The human body is reflectively symmetrical down the vertical Y axis, so our eyes are on the horizontal X plane. We need two eyes to process three dimensional space, but does placement matter? What if our eyes were vertically aligned instead?
I’m trying to imagine what benefits there are to our current arrangement, and I can’t think of anything that is inherently reliant on it. However, I may be missing something. Perhaps the orientation of the horizon and that 90% of our waking days involves the X and Z planes?
One big benefit is out peripheral vision. Horizontally placed eyes allow us to see farther to our right and left without turning out head, which is useful when you’re a tasty morsel to a lion.
We have a middle-of-the-pack eye alignment, with pretty wide peripheral vision and pretty good forward vision. Binocular vision - Wikipedia
If they were vertically aligned (say above and below our nose), we wouldn’t be able to see to our peripheries as much. Humans don’t typically encounter much danger from above, though it’s interesting that rodents and such do and still never managed to evolve upward-looking eyes.
This brings to mind the age old question of why, when you look in a mirror, your right and left hands are reversed, but your head and feet are not. If your eyes were vertically positioned, would your mirror reflection be upside down?
No. As GuanoLad says, mirrors neither reverse right and left nor top and bottom; what they reverse is front and back. We consider this to be reversal of right and left instead because we imagine rotating ourselves 180 degrees around the axis from top to bottom to assume the position seen in the mirror [thus turning front-back reversal into left-right reversal], rather than imagining, say, rotating ourselves 180 degrees around the axis from left to right [thus turning front-back reversal into top-bottom reversal]. But our eye placement upon the face has nothing to do with this being our common imagination; it’s a matter of gravity making the one motion more conventional than the other. (Similarly, with writing on paper, or other such things… we typically imagine rotating objects with the top and bottom maintained while the other dimensions reverse, rather than rotating them with the left and right maintained while the other dimensions reverse, again largely because of gravity [which defines “top” and “bottom” for us in the first place])
(Perhaps, though, if we had eyes on two opposite sides of our head, and indeed failed to care so much about distinguishing the face from the back more generally, we would not commonly bother imagining ourselves undergoing any rotation to assume the position seen in the mirror in the first place, and think directly in terms of the reversal perpendicular to the mirror’s surface instead.)
The best way to understand this is by thinking about what actually happens: Particles of light reflect off you, take the shortest path to the mirror, reflect off the mirror, and take the shortest path to your eyes. Therefore, the reflection of your right hand is closer to your physical right hand than it is to your physical left hand, and vice-versa.
All this talk of flipping is a distraction. Nothing is flipped. Things are simpler than you imagine. You can only understand the world if you’re willing to let go of your common sense and let the facts guide you.
Imagine writing a message on a transparent sheet of celluloid. Now stand in front of a mirror, and hold the celluloid up so you can read it normally.
Now turn the celluloid around and show it to the mirror. Look at the mirror image, and note that it is backward, just as you would expect, just like when you hold a book up to the looking-glass like Alice did.
But wait! Since the celluloid is transparent, you can see the message there by looking directly at it! And what do you see? Looking directly at the celluloid, it is backward! Now look at the mirror. It’s backward too. So what you see directly in the celluloid is exactly what you see in the mirror. It’s not backward at all!
Well, I mean, it is backward in the mirror, but it’s backward when you look directly at (the back side of) the celluloid too. So they’re exactly the same! The fact of looking at it in the mirror isn’t reversing anything, nohow.
So why does the text read backward – both in the mirror and looking directly at the celluloid? It got that way when you turned the celluloid around to show it to the mirror! – That’s what reversed it left-to-right!
Unless, of course, you turned the celluloid around to show it to the mirror by flipping it top-for-bottom. Then it’s reversed top-to-bottom. (Try it!) But not because the mirror is doing it. It’s because you actually did flip the celluloid over that way.
(ETA: So much for the OP’s original question, I guess.)
Unless you have the power of flight, you live in a two-dimensional, X-Y world… front and back, left and right. Up and down are theoretical only, since a primitive proto-human cannot move in that dimension. Hence, it is more useful to see broadly in a horizontal plane rather than a vertical plane.
Maybe, but I think the fact that our eyes are paired horizontally has more to do with the way that other external organs, like legs, hands, ears, nostrils etc. are also horizontally paired. A bilaterally symmetric body plan is very basic to the structure of most types of animal, and very evolutionary ancient. Not only all vertebrates, but also flatworm, arthropods, annelids and most molluscs are bilaterally symmetric.
How could that work?* You could get binocular depth from either horizontally or vertically paired eyes, but in order to get 3D pictures that will work for humans, the lens arrangement on your camera has to match how human eyes actually are.
*Unless you turned the image pair 90º afterwards, but what then is the point?
They translate it to a 3D map in the computer eventually, I think. The final product was a 3D sculpture, not 2 pictures meant for the left and right eyes.
Particles of light take all paths, not the shortest one. The ones that reach your eye are the ones that took the only path that could reach your eye from you, reflecting off the mirror at the angle of incidence. This path is the not the shortest path, nor the only path. It just happens to be the one that your eye sees.
Vertical alignment would make sense if you have to take more than one photo, from different locations around the sculpture. You’ll get diversity of the views in the horizontal plane from the different photos. Each top-bottom pair will get you some vertical diversity. If the lenses were side-by-side, all your images would be in the same plane. That’s a guess, but if I were designing the system, that’s what I would do.
Hmm I always remember them as taking only one photo. For a 3D thing you’d want detail in every direction, so I don’t think the orientation of the lenses matters. Come to think of it, it may have been a Kinect-style 3D scanner, not a camera.
That, and the fact that humans are very close to being bilaterally symmetric (especially externally), and so an inversion of a human looks very much like a human.
How could that work?* You could get binocular depth from either horizontally or vertically paired eyes, but in order to get 3D pictures that will work for humans, the lens arrangement on your camera has to match how human eyes actually are.