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Medical Blind people see blackness?

  1. May 29, 2006 #1
    Do blind people see blackness?

    (and before u say, "no theyre blind", please think about it!)
  2. jcsd
  3. May 29, 2006 #2
    If we define "see darkness" to be "not seeing anything", then they do see darkness, and hence under normal circumstances we never see darkness but, say, [tex]\epsilon[/tex] unit of light for some [tex]\epsilon >0[/tex].

    In addition, we can say that blind people see darkness continuously, and we only see darkness periodically, assuming that light is made up of dimensionless particles and time is continuous.
    Last edited: May 30, 2006
  4. May 30, 2006 #3
    And what about animals without any eyes, do they see blackness aswell?
    Do plants?

    Just wondering...
  5. May 30, 2006 #4


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    My guess would be that blind people don't experience visual blackness, or anything in the visual modality for that matter. For instance, a better analogue for the visual experience of a blind person (at least one blind from birth, I'd imagine) might be not blackness, but rather, the same visual experience you have of the area in the back of your head. Blackness is a visual experience, even though it usually connotes absence of light. What you see at the back of your head is more like complete absence of any visual experience at all.

    Of course, that's just conjecture. The best way to answer the question would be to ask someone who was born blind but later had vision restored.
  6. May 30, 2006 #5
    With 'the blind from birth' part, u mean that when one hasnt ever experienced light, then one still sees blackness but doesnt realise it because one cant compare it with light (since one cant imagine what light looks like).

    And for people who have not been blind from birth, they can compare their no-light-blackness to their memories of once experienced light.

    So in short: what turns nothingness (no light) into somethingness(blackness), is the experience of light.

    Though people who havent been blind from birth may also experience this as nothingness, they are atleast capable of turning it into blackness if they tried hard enough. Perhaps with some trying, we non-blind people could also turn the back of our head into blackness.
    Last edited: May 30, 2006
  7. May 31, 2006 #6


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    Yeah, same here. Its like asking "what do deaf people hear?" Completely blind people, can't see anything. Not even black.
  8. May 31, 2006 #7


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    I imagine it would depend why they are blind. I don't know much about the reasons for blindness but I imagine it can either be caused by the eyes or by the brain.

    If the eyes themselves are damaged then it would be the same as you being in a very dark room, that is no photons are hitting your eyes so the eyes don't send any signals to the brain and you "see" darkness.

    If it's part of the brain that's damaged then I guess they wouldn't see anything. It would be as if they don't have the sense of sight at all.
  9. Jun 1, 2006 #8


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    It's not necessarily that simple. The visual cortex requires proper visual inputs and motoric interactions in the world on the basis of that visual input in order to develop properly. In the absence of such input from birth, visual cortex proper would likely be subsumed for other perceptual/cognitive processes. I find it unlikely that such a radically different "visual" cortex would support anything like the subjective experience of vision (of which blackness is a type).

    For people who developed blindness well into life, it's likely that they at least have the capacity for visual experience. Whether or not they actually experience visual blackness or no visual phenomena at all, and how this unfolds as a function of time spent in blindness, is really an empirical question that would be best answered by asking for the introspective report of a suitable person. Whatever the answer turns out to be, though, a significant part of the story should be the physiological state of the brain regions that normally support visual experience. It's not just a matter of simple cognitive comparisons.
  10. Jun 1, 2006 #9
    It would depend on why they are blind.

    I would think that blind people are unable to see blackness. My reasoning for this is that sighted people are not able to see blackness. They can only see light. If there is no light hitting your photo-receptors (retina?) then the eye will not send nerve impulses to the brain, so blackness is not something that can be seen.

    Maybe this view is applicable to clams, jelly fish, plants, and rocks. I'm not really sure.
  11. Jun 1, 2006 #10


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    There are varying degrees of photosensitivity among animals. On different levels, you can actually trace the evolution of the mammalian eye. Some merely have mildly photosensitive patches of skin cells, more advanced types have crude retinae, others add a lens to the system, etc.. Insect compound eyes seem to be in a class by themselves, but I'm not sure.
    Since plants aren't conscious, I doubt that you can apply the term 'see' to them. They're obviously photosensitive, though. Most tend to grow toward the sun, which is fairly logical for organisms that run on photosynthesis.
  12. Jun 1, 2006 #11
    But is it (theoretically) possible for us, with our functioning visual cortex, to become visually aware of the blackness behind, below, above and besides our heads?

