[HN Gopher] Human Fovea Detector
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Human Fovea Detector
Author : AbuAssar
Score : 451 points
Date : 2025-11-13 00:48 UTC (22 hours ago)
(HTM) web link (www.shadertoy.com)
(TXT) w3m dump (www.shadertoy.com)
| herodotus wrote:
| Amazing - but iPhone screen is too small. Works on my iPad.
| zeckalpha wrote:
| Worked on my iPhone
| intrasight wrote:
| Just zoom in a bit
| dotancohen wrote:
| That's due to the retina display. Try fovea.
| altairprime wrote:
| What's the correct scale for 210dpi?
| jchw wrote:
| 180 worked pretty well on my Framework 16.
| zellyn wrote:
| Ditto on my MacBook Air
| avidiax wrote:
| You can also increase the "lengt". Doubling it works well on my
| Macbook, and the pattern is more dense so you can see your
| fovea better.
| zamadatix wrote:
| It depends on viewing distance as well.
| Arete314159 wrote:
| Hi, I don't know what this is supposed to do, but I get pretty
| bad migraines and loading the page made me feel extremely strange
| almost immediately so I closed it.
|
| I would check to make sure this can't trigger migraines or
| seizures. Maybe it's just me, but also, please double check.
| irilesscent wrote:
| Its supposed to show you how big of a radius your eye can focus
| on at a time, as we age the radius shrinks.
|
| Edit: seems like there isn't enough research to suggest the
| latter. Apologies
| sho_hn wrote:
| I don't know why you got downvoted. This seems like a very
| useful contribution.
| krisoft wrote:
| I also don't think it is downvote worthy.
|
| The first part of the comment is very valuable. "I looked at
| it and it made me feel extremely strange almost immediately".
| That is very good to know.
|
| The second bit I'm less sure about. What do they mean by
| "check to make sure this can't trigger migraines or
| seizures"? Like what check are they expecting? Literature
| research? Or experiments? The word "check" makes it sound as
| if they think this is some easy to do thung, like how you
| could "double check" the spelling of a word using a
| dictionary.
| skinner_ wrote:
| I interpreted it loosely, as "be aware of the possibility,
| and stop looking at it at the first signs of issues".
| nkrisc wrote:
| That seems to me to be a VERY generous interpretation of:
|
| > I would check to make sure this can't trigger migraines
| or seizures. Maybe it's just me, but also, please double
| check.
| Fabricio20 wrote:
| Interesting, I wonder.. have you ever tried a VR headset? Does
| that cause you migraines as well? or maybe any other discomfort
| that'd prevent you from using it?
| thenthenthen wrote:
| Not op but, VR is no problem, but this microsoft ar/mr
| glasses gave me an instant crazy headache in places I did not
| even know I had matter (back of the head), apparently thats
| the visual processing part of your brain. Terrible experience
| that lasted an hour or so.
| lloeki wrote:
| I don't usually have headache migraines but do have strong
| visual auras from time to time.
|
| Looking at this it first looked fun: "whoa, that's cool, this
| fovea thing is really smaller than I imagined"
|
| After a minute or so playing around I closed the window and
| then I noticed a form of retina persistence that looked eerily
| similar to an onset of a visual aura, as well as some faint but
| clear ear ringing, both typical symptoms of the migraines I
| experience.
|
| I immediately walked away from the computer and although
| dwindling it's still in effect 10min out.
| isoprophlex wrote:
| Yes. Occasional migraine sufferer with aura here. Don't look
| at this unless you want to spend the next 15 minutes worrying
| "am i getting an aura or not".
| nkrisc wrote:
| How would someone possibly "check" that? What method are you
| proposing?
| kalium-xyz wrote:
| there are a lot of papers on this (some made by inducing
| seizures in people under lab conditions). The most seizure
| causing things you could display are simply bars or a grid
| with moving details, sizes, or alternating in colors.
|
| Basically if it gives you a headache to stare at or just has
| this sucky attention grabbing feel to it when you look at it
| its likely to cause seizures. I CBA to dig up the papers on
| this but there are a bunch if you want to really get into
| this.
| ashtakeaway wrote:
| You should be arsed to dig it up because your parent
| comment is insinuating disbelief or sarcasm with quotation
| marks.
| kalium-xyz wrote:
| Here is the study that came to mind:
| https://www.cell.com/current-
| biology/fulltext/S0960-9822(17)...
