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Medical Binocular vision

  1. May 13, 2010 #1
    Hello everyone,

    If we have 2 eyes how come we don't see 2 objects. Then I found the answer was binocular vision, and both eyes concentrate on the same spot. Now my question is does the brain make the 2 different angles into one object or it always happens? I mean does something have to be done from the brain to merge these 2 views? Also I would like to know more about how the different view merge. Thanks :smile:
     
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  3. May 13, 2010 #2

    rcgldr

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    Except for a small point that both eyes are aimed at, your eyes see two slightly different images, which your brain interprets as a single 3d image.
     
  4. May 14, 2010 #3

    Moonbear

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    The images you view are processed within the brain to result in a 3-D image. Visual processing primarily occurs within the lateral geniculate bodies of the brain. There are layers within these brain nuclei that correspond to areas on the retina to process visual information from various parts of the visual field.

    Part of binocular vision is that information from only the medial half of the retina crosses within the optic chiasm to the opposite side of the brain. So, for example, on the right side of the brain, information from the temporal side of the retina of the right eye and the nasal side of the retina of the left eye is received.

    There's more processing beyond that. The information from the LGN is then sent to the occipital lobe for further visual processing. This is just the visual part of that pathway...there are other pathways for things like light sensation for circadian rhythms.
     
  5. May 14, 2010 #4
    Hey Thanks Moonbear :smile: I haven't learned any physiology about the eye. Just the basics. So from what you are saying. If there is an object infront of us. Does one eye cover one half of the object and the other does the other half. Then if we only look at an object with one eye, how come we see a full image, not a half image. How is depth processed when merging the two pics. Thanks :smile:
     
  6. May 14, 2010 #5

    Moonbear

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    Nope. If an object is directly in front of you, both eyes see it, but in a different part of the retina (dead center in front of you would mean the lateral parts of the retina of each eye detects the object...remember that the cornea is the refractive surface of the eye, and the lens fine tunes that information, so visual information is projected to the opposite side of the retina from the visual field). Then, the signal from the retina is sent to the brain via the retino-genicular-calcarine pathway and the brain processes the information about where the "picture" came from into a 3-D image. HOW the brain does this processing, I don't know, and is something people studying this field are still working on.
     
  7. May 14, 2010 #6
    Thanks again :smile:

    This paragraph is little bit confusing for me. So even if both eyes recieve the full image, is it only the information from one side (temporal or nasal) sent to the brain, so it can process the image. When looking from one eye is the whole image processed to the brain. Thanks :smile:

    Edit: Oh wait I think I undertand. Both images are processed but medial sides add up etc like this diagram.

    [PLAIN]http://www.99main.com/~charlief/eye3.gif [Broken]

    Then my question is for this to work why does both eyes have to look at the same spot. Is it easier to merge the pic this way, is this how the brain functions?
     
    Last edited by a moderator: May 4, 2017
  8. May 14, 2010 #7

    Moonbear

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    Information from both eyes is sent to the brain. The brain then processes what part of each retina the image came from to determine how to interpret that image into a 3D image with depth perception (if you close one eye, or lose vision in one eye, you still see the whole image of whatever is in front of you, but you lose depth perception).
     
  9. May 14, 2010 #8

    apeiron

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    Actually the LGN are thalamic relay structures and the action really takes place in the cortex.

    It is correct to stress the fact that the hemi fields of each eye are mapped to the same sides of the brain. So in the primary visual cortex, the information from the same part of the visual field captured by either eye ends up in the one place and not on opposite sides of the brain.

    Then the story gets complicated. The fusion of the image and extraction of stereoscopic information happens as the result of a hierarchy of visual processing (there are at least half a dozen tiers of processing).

    Also note that depth perception relies on more than just binocular cues.
    http://en.wikipedia.org/wiki/Depth_perception

    Which is why closing one eye does not suddenly flatten the world to 2D. We have learnt what things should be interpreted as far off and what is near too. If we get confused about that (as in various visual illusions) then no amount of accurate steroscopic information makes any difference to our reading of the situation.
    http://en.wikipedia.org/wiki/Ames_room

    More evidence that the fusing of the information from our two eyes is surprisingly high level and attention directed comes from necker cube and binocular rivaly experiments.
    http://en.wikipedia.org/wiki/Neural_correlates_of_consciousness

    Of course, you can still get double vision if your eyes fail to converge. So it is still also important to fuse the visual image right at the start of things by getting the eyeballs aligned.
    http://en.wikipedia.org/wiki/Diplopia

    But double vision shows that the cortex can both ignore conflicting information (as with binocular rivalry) and actually experience a pair of images simultaneously (if not with real clarity). There is a great plasticity in the "processing".
     
  10. May 23, 2010 #9

    sophiecentaur

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    People with one eye still have a good three dimensional appreciation of a scene and even people with 'perfect' binocular vision wouldn't get much stereo information for distant scenes. I think the whole binocular thing is over egged, in fact, because stereoscopic pictures work well for some people and can be impressive.
    I could be controversial and suggest that we have two eyes because having a 'spare' is such an advantage (and we have pairs of lots of things). As predators, we need forward facing eyes and that, in many cases, it is almost a nuisance to have to deal with two images and a lot of processing has to take place in order to reconcile conflicting images. Yes, we turn it to our advantage - evolution is not that dumb - but the fact that people with only one serviceable eye can have excellent spatial awareness and even good game skills suggests to me that binocular vision may be less of an 'advantage' than it is made out to be.
     
  11. May 23, 2010 #10
    Binocular vision is key to rangefinding, which is why predators have forward facing eyes. There is a snake, which I no longer recall the name of, which has evolved binocular vision for just this reason. Yes, the brain can interpolate a lot based on one eye, but it is no substitute for binocular rangefinding. Why do you think a Chameleon uses its eyes to search in two visual fields, but when it is ready to deploy the tongue, it focuses both in a binocular fashion?
     
