Science Question From a Toddler: What do blind people see?


This question—which comes to us from an Anonymous reader, asking for his or her formerly toddler own self—may sound like a zen koan, but I assure you, it has an answer. And probably not the one you're expecting. It's really a prime example of why I love doing the Science Question from a Toddler series—I get these questions that, on the surface, sound very "Duh", but end up leading to complex places.

So, what do the blind see?

It depends on the blind person. But the stereotypical assumption—that blind people live in the sort of black nothingness the sighted see when we close our eyes—is actually the most rare of all the possibilities.

What the blind really see varies quite a bit, depending on the cause of blindness and its severity, said Dean Bok, Ph.D., Professor of Ophthalmology and Neurobiology at UCLA's Jules Stein Eye Institute, and a researcher who's worked with the organizations Research to Prevent Blindness and the Foundation Fighting Blindness. Many people who are described as blind can perceive light. Even those who must use a cane or guide dog to get around are more likely to see the world around them as an indistinct fuzzy blur, rather than a formless void.

And that blur is likely to be in black and white.

You probably remember from grade school that there are two structures in our eyes—cones and rods—that enable us to see and perceive light. Rods are related to night vision. Cones to color vision and what we see during the day. But there's a bit more to it than that.

"Cones are extremely important, not only for color, but also for acuity," Bok said. "The ability to read fine print is from cones, not rods."

Basically, the worse your vision is, the less color you can usually perceive.

But what's really astounding is how new, high-tech treatments are changing what some blind people see. Cory Haas is a 9-year-old boy who lives in New York state. A couple of years ago, Bok told me, this boy was one of the people whose sight was limited to fuzzy, mostly colorless blobs. He couldn't read. He needed help walking. Today, Cory Haas can ride a bike and read books with large print. His sight is nowhere near perfect, but he's gone from being legally blind, to being just another kid who has to wear glasses.

The secret is gene therapy. Haas was born with a kind of degenerative blindness called Leber's congenital amaurosis. There are at least12 different kinds of LCA, but Haas' is caused by a defect in a single gene—rpe65.

"That gene produces an enzyme that bends Vitamin A into the form that we need for vision. Then it's ready to be attached to a group of proteins called opsins, and used by color and black and white photo receptors. That's what triggers the visual response," Bok said. "If you don't have the enzyme, you'll never see. Kids who have a totally non-functional rpe65 gene can't see at all. Some with a crippled gene have a semblance of vision but are really legally blind."

Because this type of blindness is based on a single, small gene in the retina, it's relatively easy for scientists to fix. They take an adeno-associated virus—a virus which is usually present in humans but not known to cause disease—remove most of its genes and patch a shiny, new, properly functioning version of the rpe65 gene into it.

Once injected into the eye, the virus goes to work doing what viruses do, i.e. invading cells and using their machinery to replicate its genetic information. But, in this case, that information is the rpe65 gene. Within a few weeks or months, the person has a supply of working rpe65 genes, churning out the enzyme they need to see.

Image courtesy Flickr user moriza, via CC


  1. I just can’t help but be amazed every time I read something like this. Truly fascinating. It won’t be long until a simple gene therapy session will fix my horrible near-sightedness.

    1. That wouldn’t work that way. Nearsightednss is not due to a defective gene in the retina, but rather a deformity of the eyball. Nearsighted people have elongated, not perfectly round eyeballs (such as a football). When the eyes are shaped this way, this doesn’t allow light to hit properly on the retina. The light falls short of the retina, or in front of it, causing you to be nearsighted. The concave shape of your eyeglasses bends the light so that it can hit the correct place on your retina, allowing you to see clearly. Farsightedness works in the same way, except the eye will be shaped more like an egg, so it’s the opposite. This mean the light that enters your eye is too long, and goes behind the retina or some infinite place. The concave shape of your eyeglasses bends the light back into the correct place on your retina as well.

