It depends on whether your brain interprets the light source as on the right or on the left. Once you understand that, you switch at will. Just a variation on many such perceptual illusions. Is it a vase or two faces? Is it an old woman or a young girl? Etc.
The fun thing is you can do it over and over again. Once you see them right side out, if you turn away and look back, they are inside out again until you look at the one that’s not again.
Don't have to look away really. I keep staring looking at different plates and they flop back and forth.
Unconscious Inference of visual perception.
Thank you, I've seen this kind of thing before but never realized what was happening. I wish we could figure out how to use this to help elect Biden
[en.m.wikipedia.org]
@Lorajay this goes a long way in explaining the Trump syndrome.