What's it like to have two eyes? In other words, can someone give an explanation or offer a resource that could help me see (pardon the pun) what it's like to have stereoscopic vision?

July 16, 2012 10:27 AM

What's it like to have two eyes? In other words, can someone give an explanation or offer a resource that could help me see (pardon the pun) what it's like to have stereoscopic vision?

I lost my eye when I was very young--something like 4 or 5--and have been living with the one eye that I have quite fine. Sure there have been some problems reading and keep my eye moving smoothly along the page. Still, I'm curious as to what it's like to have stereoscopic vision? Can anyone give me a good description of it? For example, what does it mean to not have depth perception? I mean I can tell whether something is farther away from me than something else but I don't really understand what it means to have the kind of depth perception that two-eyed people have.

Any testimonials from people who lost the use of one of their eyes later on in life would be helpful as well.

Thanks in advance.

posted by RapcityinBlue to health & fitness (29 answers total)

The best 3d simulation in 2d I've seen is wiggle stereoscopy. It's an animation that rapidly switches back and forth between the slightly different views a person's right and left eye might see. Your brain then starts to merge the two together and you get the sense of depth. I'd be curious to hear if this trick works for you, given that your vision might not be accustomed to perceiving depth.
posted by the jam at 10:36 AM on July 16, 2012 [9 favorites]

Lots of prey animals, like chickens for example, have eyes on the sides of their heads, and must move their heads back and forth for depth perception. With only one eye, your depth perception perhaps relies more than ours on seeing distant things as smaller, but you also have to move your head to see how far away things are. Nearby things move a lot, distant things not so much. With two eyes, we get the distance picture without moving our head, because we see more of the left and right sides of nearby things (so they look quite different to each eye) but pretty much the same thing for distant objects. Our brain translates that difference into depth perception. But most of the time we're moving our heads anyway, so it's not much different from your view of the world, but easier in the sense that we don't have to move our heads for the effect to happen.
posted by weapons-grade pandemonium at 10:38 AM on July 16, 2012

I don't have any direct experience or visualizations for you, but in a sense you do have depth perception - monocular depth perception. There's quite a list of cues there - stereopsis and convergence cues (basically, muscle info about how far are your two eyes angling toward each other) are the major ones that require binocular vision. In daily life, I don't know that I can actually distinguish what in my vision is coming from binocular versus monocular information.

As for the difference between opening and closing one eye, I will say that it does look 'flatter' in a way that's hard to characterize, but the sensation of depth comes right back as soon as I move my head even very slightly from side to side. And from the list of depth cues, what I'm doing is giving myself motion parallax cues - very slightly different perspectives on the same scene that my brain can combine to get depth information. So I'd say that having stereopsis is a bit like having that motion parallax sensation all the time.

On preview - yep! I am also very curious to know if that wiggle illusion works for you :)
posted by heyforfour at 10:41 AM on July 16, 2012

Here is another example of wiggle stereoscopy which is kinda awesome.

Also, two eyes makes for a larger field of view.
posted by axismundi at 10:42 AM on July 16, 2012 [1 favorite]

Just walking around with one of my eyes closed, the first thing I noticed is that I'm much more aware of my nose. And that it blocks my seeing eye from seeing "around" it.

When looking out with both eyes, my nose almost vanishes. It's like it's there, but it's ghostly and not in focus. The only way I could make this happen with one eye shut was to look slightly up/tilt my head down. When I do that with both eyes, I don't see my nose at all.
posted by royalsong at 10:42 AM on July 16, 2012

My father lost an eye, but he could still appreciate some of the 3D hardcopy images I created by moving left and right, as in wiggle stereoscopy. Which, by the way, works just as well up and down as left and right.

After losing his eye, he said that the only real practical limitation was judging the last step when getting off a train or bus.
posted by StickyCarpet at 10:43 AM on July 16, 2012

Oliver Sack's wrote about a women who regained her ability to see in stereo which you might find interesting. If i'm remembering right he also wrote more about her in his latest book The Mind's Eye.
posted by SpaceWarp13 at 10:44 AM on July 16, 2012

Honestly, I don't think it's all that different.

I have gone through many days with essentially vision in only one eye. I am nearly legally blind without corrective vision. Growing up I would sometimes only have one contact left and no glasses, so I would wear one contact at a time for a few days. I have also tried covering one eye, and it's essentially the same.

I barely notice the difference in depth perception. The main difference is that the breadth of your vision is a bit wider with two eyes, but there's a lot of overlap between the two ranges so it's not that much wider.

