B What is the True Dimension of Human Perception?

[ErenJaeger2]

I have read things saying humans see 2d and also things saying its more like "two and a half d" but that humans don't actually see in three dimension. But when you explain the spatial dimension, you start with the first which can be explained by a line. So anything living in 1d would only be able to move along that line.
Then 2d where you can visualise this as a plane, and finally 3d where you have basically have infinite layers of 2 dimensional planes stacked on top of each other which gives rise to depth. Humans obviously do see depth, so we do actually see in 3 dimensions don't we?

 

[Nugatory]

I have read things saying humans see 2d and also things saying..."

You will get much better and more helpful answers if you tell us where you read that.

Humans obviously do see depth, so we do actually see in 3 dimensions don't we?

In depends on what you mean by "see in three dimensions." A photograph is clearly a flat two-dimensional image, but our brains are generally pretty good at reconstructing depth information from the sizes, shapes, and angles we see in this two dimensional image. It's not surprising that we can do this, because the retina of the eye is also pretty much a flat two-dimensional surface, so the input to the brain has to be a two-dimensional image from which the brain must reconstruct the depth information. (We have two eyes, so the brain actually gets two two-dimensional images from slightly different perspectives - google for "stereopticon" to see how this helps construct the depth information). Artists have been taking advantage of this capability ever since the discovery of perspective drawing about 500 years ago - and also using it to trick our brains, as in some of M. C. Escher's more clever drawings.

So we do "see" 2D or "see" 3D? It depends on whether you're talking about what the eye delivers to the brain, or what the brain does with it.

 

[ErenJaeger2]

You will get much better and more helpful answers if you tell us where you read that.
In depends on what you mean by "see in three dimensions." A photograph is clearly a flat two-dimensional image, but our brains are generally pretty good at reconstructing depth information from the sizes, shapes, and angles we see in this two dimensional image. It's not surprising that we can do this, because the retina of the eye is also pretty much a flat two-dimensional surface, so the input to the brain has to be a two-dimensional image from which the brain must reconstruct the depth information. (We have two eyes, so the brain actually gets two two-dimensional images from slightly different perspectives - google for "stereopticon" to see how this helps construct the depth information). Artists have been taking advantage of this capability ever since the discovery of perspective drawing about 500 years ago - and also using it to trick our brains, as in some of M. C. Escher's more clever drawings.

So we do "see" 2D or "see" 3D? It depends on whether you're talking about what the eye delivers to the brain, or what the brain does with it.

So basically we do see in two-dimensions, since anything we see in everyday life could easily be shown in a picture. For example, say you're looking at a box sitting on some surface. This same image could be put in front of you as some sort of blown up photograph of the real thing and essentially you would see the exact same thing, assuming the picture is detailed enough. So anything we see in everyday life could be shown in a picture where we would still get the perception of depth. What would the argument for seeing in 3d be then? Because even if your brain is constructing this 3-dimensional image, you still only SEE that image in two dimensions and the geometry of what you're looking at will define how close or far something looks right?

 

[Nugatory]

So basically we do see in two-dimensions... right?

You could say that, and you wouldn't be wrong. But you wouldn't exactly be right either, because that's not really a good way of thinking about it.

We start with a three-dimensional scene somewhere in front of us. We bounce light off of it, some of this reflected light makes it to our eyes, the lenses of the eyes do complicated stuff to focus the light on the retina, cells on the surface of the two retinas of the two eyes respond to different wavelengths of light in various complicated non-linear ways, eventually these trigger signals in the two optic nerves, these signals arrive at the visual cortex where all sorts of additional processing happens, and eventually we end up sensing that there's something in front of us and some parts of it are farther away from us than other parts. That's a lot of complicated steps and it's not at all clear which of them is the one where we're "seeing" something. Thus, the question "Do we see in 2D or 3D?" isn't clearly defined and could reasonably be answered either way, depending on what you mean by "see".

Once your realize that this isn't a simple question with short and easy answers, you'll also realize that it is completely fascinating. One book that you might try is "Consciousness Explained" by Daniel Dennett, although it is not an easy read.

 

[sophiecentaur]

Bearing in mind the way our memory works and how we learn and recall the images of the world that we have in our head, it is a massive risk to try to impose any simple model of the system. Of course we 'see' in 3D and that doesn't have to involve our eyes / optic system at all. Totally blind people can carry a very accurate model of the spaces they occupy and, of course, we all have intimate knowledge of the spatial arrangement in our mouths, based on what our tongue tells us without ever looking. In fact, what we see in a mirror, when we peer (visually) into our mouths is pretty much an alien and surprising world.
A static image on our retina can only tell us about the nearest object in any direction but we are far too sophisticated to rely on that sort of snapshot of the world around us. I think that too much emphasis is put on Binocular Vision in the explanation of our visual perception. I know many people who can see with only one eye and I also have two friends with two perfectly functioning eyes who have no binocular vision as such (confirmed by their medics).
My opinion about having two eyes / ears and a few other things is that they are provided in pairs to improve greatly the possibility of survival in the even of one organ being damaged. Binocular vision is something that a clever, opportunist brain has made good use of. There are many grazing animals with very little overlap of fields of their two eyes but they cope with a 3D world very well yet have the benefit of almost 360° vision. (Optimised for their lifestyle as 'prey'.)