|
| However as the above study iirc doesn't directly state
| that these patterns cause discomfort and doesn't contain
| any examples I suggest reading chapter 10 "Photosensitive
| Epilepsy and Visual Discomfort" of "hierarchies in
| neurology (1989)" on page 70-71 which proposes this AND
| contains an example you can look at yourself.
| kalaksi wrote:
| Yes, immediately felt weird and a bit uncomfortable. I can
| almost see, or kind of sense, all those parts moving in the
| image even though I can only see the movement clearly in the
| center. I can easily imagine getting a headache from watching
| that for a longer time.
| pixelpoet wrote:
| Hah, so my comment here spawned a post:
| https://news.ycombinator.com/item?id=45904434
| AbuAssar wrote:
| Yup :)
| willbicks wrote:
| This is a truly incredible demo.
| cachius wrote:
| Way cooler than the title suggest. I nearly didn't click.
| BriggyDwiggs42 wrote:
| Does anyone know how the hell this works
| shrinks99 wrote:
| You can see everything in your field of vision, but the area
| DIRECTLY in the centre has the highest level of detail. This
| image has high frequency animated details that are not
| cognisized equally by your entire FOV. The animated bit right
| in the middle at any given time is where your brain processes
| the most detail and also where you are looking.
| BriggyDwiggs42 wrote:
| Oh cool so it's about the frequency?
| robotresearcher wrote:
| Spatial frequency, ie. small detailed things, not temporal
| frequency (in this example).
| Peteragain wrote:
| I had to think about it, but are you saying all the stars are
| animated to rotate, but the amount they move between frames
| is too small for you to see unless it's in your fovea?
| pxndxx wrote:
| They are tiny and the ones not on your fovea don't register
| enough "pixels" for your brain to recognise the rotation.
| Sharlin wrote:
| They're just so small that you only see shapeless blur
| outside your fovea. If you applied an artificial blur
| filter to the whole screen, you'd also not see any movement
| anymore because all high-resolution detail is removed. A
| 3x3 box blur will erase differences between
| X X X X and X X X X X
| retrac wrote:
| Most of what you think you are seeing at any moment is only
| imagined.
|
| The retina is not uniform. Most photosensitive cells (cones)
| are near the centre of vision. Peripheral vision has little
| resolving power. Can't make out fine details. The reality of
| this is much more extreme than it subjectively feels like. The
| eye doesn't actually have pixels but if it did they'd all be
| focused at the centre. Like an image where 10% of the area in
| the middle had 80% of the pixels.
|
| At the centre of vision the eye has enough resolving power to
| make out the tiny star shapes and see that they are rotating.
| Outside of that narrow zone in the peripheral vision they're
| perceived as coloured blobs, at best. Normally your brain would
| make this transparent to you. But this is an unusual pattern.
| Your visual cortex doesn't realize all the stars should be
| rotating. So only the ones you can actually see at any one
| instant seem to rotate.
|
| Try to look at an object in the room with you, such as a lamp,
| without looking at it directly. Observe it out of the corner of
| your eye. The more you try, the less sharply defined it will
| seem. At the very edge of your vision you're only getting a
| handful of pixels worth of colour information. But because you
| know it is a lamp, it has the sharpness of a lamp's definition
| even though you cannot actually see that definition without
| directly looking at it. That's a related illusion.
|
| This is why the eye scans constantly in those micro-jerking
| motions known as saccades. If a face were to pop up on your
| display, it would feel like a single instant recognition of a
| person. But before you experience that the eye would scan over
| the eyes, mouth, nose and so on, several times, in sharp
| flicking motions, over about 100 milliseconds, and these dozen
| or so little snapshots, as it were, would be stitched together
| into the whole image of a face. Even though only a tiny slice
| of the eye, or the nose, etc. can actually be seen at any one
| time, you perceive the whole face.
|
| This illusion hacks that and reveals how narrow our high-
| resolution vision really is. The whole visual field feels
| rather high resolution. But only that tiny spot where they
| rotate actually is.
| dotancohen wrote:
| Is it a problem if the shape that I see rising stars in is
| not round? I get an upside down L shaped mass of rotating
| stars, no matter where I look in the image.
| AlecSchueler wrote:
| It's like an upside down egg for me.
| dalmo3 wrote:
| I get some slightly rotated pear shaped thingy but also
| varies with where I'm looking at. Crazy!