  2. One of the best discussions of what it’s like to be blind can be found in a kids’ book by Sally Alexander. Alexander lost her vision at age 26. She shows us what she sees (as well as how she gets around, how she uses money, how she reads, and more) in DO YOU REMEMBER THE COLOR BLUE? (Viking, 2000)

  3. There was a groovy study done, around the turn of the century, about what totally blind people, who had always been blind, expected to see when their eyes were repaired and how reality matched up to it. It was done just after some kind of laser surgery, which could repair one kind of congenital eye malfunction, became routine. There was a clinic in Manhattan which was cranking out newly sighted persons on an assembly-line basis and the survey results were:
    1 – sight is very distracting at first
    2 – shadows are weird and cool
    3 – the amount of information on people’s emotion states that you’re supposed to be able to get by looking at them has been over-hyped

    1. Nadreck,
      I find your statement interesting (“3 – the amount of information on people’s emotion states that you’re supposed to be able to get by looking at them has been over-hyped…”).
      I’m a librarian and one of the challenges we face with technology is the use of text chat and the difficulty of ascertaining the emotions of the users when there is no visual feedback. Many studies have been done regarding a librarian’s proper usage of such information technology, with the intent that we provide a clear and cogent answer to our patrons without having all the normal cues of a person standing in front of us.
      I wonder if you have that study, or know where to get it—I’d like to read it.

      1. relating to marstein, he’s right, vision is dealt with in the brain by special areas that are wired to deal with it. i’ve read about brain scans done on people who have been blind since birth. the regions of the brain usually reserved for vision are used up by, oh, i guess other senses. the blind person who said that visual feedback is overrated for figuring out the mood probably just has a very finely developed sense with other senses, involving sound, but possibly involving smells, maybe pheremones that we’re not consciously observing, touch, being able to feel subtle movements another is making. it’s like sometimes you know when someone is watching you. it makes sense from an evolutionary perspective, someone who is aware that he is being stalked is more likely to survive. variations in the atmosphere (not literally), however tiny, can be picked up on. one of the things i find most fascinating is that the best is around when it needs to be. meaning, when humans were at constant risk of being picked off by predators, our senses were at a level that probably no one has today.

  4. I remember being mystified by this myself when I was young. I was thinking of what it would be like being absolutely blind. A teacher explained to me it would be like what we see from the back of our head. Nothing, with no sense of anything even being absent.

  5. My daughter has Leber’s and I hold hope that she will too get to see! In the short 2 years that I have been involved in the blind world, I have seen great leaps in advancements!!

  6. I’ve always wondered what blind people ‘see’ in their head when they hear sighted people talking about color. Or deaf people when they read about sound.

    Assuming these people had been born unable to see or hear.. how do they interpret information for which they have no frame of reference? Do they assign some alternate meaning to the words, or are they able to pick up on the concepts in an abstract sense?

    I’ve only known one blind person my whole life, and I never got the courage to ask him because I didn’t know if it’d be rude (I was pretty young). He didn’t have total blindness anyways, he had the light/dark blob thing going on.

  7. I have wondered about this myself and I don’t think the toddler got his question answered.

    There certainly are people in the world who are completely blind and have been so since birth. This is a toddlers idea of blind.

    When someone says “helicopter” to me, I “see” a picture of a helicopter in my head. It is in fact, impossible for me not to see one. What would someone who has never had a moment of sight in their life “see” when someone mentions a helicopter? I imagine they may think of the sound a helicopter makes but that does not work so well for a zucchini or a screwdriver or a coffee table.

    A completely blind person must have a totally different filing system in their brain to classify objects around them.

    1. The image of an Helicopter is only part of what comes to your mind when you think of it. Actually, what is the image of an helicopter? Do you imagine it a small one, a huge transport, a cartoon one?

      But there are also non-visual sensation associated with it: the noise of the engine, the wind from the blades, maybe the rolling or the nausea if you have ever been on one (I haven’t). What a ever-been-blind person associates with the idea of helicopter is different from what you do, but also what I associate is different from you, and I’m not blind!

