Its actually because we have two separate eyes, so we see everything from two angles at once. You can test it, look at your hand all bent with one eye closed, then look at it with both. (obviously you'll know its a 3-D hand so it wont appear completely flat, but the depth will become more exaggerated with both eyes open)
We see in 2d. The mind interprets the data from both eyes to construct the illusion of 3d space. Check out info on brain sciences and in particular a phenomenon called 'blind sight'. By dr ramachandran made an interesting docu about this. In it he explains how we have visual conscious sight and a kind of unconscious sight that kind of compares the relative distances between moving objects to give us a sense of space as we move through it. (from an older part of the brain , evolutionarily speaking) there is a case of a man who has brain damage in the part of the brain that enables conscious vision but he can still effectively see as things move around in his field of vision. Very strange. Sight is not straight forwards. There are even people who can see perfectly but due to damage to areas of the brain can not tell you what the object they are viewing is.
I believe that is incorrect. If we see objects because of our minds, blind people would be able to see. Also I beileve the idea that people have an extra sensory "visual" perception when we dream is false as well. If this were true, then visionary artists like leonardo da vinci would not need to use or train on reference models. We all could easily draw especialy seasoned artists could draw anything they want by simply "picturing it in thier mind. I believe that dreams are a combination of language and emotional states/physical states, not visual input.
Notice no visionary phrophet ever produces images to prove they have "seen the future" this is because scam artists (my opinion) like nostradamus
The reason I believe your eyes see 3d has nothing to do with both your eyes either, but rather the fact that your eyes can do something computer monitors cannot. I believe you actually see multiple resolutions when you look at objects with your eyes, the detail increases depending on how close objecst are (better if closer unless your farsighted). This is why monitors are having problems producing 3d images because either A. They produce level monitor picture resolutions B. They use photos (in the case of non stereo real 3d monitors) that are not using multiple resolutions, they use a single resolution ratio. I also believe when you look at older films, etc from non hdtv camera produced sources, on an hdtv monitor your not actually looking at real hdtv, your looking at downsampled pictures, just like taking a digital recording of a scratchy record, you get a digitaly recorded scratchy record when you do this. If both your eyes were necessary to see 3d as stereo geeks want us to believe, when you close your eyes you wouldnt see depth, and we can all determine easily by closing one eye how far something is. I believe 3d photos and anaglyphs are actually increasing the pixel resolution by transparanting them over top of eachother wich helps prove a point. Also in 3d movies and films 3d images can be improved by filming in multiple resolutions rather than keeping a level static resolution as I believe objects closer to you for people with normal vision, actually increase thier resolution detail, something regular monitors and hdt and pictures do not do (they have static picture ratios of 600x800 etc, no increase or decrease of pixelation). Your eyes are capable of seeing incredibly fine pixel resolution and actually to the point of not seeing pixels when you view. How well you can see resolution and the curvature of your eyes.
When we look out across a field, how do we know one distant object is bigger than another, or that one is behind another? Why don't we see everything "flat", instead of in three dimensions, in proper relation to each other? The fact is that we see things not only with our eyes but with our minds as well.
We see things in the light of experience, And unless our mind can use the cues it has learned to interpret what we see, we can become very confused.
For instance, experience has given us an idea about the size of things. A man in a boat some distance from shore looks much smaller than a man on shore. But you do not say one is a very large man and the other a very small man.
What are some of the other "cues" your mind uses? One of them is perspective. Yon know that when you look down the railway tracks they seem to come together. So you consider the width of the tracks and get an idea about distance. Experience tells you that near objects look sharply defined and distant objects seem hazy.
From experience you have also learned how to "read" shadows. They give you cues to the shape and relationship of objects. Near objects often cover up parts of things that are farther away.
Moving the head will help you decide whether a tree or pole is farther away. Close one eye and move your head. The object farther away will seem to move with you. While nearer objects go the other way.
The combined action of both eyes working together also gives you important cues. As objects move nearer to you and you try to keep them in focus, your eyes converge and there is a strain on the eye muscles. This strain becomes a cue to distance.
