Our Retinas don't send raw data to our brain like a camera sensor would. Instead, the neurons in the retina already do some pre-processing, like boundary detection, or movement detection. The brain then receives signals where movement was detected.
This movement detection is basically just detecting changes in light level, so it works better when the contrast is high (dark gray vs. white) and works less good when contrast is low (dark grey vs black).
So our brain gets stronger "movement" signals when there is high contrast, and it looks like the part that has high contrast is moving faster. Since the image is designed in a way that the boundary of head/body always have low/high contrast or vice versa, it seems they are moving with different speeds.
The illusion was very strong on my mobile screen and non-existent on my desktop screen. The screen calibration was different in the latter I believe so the pigeons were appearing as a slightly different colored grey blocks visually distinct from the vertical bars.
On my laptop, I am only able to see the illusion if I looked at the striped background and blur my vision a little. Then it is quite impressive and strong. Otherwise, it always appears perfectly smooth for all colors.
I don’t feel this is much of an illusion. I think you just can’t see the movement of gray on black. Or maybe this is what illusions are in a very simple form?
Play with the color of the pigeons. Slide it all the way to black, and it's no longer an illusion - the edges really do move in steps. Slide it all the way to white and the same effect appears in the inverse.
Somewhere in between, there are shades of gray where the smooth movement of the pigeons is visible. And there are shades of gray where your brain can't separate it from the underlying black motion. That's interesting, no?
That's what makes all optical illusions interesting - exploring the thresholds where our brain's perceptual machinery takes shortcuts.
I've noticed there's a tendency, especially among smart people, to be dismissive of optical illusions. 'I didn't fall for it' - because to a certain personality, it's important to feel like your mind can understand things and you can't be 'fooled'.
But good optical illusions aren't fooling you. You don't need to feel defensive about whether you were 'tricked'. They're hacks that exploit edge cases in your visual cortex, and cause your brain to be fed erroneous data. They're interesting and useful because they help you calibrate the instruments your brain uses to collect data!
On the other hand, with black-on-black, the idea that there is something representing a moving pigeon is a sort of illusion in itself, as you infer a boundary that you never see in full.
On the third hand, movement is an illusion in all cases: what's really happening is that static pixels are changing color and brightness (the pixels may jitter slightly in changing color, but that's not the motion we perceive.)
All these views seem to me to be reasonable, they are just different perspectives.
For me, just with the color slider, there was nearly always some sort of illusory motion. Transparent perception of the actual motion of the pigeons was either impossible or required precise conditions, which really affirms the power of this effect.
Let's say you recreate this effect by painting the pigeons onto a transparency sheet, and moving the sheet above a paper with a striped background. The pigeon shapes would appear to bend, when in fact they do not... so in physical form, it clearly is an illusion.
As a pixelated image, I dunno: our insistence on viewing groups of pixels as shapes is an illusion to start with.
The image is a grid of pixels. When a group of the pixels that the human viewer perceives as a worm appears to grow, we cannot claim that the pixels in the overlap actually belong to the background. It is equally valid to claim they belong to the worm, in which case... the worm actually has lengthened.
In the physical version, if the worm/pigeon and the grid are exactly the same color, we still consider them separate entities.
In the digital version, if a group of pixels appears to be part of some object, that's as good a reason as any to argue it is part of that object (though strictly speaking, it's a meaningless question since it's just a bunch of pixels).
One is an illusion, or the set of all illusions, and the other is the set of all images generated by pixels.
Not all images generated by pixels are an illusion. Otherwise you would say that all images generated by, say, acrylic paint, are an illusion because they're made of molecules.
That we perceive paintings of objects as objects is an illusion, clearly. But that is not the same illusion as this "pigeon neck" thing.
An illusion is not an illusion if what you perceive is what is actually happening.
The whole point of the "pigeon neck" illusion is that it tricks the eye into perceiving areas as growing that we know are incapable of growing. If the areas are inelastic matter, that's a cool effect: we know that a printed image on a transparency sheet cannot truly grow just by sliding it around a table.
If the areas are pixels... it's less significant. Nothing is actually moving to start with. It's all neighboring lights flashing on and off. If a group of those lights is part of an object, it's only to the extent that the viewer perceives it as such.