    I imagine this would look like 360 degree (both left/right and up/down) vision with a small section (that whats in front of us) being illuminated.
    Last edited: Jun 1, 2006
  13. Jun 3, 2006 #12


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    Well, there is no blackness behind our heads-- that was the point of my using that example. If you compare the visual experience of complete darkness to the visual experience of seeing out the back of your head, you should find that they are different, because the latter isn't a visual experience at all. You might think of it as analogous to the difference between the written numeral "0" as compared to the complete absence of any written number whatsoever. They may amount to roughly the same thing conceptually, but in one case there is a representational vehicle, a pointer which we interpret to mean "nothing," and in the other case there is literally nothing to begin with.

    I don't know whether or not a normally structured visual cortex could support a visual experience as of complete blackness, as if it were located in the experiential space behind one's head. Certainly if we remove the "normally structured" constraint, I imagine it would be quite possible. Some people claim to be able to experience 360 degree vision in lucid dreams, so it may be possible even for more or less normally structured human brains in the proper circumstances.
  14. Jun 5, 2006 #13
    When our pupils get smaller/larger, or our eyes get tired, our field of vision can also change in size. However we do not experience the removed parts at the edges of our field of vision as blackness - we simply dont experience it, just like at the back of our heads. So i imagine there must be some kind of filter in the brain that selects which 'black patches' we are aware of and which ones we arent (black patches here being an absence of light hitting our retinas).

    If i focus on the edges of my field of vision however, i can experience a little bit of blackness there. So it seems to me like this is just a matter of focussing hard enough.
  15. Jul 2, 2006 #14
    I read somewhere (but cannot cite the reference for I cannot remember where I read it) that blind people see black and white dots.

    I think it's safe to say that most of the posts on this thread (including mine) are speculation to some extent, and as someone says, until we ask someone who was born blind, but later acquired vision, we wouldn't know.
  16. Jul 3, 2006 #15
    I think the absence of anything on the back of our heads is only possible because we actually see at the front of our heads.

    Kind of like you can't have black without white.
  17. Aug 16, 2006 #16
    Being that the brian processes visual information a person who had blindness in the eye or optic nerve shoudl see blackness. A person whom is blind do too a malfunctioned brain should see nothing.
  18. Aug 17, 2006 #17
    I've thought about it. Actually, I figured that one should come to the conclusion, "no, they're blind," after thinking about it, and not before.

    People who are not thinking would try something that has nothing to do with being blind, like closing their eyelids. Closing your eyelids does not end your sensitivity to light and its absence, it only reduces the amount of light entering your eyes. When you reduce the light level, you are sensing the absence of light as blackness. Without sensitivity to light and its absence, you would not see blackness.

    So, before you ask the question again, why don't you please think about it. :shy:
    Last edited: Aug 17, 2006
  19. Feb 3, 2009 #18
    we percieve our universe with our sense organs. an absense of a sense organ cuts and avoids the existence of that universe. you cannot percieve the concept vision, with out a sense organ(call it optic nerve) or other stimulator. if you are told the situation of a person who do not have that sense, and you are not that type, then that will be only speculation and requires faith, you can not prove it. People who are not Blind can not tell the situation because they don't have the capability not to have vision.
    Even, if you ask a blind person with no vision, it will misled you, because he is going to use the terms that we agree, it is a belief for him, he don't know about it, because he don't have the senses(only faith). for those who do not have the sense of vision, vision and darkness is an imagination or concept that doesn't exist in thier universe, but are persuaded to believe that they exist. Faith is natural, the absense of a sense organ force you to believe in something. it is like believe in a spiritual body, because we do not have the sense organ to percieve them, we only accept and imagine.
  20. Feb 3, 2009 #19
    May I recommend an excellent book
    Eye and brain by R L Gregory
    I had this book years ago but I think a friend must have taken it on permanent loan.I seem to remember that the author addresses some of the issues being discussed here.
    Last edited: Feb 3, 2009
  21. Feb 22, 2009 #20
    i would rather consider it as not seeing at all

    its like the mind set we have when we close our eyes, not when we enter a dark room

    Are we continuously 'seeing' when we close our eyes? How about when we enter a dark room?
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