Human Fovea Detector
Mood
excited
Sentiment
positive
Category
tech
Key topics
computer graphics
shader programming
human vision
A Shadertoy project simulating or detecting the human fovea, showcasing an interesting application of graphics programming.
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- 01Story posted
11/13/2025, 12:48:45 AM
6d ago
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11/13/2025, 1:18:16 AM
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Step 02 - 03Peak activity
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Step 03 - 04Latest activity
11/17/2025, 9:20:27 PM
1d ago
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I would check to make sure this can't trigger migraines or seizures. Maybe it's just me, but also, please double check.
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.
> I would check to make sure this can't trigger migraines or seizures. Maybe it's just me, but also, please double check.
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.
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.
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.
Edit: seems like there isn't enough research to suggest the latter. Apologies
X X X
X and X X
X X XThe 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.
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...
:(
"Bad request"
am I missing the joke?
https://web.archive.org/web/20210430091013/https://www.shade...
Too bad that we associate monetizing a demoscene site with getting paid for your work.
By definition you have to be paid to call it work.
Is the exception to the rule.
Any other question?
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?
Maybe it doesn't work on small/AMOLED screens?
> 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.
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.
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?
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".
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.
oh I see fovea
UPDATE: And yep, there (mostly) is! https://www.shadertoy.com/embed/4dsXzM?gui=false&paused=fals...
On a retina Mac I had to double the scale value to get reasonable results.
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.
This is a flickering blue/green image. In the center wherever your eyes are looking, you will see a dark spot.
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.
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.
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
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!
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