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What does a blind person see?

  1. May 12, 2007 #1
    a person born blind cannot tell you since he has never seen black.
    a person who becomes blind... what does he see?

    does he see black?... and if so.. why?

    if a person has absolutely no nerves going from the eye to the brain.
    does the brain register that as black? and why?

    black is supposed to be the sum of all colors. if you take all colors of the rainbow and mix them together. do you not get black?
    so black is not the lack of color but all colors seen at the same time.
     
  2. jcsd
  3. May 12, 2007 #2

    cristo

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    I have no idea about the actual question, but:

    No. Light coming to you from the sun is a mixture of "all the colors of the rainbow." Is this black?
     
  4. May 13, 2007 #3
    Objects are certain colors because they reflect those colors. For example, when viewed under normal unrefracted light, a rose will appear red, because it absorbs all the other wavelengths, but reflects red back to our eyes. A red rose viewed under a blue light will look black, because it absorbs the blue, but there is no red to bounce back. Therefore, black objects absorb all colors and reflect none. And white objects reflect all colors.
     
  5. May 13, 2007 #4
    completely blind people see nothing. they don't see black or gray or white... just nothing. i know it's hard to understand and I don't even pretend to understand it but that is what blind people respond with. I guess its like tetrachromic people... some things you have to experience yourself to understand.
     
  6. May 20, 2007 #5
    Depends on how he becomes blind. I think if your eyes get messed up the right way, you do indeed see black at first. Gradually I think your brain would adapt and you wouldn't see anything anymore. If the nerves or parts of the brain get damaged, weirder things happen.

    What do you see in your blind spot? There is a spot in your eye with no ability to detect light. It's toward the middle of your visual field so it should be obvious. But your brain fills in the spot as best it can. I know it sounds hard to believe that you would not be aware of a significant blind spot in the middle of your vision. Try this demo. The sudden realization of the blind spot is shocking!

    Some people who get damage to only some part of their vision actually get an effect like a blind spot, and things get "filled in" by their brains. Some people who are totally blind hallucinate. The brain is weird, wild stuff. Check out some books by V. S. Ramachandran. I promise you won't be disappointed.
     
  7. May 21, 2007 #6
    Tell me if this isn't close.

    By closing one eye for a bit, your vision seems to be entirely diverted to the other eye. I'm thinking what you see with the closed eye (nothing, not even blackness) is approximately what it's like.
     
  8. May 22, 2007 #7
    A congenitally blind person sees the same thing with their eyes that you see with your elbow.
     
  9. May 22, 2007 #8
    I don't know... the seems brain to still fill the gap with whatever the surroundings are (invert the colors of your screen, and the blind spot is no longer grey).

    :rofl:

    another great thing to try with that demonstration is slide your finger on the screen up through that O. suddenly the tip of your finger disappears! then as you keep sliding it out of the blind spot, there is a grey are cutting your finger into 2 pieces! ... using a ruler you can measure exactly how big the blind spot is (it increases with distance)... all this is not reassuring at all: were a truck approaching you through that path, you would certainly not see it until it's too late (assuming your eye is fixed on something for some reason... and it was a really silent truck... and you were covering your other eye— still better chances than winning the lottery).

    Does anyone know a blind person who was born blind? asking is the really only way to settle this. The closest I know is a friend of mine who's legally blind... but he can still see (poorly) out of one eye and he wasn't born that way either so it's no use asking him.— come to think about it I know two people who are blind out of one eye... three actually!: I remember my middle-school french teacher would go blind on one eye sometimes (I don't remember why; it was some sort of medical condition)... I guess I attract half-blind people?
     
  10. May 22, 2007 #9
    Wouldn't someone who was blind simply ignore the sense that they do not have?

    I was under the immpresion the you were actually seeing the under side of your eyelid without light, so it appears black.
     
  11. May 22, 2007 #10
    I know what black "looks" like, so I don't think I a person born with vision can really experience it to understand.
     
  12. Jan 14, 2010 #11
    One see with one's brain, not the eyes. Eyes only provide input.
     
  13. Jan 25, 2010 #12
    A blind person sees absolutely NOTHING! It's another matter that nothingness gives the impression of being black but it's just no colour and it's nothing.