  12. May 24, 2010 #11

    sophiecentaur

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    I think you may be falling into the trap of attributing 'purpose' to the development of characteristics. We could also have an interesting conversation about why giraffes have long necks (it could be so that they can reach the ground without kneeling down).

    If you are looking at the relative survival advantages in having two eyes then I could be mischievous and suggest that there is far more advantage in having a spare eye than in having binocular vision. Lose a single eye and you're dead but lose one of two and you can survive for some time - extremely well, if you happen to be a human.

    As for the chameleon, you could say that binocular vision is better (particularly at very close range), so why should the animal not use it?

    I have not be saying that binocular vision is a waste of time. Far from it. In circumstances where it works, it is clearly an advantage but my point is that it may not be as vital as people make it out to be. I have spent some time looking for links on the net which could actually quantify the depth resolution for 'normal' human vision and can't find anything more than 'arm waving' assertions about it. Yes, the mechanism is described and so is the way the brain processes the signals. But how much of this is merely to resolve two contradictory images?
    Things may not be as obvious as they seem with binocular vision. We need more than two views, perhaps. :wink:
     
  13. May 24, 2010 #12

    apeiron

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    Isn't this falling into the trap of attributing purpose to traits?

    But anyway, the less controversial reason for pairs of things would be bilateral symmetry - it is an easier way to build complex bodies.

    And as IceEcliptic says, predators favour binocular vision for a reason. The correlation exists in animals from hawks, to snapping turtles, to T.rex. It is also characteristic of animals that live in cluttered environments like leafy forests. So the presumption that two eyes is better than one for depth perception seems safe.
     
  14. May 24, 2010 #13

    sophiecentaur

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    I'm not attributing a Purpose. I'm merely pointing our a survival advantage of certain traits.

    Also, I never said there was no advantage in binocular vision. I was just putting it in proportion. And I don't think there can be an argument as to whether losing one of two or losing one of one is the greater disadvantage.

    Furthermore, if you have two eyes, anyway, you might as well maximise the information you get from them by processing the information. And there are many humans with very little use of one eye who, as I said before, do pretty well without the other.
    Some of them can even manage to run the country / economy for a while!

    There's always a risk of post hoc rationalisation where evolution is concerned. Correlation is not cause, remember.
    And how about that giraffe thing, too?
     
  15. May 24, 2010 #14

    apeiron

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    There is just no logic in your responses. An argument for having two eyes has nothing to do with an argument for binocular vision.

    If we just had two eyes because we need a spare, then why would we "waste" them by having both on the same side of the head? There must instead be some evolutionary advantage. And improved depth perception is the standard explanation backed up by plenty of research.

    If you can suggest some better reason for overlapping eyes, rather than just for spare eyes, then sure, let's hear it.
     
  16. May 24, 2010 #15
    I would add, that in the absence of modern medicine, losing an eye to infection or trauma would be likely to endanger your survival. Having a viable spare you are unlikely to survive to enjoy makes no sense. Glaucoma, macular degeneration, tend to occur in both eyes, not one.

    We are sight-oriented bipeds, who rely on depth-perception a great deal. As cursorial hunters who gained an advantage by stabbing and hurling weapons (which took lot of effort to make) there is a good argument for binocular vision. Before that, why do monkeys and apes have bioc? Hint: it helps when you need to gauge a jump in trees.
     
  17. May 24, 2010 #16

    tiny-tim

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    Don't all mammals have binocular vision? :confused:
     
  18. May 24, 2010 #17

    sophiecentaur

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    So having no vision at all because you lost your only eye is not any worse than losing one of two? Come on. Close one eye for a while and try walking around - then close both eyes.

    I wish you guys would read what I actually have been saying. Binocular vision is very very useful but not as essential as having some vision at all. Also, there are many humans who do not have functioning binocular vision. People without it are unlikely to broadcast the fact - and may not even be aware of their lack - they may not be impressed by 3D films as much.

    Did we evolve 2 eyes so that we could use binocular vision or did we develop binocular vision to maximise the usefulness of the information from two eyes? It's only an advantage to do it that way for predators - all round vision is a bigger advantage for prey. That's two separate uses for two eyes.

    And, seriously, has anyone any objective data about the actual spatial information that binocular vision gives? I can find nothing, which is one reason why I am suspicious of just how useful it really is. Compare that lack of data with the detailed work on acuity and colourimetry which is quoted all over the place and can be repeated easily. Some facts would reduce my objections immediately.
     
  19. May 24, 2010 #18

    apeiron

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    The question was about the evolutionary advantage of binocular vision and depth perception. If you want to talk instead about the evolutionary advantage of two eyes in the first place, then that is a different discussion.

    And as I said, I would think the answer to that is more about development than evolution. Brain structures have bilateral symmetry because this is a developmentally simple way of breaking the symmetry of a neural tube.

    For example: http://media.caltech.edu/press_releases/13182 [Broken]

    Or if you mean not evolutionary advantage studies but the basic psychophysics, then the classical reference is of course: http://www.sciencemag.org/cgi/content/short/145/3630/356
     
    Last edited by a moderator: May 4, 2017
  20. May 24, 2010 #19
    Nope, think of some prey animals, deer for instance. They may have some slight convergence, but they don't use their eyes in concert to focus in the center of a visual field. They don't need to rangefind grasses, they need to see binocular predators coming from a wide field!
     
  21. May 24, 2010 #20
    In bold, I do not think that can be emphasized enough, as the way that binocular vision could ever enter the fray to begin with.
     
    Last edited by a moderator: May 4, 2017
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