Why is this an illusion at all?

Factual Questions
61

I tried it a little later but I guess it was still early because they were all concave.

However.

I’ve just tried it again now and relived the initial experience. It was shorter though, just a matter of seconds, maybe fractions of a second really.

It starts with a collection of whitish objects and before I really notice what each thing is they appear to resemble a cluster of pearls to me, both in color and (I guess) in shape. I’m only fractions of a second into my perception when I begin to focus on the rectangular plate in the upper right hand corner (I don’t know why I always start with that point) and the big, round plate below it. These two objects definitely look convex, just as they did in my first experience with this illusion. I still remember my original experience when all the objects in the image seemed to be bulging out like white candy, especially the string of plates at the bottom. By the time I decide to reverse my perception, one second has already passed. The rectangular plate in the upper right hand corner and the round plate below it turn concave in a few fractions of a second, and the really amazing thing is the simultaneous sensation that the picture takes on depth and every object seems to sink in. It’s short and slightly overwhelming because I can almost feel it in my guts. Two seconds have passed and all the plates are concave again, with amazing clarity and minutiae.

Here’s the link again: https://twitter.com/slackerinc/status/1050255308906524672?s=21

62

And before I finish drinking my coffee I want to say I’m really intrigued by the original illusion as well: https://twitter.com/slackerinc/status/983475717492101120?s=21

It is funny how my senses persist in perceiving the four horizontal tapes as sloping upwards and downwards while my brain can easily “see” they’re horizontal and parallel.

63

Cool images, cool illusions! With the original image, if I rotate my iPad 90° (ETA: rotation about the axis of the image’s plane) and look at a shallow angle (almost coplanar, but not quite, with the image), the diamonds and other “noise” are eliminated and the 4 bold bluish-purple lines are clearly parallel. As I increase the viewing angle, the “noise” comes into play for my eye and the illusion takes hold.

And the plates and their crater effect is fascinating too. I can’t recreate the initial convex appearance. Every time I look, they are now concave. Maybe I need a longer break from the image.

64

Easier still is to stand to the side of your computer and look across your screen at a severe angle.

65

That’s what I said.