They discuss people from the educated, democratized world see rectangles while a group from Namibia see circles because, they hypothesize, their world isn't highly "carpenterized" with right angles and straight lines. So could this not be simply because they don't know what a rectangle is, and so categorize these close loops as circles? I don't understand the acceptance it is an optical illusion.

  ________
 /        \
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Do you see the above as a circle or a rectangle?

If you don't see the circles, this shows what to look for:

https://i0.wp.com/mentalbomb.com/wp-content/uploads/2023/03/...

At first I saw rectangles then I searched for the circles and found them. Now I'm having a hard time going back to seeing rectangles.