  8. I think its important to realise we all think differently, blind or not.
    BdgBill mentions seeing a picture of a helicopter in his head when one is mentioned…I have mostly normal vision but cannot picture anything in my head at all…

    1. @#9:

      You’re right, even the sighted vary in what we can or do picture in our heads.

      I, for one, form vivid but imprecise mental images. However, when I read, very clearly *hear* every word, which many of my friends tell me they do not do. I started wondering about this when I found out many of my SF and fantasy-reading friends couldn’t pronounce many of the character and place names. I could never have made it through many of my well-loved R.A. Salvatore books if I hadn’t figured out what “Daermon N’a’shezbaernon” sounded like.

      1. I’m like your friends. When I see names like that I have a default sound or image or texture in my mind that represents the name.

  9. I’m also curious about the 3rd comment in the report Nadreck mentions – I dislike phone conversations because I find it difficult to assess the emotion of the other person without seeing their face. I wonder if their vision was not sufficiently fixed to be able to assess emotion? Or perhaps they have just become completely adept at judging emotion from vocal cues. (It is interesting how easy it is to tell if someone is smiling when talking, without seeing them).

  10. there was a small experiment that I did in some undergrad class that disproved the idea that you “see” a helicopter in your mind when you think about it.

    Picture a zebra in your mind…now count the stripes.

    No one could answer – so I think the conclusion is that you are not actually picturing a physical zebra in your mind.

    1. Anon #17: I’m not sure that your experiment proves anything. First, you could ask about other details that people would be able to answer, e.g. roughly how long is the zebra’s head compared to the length of its body? Second, I’m pretty sure any good artist (or other person with well-developed visual memory) who studied a zebra closely would not find it hard to answer your experiment’s question. The result of the experiment simply means that, as a result of their lack of familiarity with zebras/undeveloped visual memories, the subjects couldn’t form a clear, detailed visual representation of a zebra – not that they weren’t forming one at all.

    2. This doesn’t prove much.

      Perhaps it simply means the brain has only so much RAM for images, and so it displays most of the zebra vaguely, at low resolution, and only generates as much as it needs to.

      More importantly, the brain can only handle a certain number of objects at once. I can imagine 1 or 3 blueberries, but ask me to imagine 7 and I can’t- unless I mentally group them into 4 and 3. Zebras have far more stripes than we can focus on at once- they all seem to defy counting, even when I have a photograph in front of me. This is, after all, part of the point of a zebra’s stripes- so that predators have a hard time picking out where one zebra ends and another begins.

      1. There’s an anecdote by Braque, which google isn’t finding for me, to the effect that a child asked him how many legs a lobster had, and he had to draw one (from memory) to find out.

        A lot of accounts of what happens when we see are really about what happens when we see while thinking about what we’re doing. Merleau-Ponty for example spends several pages moving a pen to and fro, and watching it get bigger and smaller.

        What we actually do most of the time is just negotiate the real world without consciously seeing at all.

        It’s the same with mental pictures I think, the kind of mental picture you might use for a zebra or a helicopter would depend on why you happened to have formed it, and what you’re going to do with it.

    3. Say “picture a zebra in your mind” and I will come up with a blurry, black and white striped mass with the auditory word “zebra” in my mind (heavy on the z sound). Ask my autistic son to do the same and I bet he could count the stripes. Same file, different filing system.

    4. @anonymous 17
      Anyone who has tried to draw soomething or someone in front of him/her can tell you that observing something and recognizing something are somewhat different functions. When we recognize someone’s face, for example, we usually only see a few key elements –the nose, the eyebrows, the jawline, whatever; and then the brain sort of fills the rest of the gestalt in, with I-don’t-know-what. How often does a fellow shave off a beard, and the people who see him every day don’t notice, or they say, “Is something different?”