Note that this is not the case with other digital illusions. This one in particular is ruined because it relies on a strip of pixels 'belonging' to one of the two (perceived) objects that sandwiches it.
Images on a screen, or a painted painting, etc, I disagree.
There is, objectively, data being presented, which we perceive.
You're glossing over the importance of a particular scale, the scale at which humans operate in on a daily basis, and making the assumption that reality is what's happening at a smaller scale.
This is incomplete.
If we want to talk about the image, the underlying components become progressively less important as the scale decreases. When we view a painting, or an image on a screen, when are less interested in up quarks, down quarks, and electrons, and more interested in the image and the medium.
There is room for disagreement in some cases. “Look how the black text becomes invisible when it goes in front of a black background” is not what I would call an optical illusion, for instance.
I would describe an illusion as something where my (say) visual cortex is lying to me. This results in an image looking very odd: I _know_ that one thing is happening, but it looks like something else is happening.
Black text going in front of a black background doesn't have that effect. My knowledge of what I'm seeing agrees with what I see. My knowledge is "there is black text in front of that black text", and my visual cortex says "sure, I can't see it but that's perfectly plausible". This pigeon video does have that effect. My knowledge says that the pigeon image is moving smoothly, but I can clearly see its head bobbing; there's a disagreement.
Do other people define "illusion" differently? Or perceive something differently?
The color stepping feet version[1] I think definitely qualifies. The color contrast is high enough that if you focus on the leading or trailing edge of the "feet" it's trivial to see its moving the whole time, but if you look at the entire thing as a whole, the "stepping" effect appears.
When your brain fudges the results of what you're seeing because of some hidden processing heuristic. If the bird were actually just colored black, then what we would see would be accurate. But its presented as if we should percieve continuous movement when we really shouldn't.
I’m just saying upon initial thought that it seemed too simple to be considered an “illusion” because it doesn’t rely on some mental trickery, just blindness. But I’m willing to accept that optical illusions may all rely on some form of blindness. Glad to spawn the conversation!
With the pigeons it seemed illusory, but with just worms you can tell that's exactly whats happening. Dunno if it is the single-row shape or just less action on the screen allowing you to focus on one cell
I was in bed reading this with an eye closed and was very confused until I discovered the illusion works for me only when I watch it with both eyes open.
I found this surprising—I know three dimensional optical illusions depend on focus and perspective, but I was unaware two dimensional optical illusions were as well.
You are right. If I tilt the screen while changing distance to the screen and keep blinking with my eyes while I do this, I, besides looking like a maniac, can weaken the effect and even make it disappear entirely.
I also see it with any number (>= 1) of eyes open and at any angle. Wonder if GP's phone was on night shift or something similar - the article mentions that color changes impact the illusion's visibility.
Interesting, I have astigmatism so I tried it without my glasses and with both one and two eyes open at different angles and I still see the illusion (with no change in intensity of the “bobbing”)
For me, if I focus intensely on the head, the neck stops moving. When I relax, and the reference naturally changes to the lines in the background, the neck begins moving again.
It would have been interesting to control the width of the vertical stripes too , to see at what point it "starts" being a illusion. I assume for very thin stripes it might not work so well .
This seems to be, for lack of a better analogy, an effect of rounding colour intensities in the "motion compensation" processing of the brain. The grey and black become perceived as identical and thus no motion is detected in those areas where the two colours are overlapping.
It took me several minutes before I could see the illusion. I just saw grey rectangles and pigeons smoothly moving to the right and had no idea what the “illusion” was supposed to be.
Now I wonder how much it depends on the gamma. I understand there's some differences depending on the hardware, browser and image format/metadata. By default we may all see a different shade of grey, affecting how much of an illusion we get.
Edit: checked Firefox and Chrome on Android and they look exactly the same (work on me). Low brightness works better than full brightness.
That’s certainly a possible factor. I’m on an iPhone 14 Pro with brightness at medium levels in an averagely lit room using Safari. I just tried on my Mac’s XDR display and it’s similar: I can either see or not see the illusion (now that I know what the illusion looks like I can turn it on/off in my head).
> It took me several minutes before I could see the illusion. I just saw grey rectangles and pigeons smoothly moving to the right and had no idea what the “illusion” was supposed to be.