| shmeeed wrote:
| For me it's an L shaped blob as well. Not circular at all.
| ahoka wrote:
| It's also interesting to look at the second hand of a stopped
| watch to see the opposite effect.
| tzs wrote:
| > Most of what you think you are seeing at any moment is only
| imagined
|
| For some great illustrations of this I recommend people take
| a look at the Nova episode "Your Brain: Perception Deception"
| [1]. Nova episodes usually are only available to watch for
| free for a couple months after they air, then you have to be
| a PBS contributor, but occasionally old episodes become
| temporarily available. This one happens to be available now,
| with the video embedded at the link I gave.
|
| The whole thing is worth watching, but for the material most
| directly relevant to this you can start at the 7:13 minute
| mark, where it briefly discusses a well known optical
| illusion and why it works, and then looks at the question of
| if you brain can fake your perception so much to make that
| illusion work, just how much of what you see in normal scenes
| is real? Then they go into how you only have about 1 degree
| of high resolution vision at the center.
|
| A couple minutes after that there is a demo showing an
| interesting way to exploit that. They put the host in an eye
| tracker that can figure out where she is looking. Then they
| have her read some text on a monitor and she has no trouble
| reading. But when the camera shows us the monitor we see that
| almost the text is just the letter 'X' with small groups of
| letters briefly switching to other letters and then going
| back to 'X'.
|
| When we read our eyes don't smoothly scan the text. They
| actually look at a fixed point for a moment, then jump to
| another fixed point, and so on (the "saccades" mentioned in
| the above comment). This isn't just when reading. This is how
| we look at everything.
|
| She can read the text because the eye tracker is figuring out
| where she is looking a the software shows the real text
| there. As soon as her eyes jump that text goes back to 'X'.
|
| When we look at the text and aren't looking exactly where she
| is we might detect the change to normal text where she is
| looking but we can't read it because most of the time it will
| be outside of the small high resolution center of our vision.
| By the time we can move our eyes down to it her eyes have
| jumped and that text is back to 'X'.
|
| We don't consciously control the jumps so we can't sync ours
| to hers, so at best all we can hope for is to occasionally
| get lucky and maybe get a couple words now and then.
|
| [1] https://www.pbs.org/wgbh/nova/video/your-brain-
| perception-de...
| lossolo wrote:
| We're sorry, but this video is not available.
|
| :(
| keyle wrote:
| TL;DR it helps you identify the true diameter of your visual
| focus, which is said to shrink with old age (mine shrinks more in
| terms of _time_ dimension but that's a different issue!)
|
| For best results, use it _fullscreen_, change the #define `90`
| values to a higher value if you're on a high dpi screen.
|
| Stare at a few places on the screen and you'll get the effect of
| appearing to rotate only where you stare.
|
| It's pretty neat.
| leeoniya wrote:
| ok, i dont get it.
|
| on my phone at typical distance and 90 scale i only see about an
| asprin tablet size area spinning. but at 180 scale i see almost
| everything spinning at same distance.
|
| i think peripheral vision is quite sensitive to movement/contrast
| changes, but the moving shapes have to be large enough to trigger
| those receptors?
|
| not sure what to conclude from this.
| hekkle wrote:
| I don't get it, all I see is:
|
| "Bad request"
|
| am I missing the joke?
| gpm wrote:
| No, there should be a shader (think video) rendered showing a
| bunch of tiny spinning things. Something went wrong when you
| tried to load the page. It's an optical illusion where only
| things close to the centre of your vision look like they are
| spinning and everything else looks still.
| hekkle wrote:
| Okay, thanks.
| Taterr wrote:
| Shadertoy got hugged to death by this shader a few years ago and
| it had a custom "please go away" banner for a little while. Funny
| seeing it show up again on HN front page.
|
| https://web.archive.org/web/20210430091013/https://www.shade...
| joenot443 wrote:
| That's pretty cute. IQ's a good guy, he's had every opportunity
| over the years to monetize Shadertoy but it's stayed free and
| true to its purpose for 12y now.
| wilg wrote:
| it's too bad we associate paying people for their work with
| not being a good guy
| yeasku wrote:
| Keeping a site free for others to learn and share art is
| being a good guy.
|
| Too bad that we associate monetizing a demoscene site with
| getting paid for your work.