  11. I’ve never had much trouble ascertaining someone else’s emotional state via text/IM, especially if it’s real time, so I’ll give the blind people their credit there. (It is, however, a learned skill. I find adults who didn’t grow up with it have a really tough time with that.)

    That gene therapy is mind-blowing, btw. Not enough comments remarking on that.

    1. I’ve had this discussion with a lot of people. I find it fairly easy to discern hidden meaning and emotion from text/texting. Everything is based on experience and how a person interprets it. Blind people learn to read emotions various ways other than by sight, so when they become sighted, it’s strange and new to them. They have a hard time reading facial expressions or are unimpressed by it because it’s not in their experience to that point (and this assumes we’re talking about someone old enough to have these skills in the first place). Someone who was blind for a long time and then is given sight reacts the same way as someone who rarely or never texts. To them it’s outside their experience thus far and so unimpressive or difficult.

  12. Here’s a fun experiment that gives a sighted person a little more understanding about blindness:

    1) Place two spots on a piece of paper, about four inches apart, like this:
             @                              @
    A sharpie works best, if you only have a regular pen, fill them in and make them as dark as possible.

    2) close your left eye, and with your right eye look directly at the spot on your left.

    3) Slowly move the paper about 12-15 inches away from your face. For some people, the spot you’re not looking at disappears a little closer or farther away. It will disappear when it gets to your blind spot.

    1. randomcat,

      that experiment demonstrates the spot in your vision blinded by the entry point of your optic nerve, which is slightly off center at the back of your eye. It does not really demonstrate blindness.


      1. Hi Jenn. Yes, I was aware that’s where the optic nerve comes in. There’s a reason it’s called the blind spot. I note use of the word ‘blind’ in two apparently contradictory places in your post.

  13. This blog post kind of avoids answering the question.

    My assumption is that totally blind people can “see” an internal representation of their surroundings. They just don’t have color information or texture and shape details from things they haven’t touched.

    What I mean is that information coming from the retina is just a small part of the perceptual process. Other senses, memory and expectation are so entangled that most of the time we can’t be sure what sense provides which part of the perceptual combination. Or did we just expect to perceive something and included that perception from memory.

    For instance, fully working human visual system gives you accurate information from just an extremely tiny area (fovea) and most of everything you think you see just now is actually blur approximation enhanced by imagination and memory.

  14. I have a scar on the retina of my right eye that’s made me “legally blind” in that eye and what I see is basically the equivalent of a big sun spot. Stare into a light, look away and that’s what I see when I close my left eye.

  15. The “blind people can’t see helicopters” thing goes to show just how much people misunderstand or underestimate about blindness.

    A totally blind person can easily get a good idea about a helicopter. Just put them in the same room with one. Or hand them a toy one. They can’t tell you what color it is, but I bet they can tell you how it smells, which is a detail lost on most people.

    Watch this video about a blind guy who touches things and then paints them:

  16. I agree with self-propelled. I’ve never counted the stripes on a zebra before, even when confronted with one, so why should I now? But if i imagine a flower, or a 4-leafed clover, i can tell you exactly how many petals/leaves it has.
    The real question is…where is this image being “projected” a.k.a. where is the video screen in your brain?

  17. Wow, that’s utterly amazing! Maggie, thanks for this post. I always appreciate your science posts and it’s one of the main reasons I love Boing Boing so much–because I learn stuff!

  18. Interesting post. I had a visual defect from birth that basically prevented my left retina from developing properly. My right eye is completely normal, although a little near-sighted, but in my left eye I only have a little bit of peripheral vision surrounding what I’ve always called a “dead spot” in the middle.

    My brain basically turns my left eye off because of that (for lack of a better metaphor), leaving me looking only out of the right, but if I cover my right eye and force myself to see out of my left, I don’t see things and my peripheral vision and then a big black spot in the middle–I don’t see anything in the middle. No blur, no color, no shadow, no light. It’s like a complete absence of vision. It’s probably not completely analogous because I’m not completely blind, but it’s not something I’ve ever really tried to articulate before.