Same here. After a bit I could see some worm stretching if I focused on particular points in the image.
I noticed that as soon as I registered all of the movement, my eyes fixed a certain way that they do when I'm driving and navigating an overly complex traffic situation. I was super reluctant to try to focus them any other way.
When I started messing with the color I ran into that. If I shifted to a different grey, it just looked smooth to me. But either extreme, black or white, and the illusion was there.
I see it, but it doesn’t feel optimal. What my brain is telling me I see is different from what I know is true about what’s on the screen. It seems to be interpolating between nearly and actually overlapping with each alternating stripe.
There are a lot of ways it’s optimal to be able to approximate and fill in details like this with normal visual processing, but literally not being able to unsee falsehoods (and I can’t switch it off in my brain like another commenter said they could) doesn’t feel like one of those optimal scenarios to me.
A highly optimized brain doesn’t bother wasting time on getting fine details like this correct, it’s too slow and will lead you to getting killed in situations where a rough approximation of what you are seeing is good enough. People have to focus very hard to turn off the optimizations and see what is really going on, some can’t do it at all. Some people seem to be able to see the smooth linear motion by default, perhaps descendants of those who lived in simpler environments.
Why do you think it takes more time and brain power to see the rectangles and pigeons correctly (smooth movement)? It was instantaneous and natural for me. I’m not convinced by your logic. It doesn’t seem like a disadvantage for a brain to naturally register the image correctly rather than being fooled by an illusion, especially when it takes zero effort.
(I think people like to call this “steel man” or whatever but just generally applying a charitable interpretation…) I think their take on optimization is about falsehoods about reality that our brains assimilate to make functioning or survival possible under certain circumstances, like perceiving magenta as not-green or being able to observe a field of grass without being hyper aware of each blade of grass within it.
All of which is good insofar as it actually serves us, but it’s really weird to me to frame it so absolutely. It’s not an optimization if it doesn’t serve us and we’re just misperceiving reality for no purpose, and there’s nothing wrong with you or anyone else who doesn’t. If anything it’s just… “wow, electrified meat evolved to be conscious is really wacky and super subjective!”
Yeah, this effect is pretty strong. After staring at it a bit, the only way I found to 'break' it was by noticing that if I flicked my eyes towards a bird, there was a brief period before the illusion kicked in. By constantly flicking my eyes between each bird, I was able to perceive them as moving linearly.
They're just sliding smoothly for me unless I look at it without any focus as a disinterested viewer. I work on fixing moving pixels all day though so maybe I'm not an average subject.
Here's my attempt at explaining this phenomenon:
Our Retinas don't send raw data to our brain like a camera sensor would. Instead, the neurons in the retina already do some pre-processing, like boundary detection, or movement detection. The brain then receives signals where movement was detected.
This movement detection is basically just detecting changes in light level, so it works better when the contrast is high (dark gray vs. white) and works less good when contrast is low (dark grey vs black).
So our brain gets stronger "movement" signals when there is high contrast, and it looks like the part that has high contrast is moving faster. Since the image is designed in a way that the boundary of head/body always have low/high contrast or vice versa, it seems they are moving with different speeds.
The illusion was very strong on my mobile screen and non-existent on my desktop screen. The screen calibration was different in the latter I believe so the pigeons were appearing as a slightly different colored grey blocks visually distinct from the vertical bars.
Funny, I still get the illusion after turning the pigeons every color from dark grey to bright yellow.
Brighter colors make it a bit less strong but still very much there.
On my laptop, I am only able to see the illusion if I looked at the striped background and blur my vision a little. Then it is quite impressive and strong. Otherwise, it always appears perfectly smooth for all colors.
I get the illusion for yellow, but not for bright red or blue. That's interesting....
I don’t feel this is much of an illusion. I think you just can’t see the movement of gray on black. Or maybe this is what illusions are in a very simple form?
Play with the color of the pigeons. Slide it all the way to black, and it's no longer an illusion - the edges really do move in steps. Slide it all the way to white and the same effect appears in the inverse.
Somewhere in between, there are shades of gray where the smooth movement of the pigeons is visible. And there are shades of gray where your brain can't separate it from the underlying black motion. That's interesting, no?
That's what makes all optical illusions interesting - exploring the thresholds where our brain's perceptual machinery takes shortcuts.
