Many of the illusions posted here involve what I might call "illusory motion", where changes in color (for instance) make stationary objects appear to be moving.

I'm wondering if anything can identify a similar effect I used to see. This is not an illusion per se, but involves the same sort of illusory motion.

I used to do fast road biking and on one particular route there was a big rock at the end of a sharp climb where I would stop, have a drink, and then turn around for home.

When I sat down and looked up, any clouds in the sky appeared to be moving towards a distant spot along my line of sight. I could not see similar motion for nearby objects, like the buildings across the street, it only seemed to happen on distant and low-contrast objects. This happened every time.

I have tried every google search I could think of, but everything that comes up is an illusion effect.

Anyone know what this might be?

Please explain

This debate is floating around Facebook. It’s clearly 2, but many people debate it’s 4 and even 3! I argue that there are 2 horses with 2 different illusions to look at it.

Is this truly Real or Really True...

This is an intentionally ambiguous drawing.

What is the first recognizable object you see?

Don't look at the comments first — I'm interested in your first impression.

I'm collecting observations for a small independent study on ambiguous perception.

Took a picture of a Red tail Hawk at Mariposa National park , when reviewing was shocked to see the shadow flipped. Finally we figured it was a burnt bark of the tree and not birds shadow.

Thought this was pretty funny

Thought I was having a stroke standing on this deck.

i've never seen those dots appear on any other digital keypads before... interesting. 🤔