    To answer your question from a different perspective, it depends where has the person gone blind actually. If the person has gone blind by suffering a lesion of posterior cerebral cortex, he's not completely "blind". Light perception exists as well as SOME patterns of movements that are associated with light. That's because visual information is also processed in midbrain, not just the brain.

    Try closing your eyes and you have come slightly close to being blind. But not close enough because by closing eyes, you are irritating the peripheral rods and providing some stimulatory input. When you close your eyes forcefully and roll them, you can even perceive the retinal arterial bifurcation patterns. You also retain the residual stimulation from the visual input you were receiving when eyes were open.

    Just minus all of these, and the person is blind.
     
  14. Jan 25, 2010 #13
    True, but your eyelids cut off the light. To see anything (or in other words, to NOT be blind), you have to view the light. The other way around is IRRITATING the rods and cones. Imagine a situation in which 100% light is cut off (I know this is not possible in real life but just assume). In that case, you are as good as blind other than the residual photoreceptor irritation that might be present.
     
  15. Jan 28, 2010 #14
    If you asked a person who lost their sight what do they "see" isn't that the best chance at understanding what a blind person "sees".

    I don't think the fact that they had sight previously disqualifies them from the chance to answer the question.

    I bet it's the same as we experience. I read somewhere that when you close your eyelids to blink a message is relayed to the brain to shut off that particular sense for the millisecond you are blinking, everytime! It does this because it would get crazily annoying & distracting to have to deal with interruptions every few seconds.

    A person who never seen in his/her life would have no appreciation of what light is (in terms of vision) - I assume - and would not have developed that part of their senses - I assume, but to assume that they experience something alien to what we understand is a bit....

    Visionopocentric, or maybe oculopocentric lol

    My intuition tells me that these people are just more mentally & unconsciously involved with their other senses, as it's a question of life & death in a sense & humans are known for adapting to particular situations when it's that important. Maybe blind people do feel an emptiness in that regard, I could be wrong, but I think that the nothingness we imagine them to experience is just us extrapolating from our heavy reliance on sight.
     
  16. Jan 28, 2010 #15
    I can't answer for a blind person because I see perfectly fine. However, I do a weird thing that can give some insight here. When I read or use a computer, I shut my left eye completely. I do this unconsciously because of a slight nerve damage in the left eye that makes it hard to turn that eye inward. This, combined with poorer vision in the left eye, has triggered my brain to shut the left eye without even thinking about it. I don't even notice it, even after working all day on a computer.

    The critical information here is that I don't see black in my left eye. I have no sensation of anything from the left eye when it's closed. When I lift my head from a book, or computer, my left eye opens and i see fine with both eyes. If I shut both eyes, I see blackness.
     
  17. Jan 30, 2010 #16
    Imagine a sixth-sense that you don't have, you know nothing about it, you receive nothing from it, when some body misses his vision sense, he no longer receives or feels it, so I think he doesn't see blackness or any thing else.
     
  18. Nov 1, 2010 #17
    Yeah another sense organ does seem possible...

    But... I thought that maybe there was something peculiar about touch and sight. We feel [I take this to mean we are embodied in] and see empty space and IMVHO the space that these senses engage with cannot be done away with...

    What would it mean to be walking along from A to C and when we get to B we are not in space? Errr, don't answer that...

    And what would it mean to see absolutely nothing in an area in our visual field: I can imagine not being conscious of it but it's still there; even if whatever integrates the information from two eyes does not know that it has a blind spot it is still effected by it... and it seems to me that that would be visual. See, you can't stop someone seeing something or other [even darkness that we don't pay attention to] where some space is, whereas sound can be blocked without using sound.




    I actually think this is a metaphysical [I think that's the right word] fact, that there is something about visual space that means it can't be destroyed. Kant might mean something like this
    but it seems unlikely as he does not give the consequence that we can't really die. But that's the sort of thing I mean, something that would make it so that we don't stop seeing something even when dead.
     
  19. Nov 2, 2010 #18
    A totally blind person sees the same thing that we see out of the back of our heads, nothing. Not blackness, but nothing.
     
  20. Nov 3, 2010 #19
    i congenitally blind person maybe but i think that yeah i don't normally "see" out of the back of my head but i'm still aware of if visuospatially.
     
  21. Nov 9, 2010 #20
    I wonder if blind people during REM sleep experience something other than nothing if nerves in the optic nerve fire?( thats if they do fire however) :-)
     
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