IMO, you're probably not missing out on as much as you imagine.
posted by timsneezed at 10:44 AM on July 16, 2012 [2 favorites]

Wow. The Wiggle stereoscopy looks so strange. I guess the first thing I've noticed is that with this kind of stereoscopic vision, things somehow don't look as flat. I can tell more clearly that there is something beyond the images as they are presented to me.
posted by RapcityinBlue at 10:48 AM on July 16, 2012 [5 favorites]

Hold a finger up to a distant object. Focus on the finger, then on the distant object. The focus of the different parts of your vision shifts, but in each case the finger is still in front of the object.

With two eyes, this is different. When you focus on the finger it looks just the same as with one eye: the finger is clear, withe the object partly obscured behind. But when you focus on the object the behind, not only does it become clear, but the finger in front begins to "dissolve": the finger splits into two impressions, both faint, and with some gap between them. You can now see the whole of the distance object through the impressions of the fingers, as the two eyes fill in the blank spots of each. It is basically possible to "see behind" an object in your view.

That's the most obvious way that object at difference depths can be perceived, and though we don't always notice it, people with two eyes are always (to some extent) looking "through" nearby objects at something more distance. You see that outline of your nose at the side of your sight? Well two eyed people have two such outlines, but kinda ghostly and seethrough.
posted by Jehan at 10:48 AM on July 16, 2012 [7 favorites]

It's probably worth mentioning one of the weirder things about stereoscopy - ubiquitous double vision of things outside the plane the eyes are pointed at.

For example, if you're trying to shoot a handgun with both eyes open, when your eyes focus on the front sight of the gun, two copies of the target appear in the out-of-focus area. Similarly, if I look over the corner of my monitor to focus on the wall behind it, two copies of the monitor's logo appear. When only one of the copies obscures something, the intermediate space is a weird flickery there/not-there superposition of what each eye is seeing.

Which of these two copies usually "wins" is determined by your dominant eye. I'm right-handed but left-eyed, which makes some things (like shooting a rifle) very awkward.
posted by 0xFCAF at 10:49 AM on July 16, 2012

Simply from a personal anecdote perspective, I think it may not be as different as you might imagine. I've always had two eyes, but one has much better vision than the other. I spent several periods from childhood to high school with the bad eye covered completely, due to a patch and then several surgeries. I never noticed any difference in vision or depth or anything during those periods, and I don't when I cover it now. I wear (not very strong) glasses for distance, and in theory I could have a stronger lens for the bad eye, but my Dr's never saw any reason to bother. The other eye really does compensate, possibly to a degree that people with two good eyes wouldn't think it could.

The one thing is that obviously you're missing some peripheral vision on the side with no eye. I completely fail some aspects of driving vision tests that require me to see things out of the side of my weaker eye. But I just make sure to look in my mirror a bit more carefully. I'm pretty sure I could drive and see as well if that eye was missing completely.

(Oh hey, what timsneezed said!)
posted by DestinationUnknown at 10:50 AM on July 16, 2012

As someone who has both eyes but mostly lost the ability the merge the images into 3d, the biggest difference if you only have one eye is not the loss of stereoscopic vision but the reduced field of view. On a day to day basis the lack of 3d vision makes very little difference. 3D movies don't work and tight parking spaces are difficult. That's about it.

The reduced field of view is a much bigger difference.
posted by Justinian at 10:50 AM on July 16, 2012

I lost vision in one eye at 30 and I'm curious about your vision. Can you estimate the distance of several objects which slightly overlap? What about objects that do not overlap? I can still judge distance but I think that's a function of my brain compensating.

I haven't noticed any difficulty reading / following lines smoothly since my vision loss. Maybe that's particular to your vision?

Your question is intriguing. I don't think I can explain stereoscopic vision the same way I can describe having mono vision. Having two eyes makes the landscape seem richer, I guess. Seriously interesting question. On preview I can say that I think the other posters are incorrect when they say you aren't missing anything. Do YOU know you're missing it? Probably not. But as someone who lost vision later in life, I certainly miss the nuances. (Or turning left against traffic without saying an extra little prayer.)
posted by PorcineWithMe at 10:56 AM on July 16, 2012

You might be interested in reading more about ocular dominance columns.

Part of what happens when a child is young is the setting of certain pathways in the brain; because you lost sight in one eye at an age when these paths were already developed or mostly developed, your brain may still be able to interpret visual input in the way that a two-eye-having person does.