I've noticed there's a tendency, especially among smart people, to be dismissive of optical illusions. 'I didn't fall for it' - because to a certain personality, it's important to feel like your mind can understand things and you can't be 'fooled'.
But good optical illusions aren't fooling you. You don't need to feel defensive about whether you were 'tricked'. They're hacks that exploit edge cases in your visual cortex, and cause your brain to be fed erroneous data. They're interesting and useful because they help you calibrate the instruments your brain uses to collect data!
> Slide it all the way to black
For the record: the illusion still works for me if I slide the color all the way to black. One eye, both eyes, it always works for me.
Not really - he's saying when it's fully black there is no illusion. The chicken is really moving like that.
On the other hand, with black-on-black, the idea that there is something representing a moving pigeon is a sort of illusion in itself, as you infer a boundary that you never see in full.
On the third hand, movement is an illusion in all cases: what's really happening is that static pixels are changing color and brightness (the pixels may jitter slightly in changing color, but that's not the motion we perceive.)
All these views seem to me to be reasonable, they are just different perspectives.
For me, just with the color slider, there was nearly always some sort of illusory motion. Transparent perception of the actual motion of the pigeons was either impossible or required precise conditions, which really affirms the power of this effect.
Let's say you recreate this effect by painting the pigeons onto a transparency sheet, and moving the sheet above a paper with a striped background. The pigeon shapes would appear to bend, when in fact they do not... so in physical form, it clearly is an illusion.
As a pixelated image, I dunno: our insistence on viewing groups of pixels as shapes is an illusion to start with.
How is viewing an image on a screen an illusion?
There really is an image there when viewed at the intended scale.
The image is a grid of pixels. When a group of the pixels that the human viewer perceives as a worm appears to grow, we cannot claim that the pixels in the overlap actually belong to the background. It is equally valid to claim they belong to the worm, in which case... the worm actually has lengthened.
Yes, but the illusion occurs when the worm/pigeon and the grid aren't actually the same color.
In the physical version, if the worm/pigeon and the grid are exactly the same color, we still consider them separate entities.
In the digital version, if a group of pixels appears to be part of some object, that's as good a reason as any to argue it is part of that object (though strictly speaking, it's a meaningless question since it's just a bunch of pixels).
You're talking about two different things.
One is an illusion, or the set of all illusions, and the other is the set of all images generated by pixels.
Not all images generated by pixels are an illusion. Otherwise you would say that all images generated by, say, acrylic paint, are an illusion because they're made of molecules.
That we perceive paintings of objects as objects is an illusion, clearly. But that is not the same illusion as this "pigeon neck" thing.
An illusion is not an illusion if what you perceive is what is actually happening.
The whole point of the "pigeon neck" illusion is that it tricks the eye into perceiving areas as growing that we know are incapable of growing. If the areas are inelastic matter, that's a cool effect: we know that a printed image on a transparency sheet cannot truly grow just by sliding it around a table.
If the areas are pixels... it's less significant. Nothing is actually moving to start with. It's all neighboring lights flashing on and off. If a group of those lights is part of an object, it's only to the extent that the viewer perceives it as such.
Note that this is not the case with other digital illusions. This one in particular is ruined because it relies on a strip of pixels 'belonging' to one of the two (perceived) objects that sandwiches it.
Images on a screen, or a painted painting, etc, I disagree.
There is, objectively, data being presented, which we perceive.
You're glossing over the importance of a particular scale, the scale at which humans operate in on a daily basis, and making the assumption that reality is what's happening at a smaller scale.
This is incomplete.
If we want to talk about the image, the underlying components become progressively less important as the scale decreases. When we view a painting, or an image on a screen, when are less interested in up quarks, down quarks, and electrons, and more interested in the image and the medium.
I'm confused what you think an illusion is?
There is room for disagreement in some cases. “Look how the black text becomes invisible when it goes in front of a black background” is not what I would call an optical illusion, for instance.
I would describe an illusion as something where my (say) visual cortex is lying to me. This results in an image looking very odd: I _know_ that one thing is happening, but it looks like something else is happening.