| imcritic wrote:
| The site is unavailable, because it is infected with cloudflare.
| MintPaw wrote:
| Seem iquilezles has finally given in. He's been complaining
| about crawler attacks a lot in the last months/years.
|
| https://x.com/iquilezles/status/1977172864785957340
| https://x.com/iquilezles/status/1976866381099679817
| https://x.com/iquilezles/status/1838858759336267842
| naIak wrote:
| How can you have problems hosting a website that is so
| obviously cacheable.
| junon wrote:
| .... Which is why he used cloudflare. Caching isn't magic.
| shadowgovt wrote:
| How strange; it worked on my machine. Is your network
| incompatible with Cloudflare?
| xfz wrote:
| I have nystagmus (rapid, uncontrollable, rhythmic eye movements),
| so I couldn't see anything at first, just lots of small dots.
|
| I had to zoom in (Mac accessibility tool) but then I could see
| the effect briefly. My eyes go everywhere, but I could see
| patches of moving shapes with stationary shapes further away,
| only that the patch moved around a lot!
| danielvinson wrote:
| I can't see any movement, at any distance. How likely is it
| something weird with my vision vs. something weird with my
| monitor/computer? I'm on a 360hz monitor at 2k.
| koolala wrote:
| The sizing and distance to you your face is important so you
| can play with that and change #define scale at the top.
| cornonthecobra wrote:
| At the default scale of 90, I can't see anything spinning at all
| even with the video full screen. If I set the scale to 250 or
| larger I can see the stars spinning, but I just see the whole
| field spinning. Even if I get so close to the screen it almost
| fills my field of vision.
|
| So for me either the stars are too small to see any motion, or I
| can see them all spinning no matter what.
|
| What effect am I supposed to see?
| yreg wrote:
| Try it in full screen, if you did not.
|
| > What effect am I supposed to see?
|
| I can see only a tiny area in the center of my vision animate
| (at default scale). The larger the scale, the bigger the area.
| tspng wrote:
| If I set the scale value (150) to roughly the ppi of my screen
| (4k 27"), I can see the effect. You should see the rotating
| stars only in a small field of view (fov) where your eyes are
| focused and all other stars should seem to remain still.
| cornonthecobra wrote:
| My phone screen is a bit over 500 ppi. I tried it full screen
| across the entire range that it's in focus (I'm mildly
| nearsighted), and I could just see the things spinning across
| the whole field if the pinwheels were big enough to see
| motion at all.
|
| Maybe it doesn't work on small/AMOLED screens?
| antirez wrote:
| Awesome. You'll see the little stars rotating only in the area
| they reach your fovea, the most sensible part of the retina. All
| the rest will not be able to perceive any motion.
| svdr wrote:
| I first thought the spinning was an optical illusion, like
| https://www.nationalgeographic.com/science/article/how-our-b....
| But in this case the spinning is real and you don't see the
| rotation except in a small area (your fovea).
| maxlin wrote:
| This is quite cool, rocked back and forth from and to my screen
| and got a (bit inconsistent, but consistently visible) "shape" of
| the fovea. maybe 30% larger than I thought it'd be!
|
| Right after though, I felt like my vision was clouded, like there
| was a grey overlay on it or something for a few minutes. Don't
| recommend having this open for too long. Visual cortex doesn't
| like running against its limits I guess
| stavros wrote:
| Oh wow, this made me realize something I've had for 20 years:
| When I look too close for a few seconds, I get blurriness at the
| center of my vision. It goes away after a while, but this made me
| realize that the blurry region is actually my fovea!
|
| I have no idea why my fovea blurs when I look close up at
| something, and doctors haven't been able to figure it out, but at
| least now I can google it better.
| dalmo3 wrote:
| That reminds me of myself as a kid looking at the moon and
| losing focus after just a few seconds. I could never figure it
| out.
| smusamashah wrote:
| The links seems to be down. From what I gathered, this is its
| video https://www.youtube.com/watch?v=3RUcQV3rd9k
| pacoverdi wrote:
| Reminds me of this app that is supposed to clear up your brain
| when staring at the screen for a while
|
| https://www.paulkeeble.co.uk/posts/cff/
| wartywhoa23 wrote:
| This actually does work!!
| gear54rus wrote:
| How do you know?
| wartywhoa23 wrote:
| Feels like a gentle rub on the skull from inside, and the
| overall feeling is akin to that of a lucid dream, but with
| a bit of nausea. Not too pronounced of course, but
| detectable.
