“Pigeon Neck” Illusion (2014)

[newaccount74]

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.

[albert_e]

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.

[jrumbut]

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.

[dawatchusay]

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?

[jameshart]

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!

[thomassmith65]

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.

[justinpombrio]

I'm confused what you think an illusion is?

[anamexis]

How would you define what an optical/visual illusion is?

[kuhewa]

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

[TylerE]

Pretty much. Change the color to yellow and it’s very obvious.

[tomelders]

I feel like this is doing what an animator would do, just badly.

[d4mi3n]

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.

[soxocx]

Thats interesting. I see it with either or both eyes.

[Daub]

As a one-eyes person, the illusion works fine for me. However, it ceases to work in the periphery of my vision.

[aendruk]

Astigmatism? My eyes blur at different angles so various anisotropies show up only when one is closed.

[stouset]

I let out a verbal "what the fuck" when I tried this. Same exact thing as you, it's absolutely striking.

[stefncb]

For me it weakens with one eye closed, but I still see it.

[IshKebab]

Worked a bit better for me with one eye closed. Weird.

[illegalmemory]

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 .

[userbinator]

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.

[xwdv]

Jesus, this illusion is so powerful, you’d have to have a very poorly optimized brain to really see anything else.

[cornstalks]

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.

[eyelidlessness]

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.

[sneak]

I can consciously toggle the illusion on or off.

[mafuyu]

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.

[ancientworldnow]

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.

[stefncb]

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.

[aoeusnth1]

Both me and my wife had to consciously blur our vision to see the illusion.

[sorokod]

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?

[aliqot]

I get what I'm supoosed to see but i dont see it, its pixels gliding continuously.

[zestyping]

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.

[clhodapp]

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.

[tolmasky]

Hey, this is built with Cappuccino!

[bella_sm]

DaVinci would have loved this!