brightness).

    Now, because of that, a blind person doesn't perceive something in his visual cortex all of the time, but rather is unable to perceive with his visual cortex.

    Also, the distinction between sensation and perception does exist, but it may not be as clear-cut as you think. Sensation occurs immediately. Any external stimulus that stimulates a motor neuron is produces sensation. However, perception is usually (and I emphasize, usually) related to a conscious knowledge of the sensation that has just occured.

    For example, if I get pricked in the finger, I jerk back because there was a sensation (called "pain"). However, I have yet to percieve that I have been pricked.

    That's my two cents anyway.
  7. Dec 12, 2003 #6
    I agree with everything that you said in this post, except I need clarification on one thing: does sensation happen at the receptor, or when the motor neuron stimulates the spinal cord?
  8. Dec 12, 2003 #7
    If you look/understand at/it carefully enough you would realize that there is no darkness anywhere, the Universe ifs flooded with EMR (light) and even in the "Deepest of Caverns" that EMR is still there, radiating out, as heat......."There is no darkeness in Him"......

    ..as for the blind they do feel light, just usually as heat....ing.....
  9. Dec 12, 2003 #8


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    Sorry Mentat, I have to argue with you a little.
    That's not necessarily true. I can simultaneously perceive that half a room is bright, while the other half is dark (if I've blown up a light bulb). The perceptions are not mutually exclusive. If you don't like that idea, consider this one: I walk into a room that is dimly lit. Is it bright? Is it dark? It's neither. It's a mixture of both perceptions.
    If by "blind" you simply mean "without retinas," then this statement is false. A blind person can certainly perceive things. Close your eyes. In the absence of stimulus, your brain perceives all kinds of wacky things -- including weird shapes and colors and patterns. Whether or not those perceptions correspond to reality, or are based on real stimulus, is irrelevent -- blind people can still perceive.
    Motor neurons drive muscles. They aren't stimulated by sensation. You also don't need to invoke consciousness in this discussion.
    Absolutely false. Your brain interpreted the pain, and quickly determined what to do about it (jerk back). Some of these reactions are reflexes, though -- and the brain is not involved in a reflex reaction. Pricking your finger does not provoke a reflex. Observe that if you walk up to a comatose person laying in a hospital bed, you can prick their finger as much as you want, and nothing happens.

    - Warren
  10. Dec 12, 2003 #9
    What about "imaginary horizons"...like the event horizon of a black hole, or the "boundary" of the Universe? These should be completely "dark", in spite of having EMR within them. The reason is that "bright" as reference to our perception. Ergo, something is only "dark" if there is no percieved "brightness".
  11. Dec 12, 2003 #10
    Try "dark" because you cannot 'see' EMR, except when it is interacting with matter, scattering.....
  12. Dec 12, 2003 #11
    But that refers to the distinction in perception, not in objective reality. The room is "dim" because it is only partially "bright", not because there is the presence of some "dark particle".

    Actually, according to case studies (and some reading, on my part, of Helen Keller's biography and diary) blind people who have been blind from birth do not percieve those phenomenological "patterns" and "shapes" and "colors". They don't even know what a "color" is, except by definition.

    People who used to see, but don't anymore, OTOH, do indeed perceive as you say.

    So what neurons are stimulated by the sensation that send the signal to the CNS?

    I don't know that I can agree with this just yet. If you were to tap a comatose person on the knee, would their leg kick?

    BTW, I do think you are right about the brain being the one that interprets what to do when the finger is "pricked"...but then, isn't the difference between the "perception" and the "reaction" merely a conscious one?
  13. Dec 12, 2003 #12
    Thanks, Warren.
    Just clarifying the language makes for better communication.