| rosstex wrote:
| >clear up your brain
|
| Just to be clear, we don't actually know what that does right?
| Like, there's no link to this making up for poor sleep or
| improving your cognitive function right?
| smallnix wrote:
| Babies would go nuts over this, so much contrast and movement
| marginalia_nu wrote:
| Fascinating. I get very different results depending on which
| glasses I use.
|
| I'm far-sighted with a relatively weak prescription.
|
| Without glasses I have a tiny bit of lazy eye, it's not really
| perceptible for the most part looking at me, but for stuff like
| this I get a sort of figure-eight shaped blob of motion that
| skips around a fair bit which I guess is because my eyes fail to
| track correctly and can't find anything to focus on. Can't
| perceive the motion outside of this area.
|
| With my regular glasses this there's still some of this effect,
| but much less pronounced. Can't see any motion outside of the
| center of my field of view.
|
| With my reading/screen glasses, which technically makes me
| myopic, I get a large perfect circle, and can still detect a lot
| of motion outside of the circle, even if it's "low FPS".
| davidhs wrote:
| The strength of the glasses alters the size of the image that
| lands on your retinas. More (-) means a smaller image thus you
| stop seeing movement much closer to the focal point.
| qwertytyyuu wrote:
| woah its incredible how quickly i can spot the fuzzy spot around
| where i can clearly see the rotation, and when i unfocus can see
| fuzzy movement all around. This is really cool. So this is the
| theory beind foveated rendering/streaming
| NKosmatos wrote:
| What kind of sorcery is this? Incredible visualization!
| wartywhoa23 wrote:
| I wish there was an url parameter to share this fullscreen right
| away!
|
| UPDATE: And yep, there (mostly) is!
| https://www.shadertoy.com/embed/4dsXzM?gui=false&paused=fals...
| ludicrousdispla wrote:
| It's important to point out that all of the crosses are rotating,
| so this is effectively showing which parts of your vision are
| susceptible to change blindness (which is effectively 99% of it).
| zdc1 wrote:
| This would make for a cute screensaver
| sd9 wrote:
| The idea is to look at the scene and observe which crosses are
| rotating. You will notice that in your peripheral, the crosses
| appear not to rotate (although they are, and you can check that
| by focusing on them). This gives you an idea of how large your
| fovea is.
|
| On a retina Mac I had to double the scale value to get reasonable
| results.
| astroflection wrote:
| I get about 4cm wide at 50cm distance.
| smusamashah wrote:
| Discovered Maxwell's Spot illusion while looking further into
| this
| https://www.psy.ritsumei.ac.jp/akitaoka/Maxwell_spot_illusio...
|
| This is a flickering blue/green image. In the center wherever
| your eyes are looking, you will see a dark spot.
| ge96 wrote:
| does your brain just give up when the little stars seem to be
| still until you focus on one/a few
|
| oh I see fovea
| tgbugs wrote:
| A fully psychometric version of this that explores more than just
| the fovea could be created by varying the scale parameter (if you
| crank it up high enough you can see the movement in the
| periphery). The additional component you would need is to have
| trials where the subjects has to report whether a particular
| region (could even be cued with a red circle, I don't think it
| needs to be random) is actually moving or not while fixated on
| the center. There are clearly cells that detect this kind of
| motion in the periphery but they need larger visual input,
| possibly because the receptive fields of the cells that feed in
| are larger out there.
| ladon86 wrote:
| It's not possible to smoothly move your eyes unless you are
| tracking a moving object. Your eyes always move in saccades
| (quick jerky movements), unless there is a smoothly moving
| object, in which case your eyes gain the ability to track it
| smoothly.
|
| https://www.shadertoy.com/view/tXSBWt
|
| Here is a version with a smoothly moving red circle; notice how
| you can now move your eyes smoothly around the screen as you
| track the circle.
| scotty79 wrote:
| That's how small the high quality input to your neural network
| is.
|
| All your smart neurons start their inputs there (let's skip
| hearing for a moment). Every time you did math it worked on
| neurons with their roots at this small bunch in the visual
| cortex.
|
| It's a tool for reusing training data. When you move your eyes
| around same neurons are fed new data samples.
|
| It's basically same trick that convolutional neural nets use.
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(page generated 2025-11-13 23:00 UTC)