Thread: Why do Distant Objects Appear Smaller?

Is it the curvature of the eye lens? If so how then does it work?

If our eye lens was flat and not curved, then would we be able to see in 3D, would we have depth perception?

Do all animals have depth perception? If not, then how do they view the world compared to us?

It's simple geometry and intercept angle against the sphere of your vision. Nothing to do with refraction, curvature or anything else.

And that simple geometry is used by the human brain to estimate distance to the far away object.

I read that we see in 3D primarily because our eyes are apart from one another, 2 slightly different inputs and thus the brain interprets what we see in 3 dimensions. Can't help but notice that fish have an eye on each side of their head and I'm wondering if they also see in 3D?

>I read that we see in 3D primarily because our eyes are apart from one another, 2 slightly different inputs and thus the brain interprets what we see in 3 dimensions.

That's only about one of a dozen ways we perceive distance. (Keep in mind that one-eyed people seem to do just fine at things like walking, driving etc.)

A quote from a Neuro Optometric Rehabilitation Association (NORA) article:

Schein writes, "Individuals limited by loss of vision in one eye have difficulties in depth perception." "Determining the distance within three feet from the eye is extremely difficult and highly unreliable." "Beyond three feet, other distance cues can substitute for loss of binocular disparity, provided monocularly impaired individuals are free to move their heads, which allows them to obtain information about relative distances by taking more time than they would when visual images from both eyes can be superimposed, as they are with binocular vision." "Mishaps can occur when monocularly impaired persons are in heavy traffic unless the head is constantly moving from side to side to increase the visual field".

Seems that depth and distances are affected when one loses an eye.

Does the brain fake 3D because a one eyed person actually sees the world in 2D?

Originally Posted by zinjanthropos

Seems that depth and distances are affected when one loses an eye.

Definitely. But since they only lose one of the many methods of measuring distances, they are still able to perceive distances. (Parallax distance perception, which is what you are talking about, doesn't work past about 5 feet anyway - so beyond 5 feet having two eyes doesn't give you a significant advantage.)

Does the brain fake 3D because a one eyed person actually sees the world in 2D?

No, they actually see in 3D. Just like two eyed people.

Originally Posted by billvon

Originally Posted by zinjanthropos

Seems that depth and distances are affected when one loses an eye.

Definitely. But since they only lose one of the many methods of measuring distances, they are still able to perceive distances. (Parallax distance perception, which is what you are talking about, doesn't work past about 5 feet anyway - so beyond 5 feet having two eyes doesn't give you a significant advantage.)

Does the brain fake 3D because a one eyed person actually sees the world in 2D?

No, they actually see in 3D. Just like two eyed people.

Because I never bothered to think of this before and the fact that I don't know a whole hell of a lot about vision, I get confused when you write what you said and then I see an article from Scientific American like this.

Originally Posted by skeptic

And that simple geometry is used by the human brain to estimate distance to the far away object.

Specifically, the tangent.

The angle thus created is called the subtended angle. At small angles, tan(Φ) ≈ Φ.

I read that human depth perception beyond about 50 feet depends on the apparent size of an object compared to its known/estimated size; that is, using the subtended angle. Closer than 50 feet, the two eyes see different pictures, and distance is computed based on the parallax sensed; that is, binocular vision.

A one-eyed person can sense distances closer than 50 feet from the subtended angle and from small movements of the head (a sort of temporal parallax) similar to the way we sense the distance of stars from images taken at different points in our orbit around the Sun. .

Reminded me of this:

Father Ted: 'Small' vs 'Far Away' - YouTube

Originally Posted by zinjanthropos

Because I never bothered to think of this before and the fact that I don't know a whole hell of a lot about vision, I get confused when you write what you said and then I see an article from Scientific American like this.

That was exactly the article I was going to look for to point out that full stereoscopic vision requires two eyes. I love her description of the pleasure of seeing snow flakes ... something it is so easy to take for granted.

The reason for objects appearing small in the distance, is directly related to
physics, the study of physical objects and their relationships which include light.

The eye is a crude receptor for emf, electromagnetic radiation. It can only precieve the wavelengths of light.
With two of them spaced at a distance, it allows for triangulation, forms a triangle, and allows for measurement of position.

Light propagates and disperses in accordance with the square of the distance.
The light coming from an object at a distance is subject to all the properties of light.

It would then be inferred that the object appears smaller because, it's size is reduced according to the inverse principal.
The preception of the object appears to be subject to the properties of the medium in which it is conveyed.