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Is it true you lose depth perception when looking out of one eye?

  1. Mar 11, 2007 #1
    I've heard this a lot - that you lose depth perception when looking out of only one eye. So I have to ask - is this true? When I try it everything looks exactly the same to me. :confused:
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  3. Mar 11, 2007 #2


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    Yes. Two eyes means binocular vision.

    If one uses one eye, the brain does try to compensate.

    Try covering one eye and, perhaps with the help of a friend, gauge the distance to an object. Or alone, close one eye and reach for something about 18 inches or 0.5 m away - and see the difference between using one eye and two.
  4. Mar 11, 2007 #3


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    Yes, if you're in a familiar surrounding, you already know where things are relative to one another, and can judge distance based on the apparent size of objects, because you already know their size, so your brain can compensate for the loss of visual information (you could navigate a familiar room fairly well with both eyes closed...blind people rely on this). Also, as you get closer to an object and move your head around to see different sides, you can compensate somewhat for lack of binocular vision.

    If you really want to test this, go to an unfamiliar location and try to judge distance. Or, sit in an empty room or open field (where you won't have other clues about distance), and have a friend place objects at different distances when you aren't looking, and then with one eye closed, see how well you can identify which is the closer or farther object. Or, close your eyes, have someone choose a distance to stand from you, then open only one eye and try to throw a ball to them (choose something soft so you don't hurt them when your aim is off).
  5. Mar 11, 2007 #4
    I can't do this with both eyes open either :uhh:

    I'll try this later (except for the throwing one, which I can't do with both eyes open either :rofl: )

    Thanks for the suggestions, although I still think everything looks the same. Are you supposed to be able to *see* a difference?
  6. Mar 11, 2007 #5
    you see depth with one eye since your memory can fill in the information. its impossible to tell the position is without two stationary sensors(i think it applies only for 2 dimension space, for 3 dimensions is take 3 sensors)

    ask a friend to hide his whole body behind an object, and only show his two fingers(at a small distance) when one is behind the other, and try to observe which finger is closer(try this for a couple of times, since its a 50-50 chance for each observation to be true) and then try it with two eyes, youll see the difference
  7. Mar 11, 2007 #6
    Classic example. Open both eyes.

    Now 'point' with your left and right hands. Hold your hands out infront of you and touch the tips of your 'pointing fingers'

    Now close one eye and see if you can do it, you cant.
  8. Mar 11, 2007 #7
    I am not 100% sure about this but this simple thought experiment may account for it a little bit. I don't know how the brain works... but this is one reason why it may work for two eyes but not for 1 (it definitely won't work for one)

    If you hold a pencil infront of your eyes and close one eye, and then take turns and close the other eye, you will notice that the two images that your eyes are recieving differ. In fact, the closer an object is, the more the two images differ (in respect to that object)... could this be how our brain judges depth? Maybe someone with a degree in biology can explain how it works. I would research into it but I can't right now.

    The reason that you can't judge depth with only one eye is blatant, there is nothing for the brain to compare with. Think about holding two unsharpened pencils, one quite a bit further from the other, but it is bigger (the viewer does not know this) and it is held in such a position that the sizes look the same. If they were being hovered in the air so that you couldn't use other factors to judge, wouldn't they look to be the same distance? But with two eyes your brain could use the two seperate images to compare them.
  9. Mar 11, 2007 #8


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    An easy test is to take a tennis ball and then with only one eye open, bounce the ball against a wall and catch it.
  10. Mar 11, 2007 #9
    well, it can be mathematically proven that in two dimensions, you may measure distance with two dot sized "angle sensors" placed in two points in space at a known distance between them. though i do not know if the brain uses the same way to calculate things(i believe not, since the eyes are very memory dependent, also the brain seem to prefer wacky ways to function, it never favored symmetry, unlike our contiuos mind)

    one sensor can not do such thing, if it could, how would it determine whether an object is closer, or bigger? heh, i think that if we were not able to determine if an object is closer or bigger, then we would not know what length is, we would only see space as angles, quite odd it would be...
    Last edited: Mar 11, 2007
  11. Mar 11, 2007 #10


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    Well, my Dad was practically blind on one eye, and he said he didn't have much depth perception. Dads are often right, at least about themselves.
  12. Mar 11, 2007 #11


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    The quickest, easiest test I know about is simply touching your fingers. Close 1 eye, bring your hands up from your sides and touch your forefingers together.
  13. Mar 11, 2007 #12


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    You don't need a degree in biology to explain this.

    Your two eyes are actually located in different places, a few inches apart.

    Of course the images look different; it's like taking two photographs of the same object from completely different places.
  14. Mar 11, 2007 #13


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    So what happens in people who have had Corpus callosotomy: the surgical disconnection of the two brain hemispheres by cutting the neurological bridge that connects both hemispheres. Depth perception must have been lost.

    Does anyone know of other everyday life things that these people are affected by?

    There's an experiment that you show an object to the person's left eye only, the person can then not name the object because the tasks are handled by different brain hemispheres (left vision in the right brain hemisphere, speech in the left brain hemisphere) and since the brain hemispheres don't communicate, the left brain does not know what is going on.
  15. Mar 11, 2007 #14

    True :rofl: , I made the post really quickly and didn't have much time to rethink my post. I was probably going to go on about something else but didn't. I wasn't pondering over why the images are different... if thats what you inferred somehow. I was not 100% sure whether this is the only tool the brain uses to judge distance, and was just pointing out that while my answer may be the common sense one, an expert may have a more complete explanation of some surprising sort. For example the amount that the lens of the eye has to change to bring an object into focus may also give hints as to the distance of an object.

    Yes, this was my point.. :smile: The brain could use the differences in the two images to judge relative distance, whereas one eye couldn't, and thats why you can't have depth perception with only one eye unless you are familiar with the objects. Unless there is some surprise of some sort.
    Last edited: Mar 11, 2007
  16. Mar 11, 2007 #15
    You only lose your depth perception if you hold your head still. If you move your head around it comes right back without having to open your other eye.

    The reason should be obvious from the descriptions already given.
  17. Mar 11, 2007 #16
    Strange fact: You loose depth perception when both of your eyes are closed.
  18. Mar 11, 2007 #17
    But your sonar goes way up!
  19. Mar 11, 2007 #18


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    I don't think that's necessarily true (but haven't looked into it either). The reason I don't think so is that the optic nerves cross before entering the brain, not after, so I don't think there's a need to have both sides of the brain connected for visual information to be correctly relayed.

    Correct. The same concept applies to direction finding with hearing as well. The slight difference in phase and intensity of the sound wave as it hits your eardrums on either side of your head provide information about which direction the sound is coming from. Though, now I'm going to have to ask someone in the sensory neuroscience group how we distinguish between something directly in front of us vs. directly behind us. :confused:
  20. Mar 11, 2007 #19


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    Are your eyes different strengths? If one eye is much weaker than the other, you won't have very good depth perception. You don't notice because you fall in the habit of relying on your better eye, but that's the sort of thing a thorough eye exam picks up.
  21. Mar 11, 2007 #20
    Nope, they're both equally poor (-10.0 in both eyes). I'm a really bad judger of distance, and I have little coordination which is why I sad those tests wouldn't work well for me.
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