“Pigeon Neck” Illusion (2014)(michaelbach.de) |
“Pigeon Neck” Illusion (2014)(michaelbach.de) |
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.
Brighter colors make it a bit less strong but still very much there.
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!
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.
As a pixelated image, I dunno: our insistence on viewing groups of pixels as shapes is an illusion to start with.
There really is an image there when viewed at the intended scale.
This just relies on poor contrast.
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.
My left eye is immune? This is uncanny...
If the illusion is an error, what maximizes it?
Nothing to see here, move along.
Edit: checked Firefox and Chrome on Android and they look exactly the same (work on me). Low brightness works better than full brightness.
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.
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.
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?
(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!”
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).
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.
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.
Curious to see if anybody with expertise on the topic of optics or visual perception chimes in with some insight.
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.
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.
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.