IANAneurobiologist, but my mom worked for this guy when I was in high school, and he and his partner won the Nobel prize for their work on ocular dominance columns in the 1960s and 1970s. By depriving kittens from using one eye, they showed that columns in the primary visual cortex receiving inputs from the other eye took over the areas that would normally receive input from the deprived eye. These kittens also did not develop areas receiving input from both eyes, a feature needed for binocular vision. Hubel and Wiesel's experiments showed that the ocular dominance develops irreversibly early in childhood development. These studies opened the door for the understanding and treatment of childhood cataracts and strabismus. They were also important in the study of cortical plasticity.[4] (emphasis mine)
posted by rtha at 10:58 AM on July 16, 2012 [3 favorites]

I lost a lot of vision in one of my eyes when I was young. I have terrible distance perception now. I can't play games like tennis and I knock drinks over when reaching for them at times. Driving isn't a problem though. I don't remember too much about what it was like with two good eyes, but I do remember a huge difference in 3D. With two good eyes I remember 3D being, well 3D. I remember reaching out to touch Michael Jackson at Disneyland and instead touching the lady in front of me's hair because it looked so up close. Now when I watch 3D, the glasses just make the distorted picture look clear like a regular movie. Those at home 3D glasses don't work for me either. Also I've never been able to see the hidden image in those magic eye posters since losing vision in one eye. So those are the only differences I can recall. Otherwise I generally don't notice it.
posted by side effect at 11:04 AM on July 16, 2012

Stereoscopic vision is roughly analogous to stereo hearing. That is, when you're listening with both ears instead of just one, you have a sense of the location and distance of the sound source based on the slightly different information reaching each ear.

Assuming you are not hearing-impaired, you could try listening to different types of sound environments "stereo" and with one ear plugged, which should remind you a sense of the greater complexity of information that comes from hearing with two ears.

If you can extrapolate that sense to vision, then maybe that will help you imagine what depth perception entails.
posted by La Cieca at 11:12 AM on July 16, 2012 [1 favorite]

I wish I could give you a better answer to your question. It's a fascinating one, as are all instances of "what is it like to have a sense that I don't have?".

When I cover one eye and walk around, everything looks the same, and I kind of feel like I have a general sense of how far away things are, but I make WAY more mistakes. Basically, I get "fooled" a lot, which tells me that my brain is making highly educated guesses about how far away objects are based on experience and monocular depth perception. Those guesses are pretty darn good, but not as good as the guesses my brain makes using stereoscopic vision.

I find that it's possible for me, when using only one eye, to mentally trick myself in to imaging that I'm looking at a flat photograph rather than the real world. This mental leap is considerably harder to take when I'm using both eyes - the depth of the world in front of me is really, really hard to ignore.

This is very similar to hearing with two ears versus just one (on preview, La Cieca and I had the same thought). With two ears, it's very hard not to automatically pinpoint the locations of sounds. You just KNOW that a sound came from the right or left, unless you're in an echo chamber or something. With one ear, you still have some degree of localization ability, but you can get confused much more easily. Plus, it's easier to imagine that sounds are coming from someplace other than they are.

For me, the feeling of covering one eye is very similar to the feeling of covering one ear. Functionally speaking there's not much lost, but I feel that locating objects and sounds in space becomes a task that requires some background cognitive effort, as opposed to a totally automatic function. I suspect you don't have a feeling of effort. In terms of the neuroscience, it's interesting to ask exactly how that happened (if it did). I'd love to find out!
posted by Cygnet at 11:21 AM on July 16, 2012

Interestingly (maybe?) my experience is very different from Cygnet's. When I cover one ear (or have one ear of my headphones stop working) it's very disorienting and annoying, but covering my bad eye makes no real difference. I don't make any mistakes and can't see anything as flat; a photograph and a 3D object look obviously different, and I can't trick my eye to see them any other way. I assume that's because I've always had very good hearing in both ears, but learned to compensate for having very little sight in one eye from birth.

I meant to say above, to be clear, I have experienced what it's like with corrective lenses for my weaker eye, and though they technically improve how I do on eye tests using only that eye, it doesn't actually improve my overall vision.
posted by DestinationUnknown at 11:31 AM on July 16, 2012

Something else that might be of interest (approaching your question from a different side) is Maurius von Senden's wonderful book Space and Sight (1960). It documents the experiences of congenitally blind patients (born with cataracts) whose are sighted by cataract surgery later in life. Their descriptions of their experiences are really fascinating, as their brains try to make sense of visual input in terms of size, space, depth and distance. Reading it forever changed my own sense of how I see, and made me very conscious of the particular cognitive tricks of parallax and stereo vision. It includes many very vivid descriptions of people trying to distinguish distant and near objects, and all the subtle visual cues of distance, that captures the peculiar sensations of depth perception. (It's also very beautifully written.) Many older libraries have copies, and I hope someone will do a reissue soon.
posted by finnb at 11:32 AM on July 16, 2012 [2 favorites]

Can you see holograms? I seem to remember that folks with vision in only one eye could see the hologram on the cover of National Geographic as if it were 3 dimensional. That was in 1984.
posted by vitabellosi at 11:35 AM on July 16, 2012

Fixing my Gaze is a book by the woman that Oliver Sacks wrote about who came to stereoscopic vision through training.
posted by matildaben at 11:36 AM on July 16, 2012

Another book you might find fascinating is Fixing My Gaze, about a neuroscientist who went from having stereoblindness to regaining her stereoscopic vision through intensive training, and who writes about her experiences here.
posted by datarose at 11:36 AM on July 16, 2012

I have a cousin who is a surgeon who is very, very near sighted. He opted to have laser correction surgery. On only one eye leaving the other still near sighted. His fear was that he would become far sighted and not be able to operate. He says it is like having one eye for far away viewing and one for near and that the brain adapts quickly. This is a highly educated, highly skilled medical professional who chose to do this.

