Is Sight a 3D Illusion Created by 2D Perception?

[ModusPwnd]

Lots of opinions here. I am firmly in the camp that we see in 2D, not 3D. Two 2D images does not make a 3D image. Furthermore, I do not think that a 2D image plus depth perception is equivalent to 3D. When we see in the x direction is an effective continum of information from left to right. That is 1D. We see an effective continum of information in the y direction from down to up, that is another dimension. To see in a third dimension we would need a continum of information in the z direction, front to back. Depth perception does not provide that. If we saw in 3D we would simultaneously see the front and backside of an object, as both the front and backside are part of that continum in the z direction. We can't do that. What we can do is take a series of 2D cross sections and then get a sense of the 3D structure. But I don't think people can even visulize 3D in their minds... what we do instead is visulalize a finite set of 2D cross sections or flay the 3D object out into a 2D image.

If 2D plus depth perception is 3D, then 1D plus depth perception is 2D? Nope, its not. A one dimensional image with information on the distance of each point does not make a two dimensional image. It makes a 1D cross section of a 2D image, and cross sections always lose a dimension.

 

[sophiecentaur]

Humans infer information about depth a number of ways, including the obscuring of far away objects by nearer ones, shadow, and the comparison of the images from both eyes. Depth perception is not destroyed when one eye is closed. Strictly speaking, both eyes report only two dimensional images; the brain constructs what we generously call a 3-dimensional representation much later in the visual stream. It would be a stretch to say that we "see in 3-dimensions".

I agree. People seem to think that all we perceive about the world is dominated by our binocular vision. That view is a naive as saying that the eye is 'like a camera' and leaving things at that. People with vision in only one eye and even people who have never had vision at all, can have excellent spatial perception*. We use countless clues about relative distances, sizes and even masses of objects. This is why we are relatively easily deceived by optical illusions and magicians. But those are exceptions and largely not 'natural'. A quick read through this Wiki article (despite the disclaimer at the top) should be enough to show something of what's really going on when we see a scene and retain it when we leave the room or close our eyes.
*None of us has ever seen the inside of our mouths in detail but, from the evidence that our tongue gives us, we have near perfect (3D) map of it and (mostly) can avoid chomping down on our cheeks and tongue, even during violent chewing of our favourite food.
It just ain't as simple as that!

 

[ZapperZ]

As has been hinted a few times on this thread, the OP seems to not know the difference between the human perception of 2D/3D versus the physical reality of something that is either 1D, 2D, 3D, etc...

Let's get this out of the way. If I confine an electron gas in 2D, the density of states of this electron gas looks VERY DIFFERENT than when it is in 3D. The same can be said when I compare a 1D electron gas versus 2D and 3D. Students in intro Solid State physics course are very familiar with this. This is an absolute physical property, and not a perception based on the human eyes/optics system.

Secondly, one must ask the question on why we see a 2D image from a regular photographs, but see a "3D" image from a hologram. In fact, try looking at the hologram (or go to a 3D movie) and close one eye. Do you still see the 3D effect, or at least see it as CLEARLY as when you had both eyes opened?

The problem with using what we see as a "detector", as has been stated already in this thread, is because our brain tends to "interfere" with our perception based on our experience and our evolutionary characteristics. It is why we have optical illusion, where our brain is inserting stuff into what we see even when it is not there. So the issue of 2D versus 3D observation with our eyes cannot simply be attributed to just optics or external physical properties.

As an experimentalist, I will again emphasize the fact that you must also pay attention to the device you are using to detect or measure!

Zz.

 

[arydberg]

You need to understand how a 3D camera works. It an best be understood by 2 cameras 2 1/2 inches apart. You take 2 pictures at once. The left picture is then presented to the left eye. The right picture is presented to the right eye. All the rest is the brain. With eyesight our two eyes perceive 2 slightly different pictures as they are also 2 1/2 inches apart and again the brain takes over. It is the tiny differences in these two images that give us 3D.