    But imagine the freakiness when I discovered that my brain would make up stuff for the dead spot. During a vision test given at my high school (not by my usual opthamologist), I was presented with three columns of black letters on a white background, to only my left eye. The middle row was in my dead spot, and my brain just extrapolated the white background to make up for what it couldn’t see. The examiner and I had a delightful “who’s on first”-type conversation when she asked me to read the middle column, and I patiently explained that “middle” didn’t mean anything if there were just two columns. Hilarity ensued.

  19. Like AnthonyC, I also hear everything I read in my “mind’s ear”. This must be as a result of the Phonics method I used when learning to read more than 60 years ago! This was in a country school and I think country school gave me an edge.

    1. If you hear every word in your head as you read, you’re doing it wrong. You have the ability to read far faster than anyone can speak, so if you have to speak every word in your head, you’re greatly limiting the speed at which you can read. You should try reading this way.
      And if you do happen to reach a word like “Daermon N’a’shezbaernon”, or just a word that you’re not familiar with, that’s when you can slow down, speak the word in your head, or aloud (but not on the subway, take it from me) and try to figure out how to say it correctly.

      1. It’s not true that one is reading wrong if they can “hear the words in their head” when they read. I can read very fast, and I hear the words in my head. I’m assuming I just don’t hear them at the rate of normal speech. I even hear the voice of the person who’s writing. There’s even a generic voice for things like news and magazine articles.

  20. To me, the “helicoptor zuchinni” question seems simple. I hear the word “helicoptor” and am assualted by a variety of parameters about helicoptors. The sound, the sight, the image of the word itself, the sound of the word, the rotor wash, etc… Same with a zuchinni…the smell, feel, look,taste, etc..
    Remove one sense and the others remain to give a complete (or as complete as our frame of referance provides) picture for our brain.

    I’m quite sure there are blind people who have much better vision than I will ever have.

  21. This reminds me of something that my children asked me, and it rang a bell for me too. Do blue eyed people see a blue eyed world and brown eyed people see a brown eyed world???????

    1. I would guess so to a degree. Blue eyed people are more prone to light sensitivity than their brown eyed counterparts. My entire blue eyed family is notoriously light sensitive and are known for our dark, cave like abodes, and inability to drive without hats and sunglasses.

  22. Jorge Luis Borges wrote about the experience of gradually losing his sight. If I remember correctly, his blindness at first manifested as a greenish or bluish mist.

  23. “the amount of information on people’s emotion states that you’re supposed to be able to get by looking at them has been over-hyped”

    I would imagine that learning to interpret emotions expressed on faces would be an important developmental milestone for typical children. I’m not surprised that a newly-sighted adult would not be able to discern emotions based on facial expressions well. Perhaps after years of classical conditioning this would improve. That in itself would be an interesting study to perform.

  24. awesome, i still thought gene therapy was in the theoretical stage. wonder how long until those designer babies we have been hearing about come along…

  25. “My research says that there are a lot of people who don’t ever naturally form images, and then there are other people who form very florid, high-fidelity, Technicolor, moving images,” he said. Some people have inner lives dominated by speech, body sensations or emotions, he said, and yet others by “unsymbolized thinking” that can take the form of wordless questions like, “Should I have the ham sandwich or the roast beef?”

  26. “the amount of information on people’s emotion states that you’re supposed to be able to get by looking at them has been over-hyped”

    No it hasn’t. What’s happened is that the blind person has never learned to see it. Ask all the autistic people out there about body language – especially high functioning autistics, who are in the extremely frustrating position of knowing they’re missing information, yet still missing it.