Not sure what that means to you other than to know that he thought the risk of screwing up his good eye (for surgery) was far greater than what he would lose by not doing both and seeing in streroscopy.
posted by JohnnyGunn at 11:53 AM on July 16, 2012

Still, I'm curious as to what it's like to have stereoscopic vision? Can anyone give me a good description of it?

My father lost an eye due to disease, so the best way I can describe 3D vision is contrasting his experiences with mine when we saw the same thing.

Obviously, he couldn't see 3D movies, and when we saw one at Disneyland, he was wondering why people were reaching for the screen.

"The ball. It's just floating there."
"Well, I can see that it's close to the camera..."
"No, I mean, it's here in the room. It's right next to that guy's head in the row in front of us. I can touch it without getting up and walking to the screen. It's not on the screen. It's here with us now."

So, that's one way to explain it. Depth perception gives "closeness" an element where your sense of proprioception kicks in. It's not only "close." It's here.

Another contrast was when we tried to play racquetball. I could always beat him, because he couldn't easily hit the ball on the move. For every shot, he was always trying to stop in place so he could orient himself in space before swinging at the ball. With two eyes, that unconscious calculation just happens faster. Like getting a computer that's just processes things faster -- you don't know how slow your current computer really is until you start working with a faster one, because you've gotten used to the slowness.
posted by Cool Papa Bell at 12:07 PM on July 16, 2012

I am definitely the least qualified person to answer your question--I am almost entirely blind in one eye and have been since before I could remember.

Besides the usual issues with 3D movies, optical illusions, and hitting a baseball, there's one thing recently I noticed I have trouble with. If I am indoors, staring at a corner where two walls meet, without any other visual cues I cannot tell if the corner is coming towards me or away from me. Towards me meaning two walls that meet at a point that comes out into the space of a room and away from me meaning two walls that meet at a point that is recessed (like any corner of a room where two walls meet). From the texture and the shadows, I can tell that the two walls are meeting at a point but without any visual cues, I don't know if it is coming towards me or away from me. I assume someone with depth perception would not have this problem?

This thread is super interesting to me, because it's something I've always wondered myself.
posted by inertia at 12:47 PM on July 16, 2012

I have both eyes, but I also have strabismus. That means that, like you, I only see through one eye; unlike you, however, I can switch. It took until I was 12 before I realized that other people don't see like that.

I highly recommend reading Oliver Sacks' autobiographical portion of The Mind's Eye. He develops strabismus and loses his stereoscopic vision, which he has particularly treasured due to his hobbies. Here's a blurb, including some description from a woman who never had sterescopic vision but trained herself to have it.

I notice I have problems that other people don't in the following areas: jumping off of things (walls, steps, curbs) is very difficult as I can't quite prepare; driving at night is difficult because headlights don't give me the visual clues that I have in the daytime; sports that involve catching or hitting things (especially small ones) in the air (baseball, lacrosse, tennis, etc); I can't see Magic Eye pictures (am told I'm not missing anything).
posted by quadrilaterals at 1:22 PM on July 16, 2012

I only see in 2-d because I have really terrible amblyopia (Lazy Eye). I was diagnosed when I was about 2 years old. I spent my childhood being that kid with the eye patch.

Driving is an adventure for others in the car with me. I judge distance based on the size of objects. I have the scratched up bumpers to prove it.

I found the Wiggle Steroscopy to be freaky. It made me anxious.

Like quadrilaterals, I have real problems driving at night, sports involving me to follow a ball coming at me, and Magic Eye pictures. Also, screw 3-d movies. Screw them right to hell!


I have found that ice hockey was a sport I excelled in, I guess it's pretty easy to see a flat, black puck on marked ice.

I too have always wondered about this. So the thread with other cyclops views is comforting.

Flat forever!
posted by Ruthless Bunny at 1:29 PM on July 16, 2012 [1 favorite]

I think being amblyopic since birth and having 2-D vision has made it easy for me to do well in composing photographs than "normal" people, since I don't have to extrapolate the scene in my mind to what it will look like in 2-D.

Difficult things:
* Parallel parking
* Judging distance to stop lights when night driving
* Threading needles
* Lighting candles
* Catching balls and other thrown objects
* Walking through doors with ladders
posted by matildaben at 1:37 PM on July 23, 2012