[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!

[the_af]

> 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.

[IshKebab]

Not really - he's saying when it's fully black there is no illusion. The chicken is really moving like that.

[mannykannot]

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.

[maegul]

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.