    I’m not Autistic, but I’m on the autistic end of neurotypical; I’ve had to study to fill in the “resolution” on my ability to read body language, but I basically fit in the normal human range. A person who has been blind their entire lives has ZERO practice doing it, and a lifetime of practice reading tone of voice – likely they’ve already re-purposed the part of the brain that reads facial expressions for something else more useful to a blind existence (tracking tone of voice, recognizing things by touch, spatially orienting by sound, etc) and getting that neural processing back is going to be nigh impossible by the time they’re an adult.

  27. I’ve had detached retinas in both my eyes, since fixed.

    During the first operation, my surgeon performed what he called a retrobulbar injection to anesthetize the eyeball and its muscles. This was to install a “scleral buckle”, a piece of rubber that dents the retina so the tissue can reattach.

    I saw nothing. Not black. No visual sensation from that eye whatsoever. After the anesthetic wore off, I saw mostly gray from the eyepatch–and many spots. This is quite common with the retinal laser treatment I had.)

    Most people can imagine having, or have even had, no aural sensation, but very few imagine no visual sensation, something that not even all blind people experience.

  28. Interestingly, the platypus has extremely limited visual acuity but its bill – which is hyper sensitive to electrical fields – can easily detect worms crawling through thick mud. Scientists have determined that this electrical sensing equipment ends up wired to the part of the brain that processes visual information… in other words, platypusses literally see with their honker (that is, “visual” images appear to them). I imagine that given a lifetime of blindness, a similar phenomenon might occur for those people trained in listening to echoes and through touch.

  29. I may not have read all the comments above, but no one seems to mention that seeing is a skill that the brain has to learn during the early years. If your brain doesn’t get wired for seeing until a certain age you will never completely learn it even if the hardware is restored at a later point.

    There was an article about a married man whose vision was restored and he almost regretted it.

  30. I’m an artist.
    When you say zebra, I’m definitely seeing a vivid zebra swishing its tail in my mind, savannah and muddy banks of a water hole under its hooves. I wouldn’t want to count the stripes, but I could give a good estimation of a number if you really wanted one.
    When I read The Autobiography Of Malcolm X, I strangely “heard” every word in Malcolm X’s actual voice~I had listened to a few of his lectures shortly before I read it.
    I “hear” the words of every book I read, I don’t know how to explain how that works.
    Reading the comments has really opened my eyes that individuals, sighted or not; have very distinctive thinking styles.

  31. I wanted to add that I do read very swiftly despite hearing every word, My grade school teachers would accuse me of not being “really” finished because I was done before anybody~at least until giving me a quickie comprehension quiz. It’s like hearing a narrator, I suppose.
    Pages of dialogue between two or three people slows down my reading speed a bit, but not by much.
    I assure you that I’m “doing it right”. Apparently everybody is different. Who knew, lol?

  32. Show the kid his own blind spot(s). You aren’t
    are of something you are blind to —not a big
    black hole, but nothing at all.

    Show him flowers under UV, his senses are not the
    only ones possible.

  33. I highly recommend John Hull’s account of going from normally sighted to deep blindness as an adult. A wonderful read. Also, I just finished The Brain That Changes Itself: When you lose sight, the areas of the cortex that handle vision get re-assigned to other senses, such as touch and smell. I think I’m right in saying people who are deeply blind don’t see black or dark, they just perceive with other senses.

    Agreed with Anon17’s conclusion about the number of stripes on an imagined zebra. The same issue exists if you imagine an air-conditioning vent and try to count the slats. Or a football boot and try to count the sprigs. The brain conceptualises objects rather than remembers specific images.

    A person who has never seen will still conceptualise but their concept will be based on touch, sound, smell/taste and what they’ve intellectualised from what they’ve been told about it.

  34. That didn’t really answer the question. What if the person doesn’t have any eyeballs. Does that person still see a black and white haze? Do they just see black or another color altogether? Black is a color, which means that a person with no eyeballs is seeing “something”. If they don’t perceive “anything”, doesn’t that make true blindness as incomprehensible for a sighted person as sight is for a blind person receiving zero visual stimulus?

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