Black text going in front of a black background doesn't have that effect. My knowledge of what I'm seeing agrees with what I see. My knowledge is "there is black text in front of that black text", and my visual cortex says "sure, I can't see it but that's perfectly plausible". This pigeon video does have that effect. My knowledge says that the pigeon image is moving smoothly, but I can clearly see its head bobbing; there's a disagreement.
Do other people define "illusion" differently? Or perceive something differently?
It's th e same illusion as someone walking out a door and somehow teleporting to another door after they walked around outside.
The color stepping feet version[1] I think definitely qualifies. The color contrast is high enough that if you focus on the leading or trailing edge of the "feet" it's trivial to see its moving the whole time, but if you look at the entire thing as a whole, the "stepping" effect appears.
1: https://michaelbach.de/ot/mot-feetLin/index.html
Something that relies on unexpected or weird characteristics of the human visual system.
This just relies on poor contrast.
How would you define what an optical/visual illusion is?
When your brain fudges the results of what you're seeing because of some hidden processing heuristic. If the bird were actually just colored black, then what we would see would be accurate. But its presented as if we should percieve continuous movement when we really shouldn't.
I’m just saying upon initial thought that it seemed too simple to be considered an “illusion” because it doesn’t rely on some mental trickery, just blindness. But I’m willing to accept that optical illusions may all rely on some form of blindness. Glad to spawn the conversation!
With the pigeons it seemed illusory, but with just worms you can tell that's exactly whats happening. Dunno if it is the single-row shape or just less action on the screen allowing you to focus on one cell
Pretty much. Change the color to yellow and it’s very obvious.
Yellow doesn't do it for me. But orange, oh boy.
I feel like this is doing what an animator would do, just badly.
I was in bed reading this with an eye closed and was very confused until I discovered the illusion works for me only when I watch it with both eyes open.
I found this surprising—I know three dimensional optical illusions depend on focus and perspective, but I was unaware two dimensional optical illusions were as well.
Thats interesting. I see it with either or both eyes.
I... only see it happening with either both eyes or my right eye...
My left eye is immune? This is uncanny...
I’m the opposite! My right eye alone can’t see it, but can do with both or left only!
Sounds like your perception can't exactly be pigeonholed.
Boom, baby.
your taxi to the nearest wormhole awaits..
The illusion is much less if I zoom in and even less if I close one eye, so maybe they had their device up close to their face?
You are right. If I tilt the screen while changing distance to the screen and keep blinking with my eyes while I do this, I, besides looking like a maniac, can weaken the effect and even make it disappear entirely.
Try closing one eye and tilting your head 90°
I can see it irrespective of how many eyes are open or any tilt angle.
So you can see it with zero eyes open? ;)
I also see it with any number (>= 1) of eyes open and at any angle. Wonder if GP's phone was on night shift or something similar - the article mentions that color changes impact the illusion's visibility.
No night shift, for what it’s worth. Another commenter mentioned astigmatism, which I do have. I was not wearing my glasses at the time.
Curious to see if anybody with expertise on the topic of optics or visual perception chimes in with some insight.
Interesting, I have astigmatism so I tried it without my glasses and with both one and two eyes open at different angles and I still see the illusion (with no change in intensity of the “bobbing”)
Can you see it with three eyes opened?
I can’t but I’ll ask my yoga guru tomorrow.
As a one-eyes person, the illusion works fine for me. However, it ceases to work in the periphery of my vision.
Astigmatism? My eyes blur at different angles so various anisotropies show up only when one is closed.
I do have an astigmatism in my right eye—which was also closed. First time I’ve had this happen with an optical illusion, though.
I let out a verbal "what the fuck" when I tried this. Same exact thing as you, it's absolutely striking.
I was confused as well. First impression: nothing. Get up and look with both eyes and there it was. Interesting stuff.
For me, if I focus intensely on the head, the neck stops moving. When I relax, and the reference naturally changes to the lines in the background, the neck begins moving again.
For me it weakens with one eye closed, but I still see it.
Worked a bit better for me with one eye closed. Weird.
It would have been interesting to control the width of the vertical stripes too , to see at what point it "starts" being a illusion. I assume for very thin stripes it might not work so well .
This seems to be, for lack of a better analogy, an effect of rounding colour intensities in the "motion compensation" processing of the brain. The grey and black become perceived as identical and thus no motion is detected in those areas where the two colours are overlapping.
