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Comment by d4mi3n | Hacker News Reader

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.

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

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.

I... only see it happening with either both eyes or my right eye...

My left eye is immune? This is uncanny...

Sounds like your perception can't exactly be pigeonholed.

Boom, baby.

your taxi to the nearest wormhole awaits..

I’m the opposite! My right eye alone can’t see it, but can do with both or left only!

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.

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.

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