How does 3D vision work with one eye compared to two eyes?

god0fgod: How does 3D vision work with one eye compared to two eyes?
I’ve read that the brain can calculate 3D by taking two images from two eyes and comparing them. However, 3D works perfectly fine with one eye. Surely this “Binocular vision” is pointless if the brain can calculate 3D perfectly fine with one eye.

Does the brain just guess or is there some other trick involved? I notice eyes individually focus. So the brain could calculate the amount of blur and work out the distance that way?


🙂 carrotstien
Hello. Good question.
Our main method of determining optical depth is parallax. Each eye sees the world from a slightly different angle (as you know). If you close one eye, your ability to perceive depth is severely diminished. Try to play catch with a soft object with one eye closed – you should find it quite difficult.
Of course, as you have realized, it is not impossible to perceive “3d” using one eye. However, this is due to shortcuts we learn throughout our lives. We know rules like shadows, overlapping, angular motion during motion, focus, memory of size, etc.
However, these are all very negligible with respect to depth perception compared to parallax.
This is exactly how optical illusions like these two work:
dragon head:
taller twin illusion:

Using focus sensitivity to determine depth isn’t a valid method – while being better than the stuff mentioned above, it still much worse than parallax. The reason is that parallax is more or less linear. Something twice as far away, will split off twice as far apart when looking at something nearer. However, the blur when using one eye, doesn’t change linearly – in fact, just looking at something blurry, won’t give you a hint at how far it is other than letting you know which very general area it is in. Something twice as far, while looking at a close object, will not seem to be twice as blurry – that is the problem.
Again, this doesn’t mean that people with one eye will live horrible lives. It just means that they will not be baseball players 🙂
My grandmother, who lost vision in one eye, is fine, and has become accustomed to the situation. However, while it already stopped bothering her, I still see her sometimes grab for thin air when reaching for something.

What do you think? Answer below!

  1. David E said:

    Here is some evidence that binocular vision is not pointless. Every predator has both eyes on the front of its head relatively close together to maximize stereopsis. Most animals likely to be prey have their eyes widely spaced or even on the sides of their head for the widest possible field of view.

  2. kdawg said:

    You don’t have stereo vision if you look with only one eye – but you can perceive the depth of things – but different methods like the way things move relative to each other and their size.

    With two eyes you are right that it is the slightly different images that allow your brain to perceive the depth.

  3. william said:

    Binocular vision takes place in the brain by superimposing two slightly different images from the two eyes. The further apart the two eyes are the greater the 3D effect will be.

    Monocular 3D is a misnomer because it’s only simulated 3D. By using different clues we can get an idea where objects are in relation to one another producing an inferior 3D effect. Some of these clues are:

    1. image size where the smaller image is assumed to be further away than the larger image.

    2. super imposition where it is assumed that if one image is partially blocking another it must be closer.

    3. look at an image and move the head back and forth. If another image moves in the opposite direction it is closer than the image you are looking at. If it moves in the same direction as your head it is further away.

    To see which type of 3D is better, compare depth perception with both eyes open. Then block off one of the eyes to see the difference for yourself. You’ll find that two eyes are much better than one when it comes to 3D.

  4. jonjac said:

    In Optometry school we learned about 27 clues to depth perception.

    Only one of these is binocularity.

    Hold your hand over one eye. Are you confused about depth?

    Binocularity helps depth perception at near distances only.

    Binocularity is limited by acuity.

    Stop reading physiology books.

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