Jesus, this illusion is so powerful, you’d have to have a very poorly optimized brain to really see anything else.
It took me several minutes before I could see the illusion. I just saw grey rectangles and pigeons smoothly moving to the right and had no idea what the “illusion” was supposed to be.
Now I wonder how much it depends on the gamma. I understand there's some differences depending on the hardware, browser and image format/metadata. By default we may all see a different shade of grey, affecting how much of an illusion we get.
Edit: checked Firefox and Chrome on Android and they look exactly the same (work on me). Low brightness works better than full brightness.
That’s certainly a possible factor. I’m on an iPhone 14 Pro with brightness at medium levels in an averagely lit room using Safari. I just tried on my Mac’s XDR display and it’s similar: I can either see or not see the illusion (now that I know what the illusion looks like I can turn it on/off in my head).
> It took me several minutes before I could see the illusion. I just saw grey rectangles and pigeons smoothly moving to the right and had no idea what the “illusion” was supposed to be.
Same here. After a bit I could see some worm stretching if I focused on particular points in the image.
I noticed that as soon as I registered all of the movement, my eyes fixed a certain way that they do when I'm driving and navigating an overly complex traffic situation. I was super reluctant to try to focus them any other way.
When I started messing with the color I ran into that. If I shifted to a different grey, it just looked smooth to me. But either extreme, black or white, and the illusion was there.
I see it, but it doesn’t feel optimal. What my brain is telling me I see is different from what I know is true about what’s on the screen. It seems to be interpolating between nearly and actually overlapping with each alternating stripe.
There are a lot of ways it’s optimal to be able to approximate and fill in details like this with normal visual processing, but literally not being able to unsee falsehoods (and I can’t switch it off in my brain like another commenter said they could) doesn’t feel like one of those optimal scenarios to me.
A highly optimized brain doesn’t bother wasting time on getting fine details like this correct, it’s too slow and will lead you to getting killed in situations where a rough approximation of what you are seeing is good enough. People have to focus very hard to turn off the optimizations and see what is really going on, some can’t do it at all. Some people seem to be able to see the smooth linear motion by default, perhaps descendants of those who lived in simpler environments.
Why do you think it takes more time and brain power to see the rectangles and pigeons correctly (smooth movement)? It was instantaneous and natural for me. I’m not convinced by your logic. It doesn’t seem like a disadvantage for a brain to naturally register the image correctly rather than being fooled by an illusion, especially when it takes zero effort.
I agree with you.
(I think people like to call this “steel man” or whatever but just generally applying a charitable interpretation…) I think their take on optimization is about falsehoods about reality that our brains assimilate to make functioning or survival possible under certain circumstances, like perceiving magenta as not-green or being able to observe a field of grass without being hyper aware of each blade of grass within it.
All of which is good insofar as it actually serves us, but it’s really weird to me to frame it so absolutely. It’s not an optimization if it doesn’t serve us and we’re just misperceiving reality for no purpose, and there’s nothing wrong with you or anyone else who doesn’t. If anything it’s just… “wow, electrified meat evolved to be conscious is really wacky and super subjective!”
I can consciously toggle the illusion on or off.
Yeah, this effect is pretty strong. After staring at it a bit, the only way I found to 'break' it was by noticing that if I flicked my eyes towards a bird, there was a brief period before the illusion kicked in. By constantly flicking my eyes between each bird, I was able to perceive them as moving linearly.
They're just sliding smoothly for me unless I look at it without any focus as a disinterested viewer. I work on fixing moving pixels all day though so maybe I'm not an average subject.
If I look directly at a point, the illusion goes away there. And I don't really see anything strong anyway, so I wonder how you see it.
Both me and my wife had to consciously blur our vision to see the illusion.
[dead]
I wonder what is the maximal extent of the craining and the shrinking illusion that can be achieved. Is it to do with the velocity? The grid thiknes?
If the illusion is an error, what maximizes it?
I get what I'm supoosed to see but i dont see it, its pixels gliding continuously.
This isn't an illusion at all. Things that are too dark to see... are too dark to see.
Nothing to see here, move along.
Something I noticed and got a kick from: If you set the color to black or white then the real motion and the illusion are indistinguishable.
Hey, this is built with Cappuccino!
DaVinci would have loved this!