    Would you think, as some do here, that darkness perceived by the brain is merely the absence of brightness?
    My feeling is that darkness must be manufactured by the brain just as much as brightness must.
    We are easily misled in assessing this question because we automatically equate darkness (internal phenomenon) with the total lack of EMR (external phenomenon).
    I believe that it takes the same amount of energy, effort, or whatever from the neurons involved to manufacture darkness as it does to manufacture brightness and as it does to manufacture grayness or color. So that darkness does not mean "neurons at rest."
  14. Dec 12, 2003 #13
    You know, I've got to agree with you here, even though I'm one of those that you mention. You see, if the neurons were "at rest" then there would be no conscious experience at all. However, if there was no EMR present, but still a perception (the perception of this lack of EMR) then this is what is called "darkness" and probably does require the same amount of "effort" for perception as the perception of "light".
  15. Dec 12, 2003 #14
    Just for clarity, there is always EMR present, everywhere you go, but, you cannot see it when it is traveling between source and reflector, (atomic mass) and we humans are not equiped to see EMR in all of its available ranges, hence the "idea(s)" of darkness.

    When you look at a Nightime Sky, realize it with your brain, cause it is the only manner to understand it, (It is not something anyone could literally 'see') what you 'see', and think is 'darkness', is actually flooded with perceptable 'white' (wavelength) light, but as it is in motion ( @C ) it remains invisible to the human eye.

    It is only when it interacts with atomic matter that it (What? slows?) 'scatters' enough that we percieve the "interactivity" as 'luminous' lighting. (...or when it is generated, we see that too, blindingly!)
  16. Dec 12, 2003 #15

    You're abs right, Robin.
    But what we're doing here with this thread, I think, are kind of "thought experiments." Like: "What if" experiments.
    We definitely cannot see photons in transit. Even the nerthern auroras are photons interacting with interstellar particles, and similarly are rainbows.
    Here's another "what if" question based on this thread:
    Suppose they put in front of you an infinitely large white screen and the sun is shining on it.
    In the middle of the screen, directly about ten feet from your eyes there is a one foot diameter red circle (filled in).
    Are some of the neurons in your brain specifically engaged in generating the red while others are generating the white (perception)?
    If so, then suppose we sent into your brain an army of nanobots to kill only those neurons that are associated with the red circle. Any neurons that were associated with vision within the circle are gone.
    What will you perceive now in front of you?
    Some will say: simple - you will have a one foot diameter blind spot.
    OK. Will the circle be black, white, transparent, or none of the above?

  17. Dec 12, 2003 #16
    Yes Perception and sensation, but after what Chroot wrote there wasn't much left to add......

    As for your "What if" from what I recall there is a "cluster"(?) in the brain where the neurons are doing a (very rapidly) comparision of the three primary colors as to establish an even/true color perception, destroy those and you would probably (Not certain) see in black and white only.

    As for the dot, good question, I would think that as the brain is very good at "filling in" (it is known to be doing this in everyones vision, right now..) so it might simply fill in the space as 'white' as included with/in the background.... Hard to test though.....any volonteers?

    P.S. Do you know the correct answer?
  18. Dec 12, 2003 #17


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    The eye is constantly making little scanning jumps, called "saccades" so it's scanning and sending signals to the visual cortex, and the signals are of various kinds. One contains information like (edge - sharp - continuous)) another says (white one side, red other), another says (no net motion) and so on. One of them also probably says (alert! alert! blood color detected in environment! alert! alert!) they don't make stop signs red for no reason at all.

    And the cortex puts these signals therough a multilevel net of interpretive nerves that interprets, gneralizes and integrates and passes on (big red dot on white background)(no danger inferred) to the rest of the brain.
  19. Dec 13, 2003 #18
    No, Robin, I don't.
    But I intend to ask the same question in another forum in which there are several neurologists and top philosophers like Hameroff, Chalmers, etc.
    If and when I get a reasonable answer, I will share it here.
  20. Dec 13, 2003 #19
    Cool thanks, but as a part of having "thought a little 'bout it", if your nano/bots go after "all red" will they then be taking out the cones in the retina(s)? after all they are just specialized neurons and the red (signal {or other quality?}) is produced there(?) and how would you keep them from going after the optic nerve? (as that would carry the red signal too, and would result in the loss of the black and white, from the rods)

  21. Dec 15, 2003 #20

    The scene I've described was very hypothetical and is close to being absurd. To make it even more absurd I'll say that each and every nanobot has a Ph.d. and is trained in distinguishing between neurons belonging to the optical nerves and those neurons that are involved with "creating" the red dot.
    Thanks for your thoughts,
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