Comment by dan_mctree | Hacker News Reader

Comment by dan_mctree | Hacker News Reader

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I think you can't. The problem is that we don't actually see 3D, we basically see 2D twice. This gives our senses enough info to reconstruct a 3D mental image, but the information we gain isn't truly 3D.

Actual 3D-sight might include us seeing the inside of objects, what's behind them, etc.

We're aided in converting our 2x 2D sight into 3D mental models through the use of color and parallax. In projections on images, it's easy to just use color and get rid of parallax, and still get sort of close.

Suppose we tried to make a 3D projection of a 4D world, we don't actually get any significant new tools. We're still going to be limited by having to use parallax and color. This doesn't allow us to add enough information to add that 4D projection into 3D as neatly as the 3D into 2D works. At best you could try to distribute the information somehow. For example by giving information about the third dimension through brightness and the fourth dimension through hue. It certainly wouldn't work nearly as well though.

FWIW this is really not true. (The bit about stereo vision being required to see 3D.)

When I was in college I was fairly decent on the ping pong table, call it high amateur. I also have very very bad vision - -5 diopters in one eye and -6 in the other. At the time I wore contacts and I was also really really poor. At some point I lost one of my contacts and for six months I was effectively blind in one eye for the purposes of ping pong. It took me about a month, but fairly quickly I was playing at my old level without anything close to stereo vision.

Did you play with only one eye open, or just one contact lens? I have worse vision than you (-8.0, -7.50), and I know that I can still function with just one lens in of needed. You definitely still have stereo vision even if one input is blurred. Your brain does quite a bit of compensation, and I can imagine if you operated this way for months that your brain would be even better at assimilating the noisy information from your "bad" eye.

Sulam is basically correct. I was born with strabismus (my eyes don't focus on the same point). To avoid perpetual double vision, my brain compensates by basically only using one eye at a time. It switches automatically when I'm looking to the side, and I can also switch consciously. (My color perception is very slightly different in each eye, it's weird.)

It turns out that stereovision is the least important of several depth cues humans use, and is only really effective out maybe 10 feet or so--beyond that the parallax is too small to give much useful info, and we rely on apparent size, relative motion, surrounding context, etc. I can catch a ball just fine, as an adult.

It's really only an issue within arm's reach, and then only when I'm distracted. Occasionally I'll reach for something without paying attention and miss by, like, a foot. Also, I can't use 3D glasses. (With the new polarized kind I can at least wear them and see a normal 2D movie. With the old red/blue kind, everything would be either red or blue, depending on which eye I was using.)

It isn’t just depth perception that is improved with binocular vision, there is binocular summation, which helps improve acuity. Two is better than one. However as you say, stereopsis seems to be one of the least important parts of sight.

You might have an advantage with not being able to watch some 3D movies - you can tell your friends/family that a medical condition prevents you going to them.

https://en.m.wikipedia.org/wiki/Stereopsis

https://en.m.wikipedia.org/wiki/Binocular_summation

> (My color perception is very slightly different in each eye, it's weird.)

I have comparatively uninteresting/normal vision (biggest issue shortsightedness) but I have this too. My left eye sees more blue, my right eye more red. Looks like the cone distribution wasn't perfect.

I'm not sure, but I think the sun's rays don't have much of a blue component: my left eye gets fractionally less sore from bright sunlight, so if it's really bright out I'll generally be closing my right eye.

The sun emits black body radiation with a 5800K temperature, which means its emissions peaks at yellow-greenish, but it still emits around 90% of blue compared to green

How about compared to red? That might suggest whether exikyut's experience (red-seeing eye more light-sensitive than blue-seeing eye) is coincidence or related.

I was trying to make the same point, I think? I was just trying to note that I have done the single contact lens thing as well, and even after just a few hours, your brain starts compensating for it.

I played with one contact, and if you have vision as bad as mine you know there is essentially no chance that I would be able to build a stereo image of the ball with one eye uncorrected. I know this because I had to relearn how to play, and I found myself using other cues for depth, like what the ball was occluding.

I crushed my glasses with my butt once, and went without for a year or so until I could get new ones.

Once I got the new glasses I was astonished at how flat and "PlayStation-like" everything looked. My depth perception was thrown off and everything looked much closer to me than it actually was.

I think my brain was using blurriness as an indicator of depth, in addition to binocular vision, and with my myopia corrected it lost that information and had to readjust to relying primarily on binocular vision to gauge depth.

i would argue that we don't see in any dimension, at least in terms of the physical capacity of the eye. we just take in varying wavelengths of light and those have no intrinsic dimensionality to them per se. the actual manifestation of dimensionality is, at least in my opinion, merely a construct of the brain. while I think it's accurate to represent reality as a multidimensional thing mathematically and formally, i don't know if dimensionality is an intrinsic feature of it or just a way of categorizing our concept and experience of it. either way, the fact of the matter is that the eye merely takes in raw photons and passing messages on to the brain based on the frequency and intensity of the light, and after saying that i suppose i would be willing to admit that the core nature of light and waves in general is two dimensional, since a wave is defined in terms of frequency and amplitude.

> The problem is that we don't actually see 3D, we basically see 2D twice.

Most of us do. But people who only have sight in one eye have no difficulty perceiving three dimensions. And some fairly large percentage of people with binocular vision are stereoblind, typically without even realizing it.

If anything, I'd say it's not that

> We're aided in converting our 2x 2D sight into 3D mental models through the use of color and parallax.

so much as that we're aided in converting our 2D sight into 3D mental models through the use of stuff like color and parallax through the use of stereopsis.

As you mention, binocular vision is lacking in a surprising number of people and until recently this was thought to be uncorrectable if not treated while the child was still young. That turned out to be not entirely accurate.

Those without binocular vision can have a fairly large range of non-specific symptoms and perception problems. There is an interesting discussion of the change in understanding in this link. http://www.strabismus.org/all_about_strabismus.html

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