How is this polygon called? (the one over the circles)

square
rhomboid
concave square
concave rhomboid
In this Ehrenstein illusion the sides of a square placed inside a pattern of concentric circles take an apparent curved shape. But in reality, the sides are straight.
Debbie Fox
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Correct this question
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Very interesting!
reach: rather globalgeometryillusionsmathematicsoptical illusionstechnology

Answers by country

square
rhomboid
concave square
concave rhomboid
answers
flagPoland
69%
12%
9%
7%
30422
flagFrance
68%
20%
4%
8%
25
flagAustria
64%
8%
12%
10%
56
flagSwitzerland
64%
5%
23%
5%
39
flagGreece
64%
14%
7%
14%
28
flagGermany
62%
11%
18%
7%
379
flagthe United Kingdom
62%
8%
16%
10%
260
flagCanada
62%
12%
12%
11%
72
flagthe Netherlands
62%
6%
20%
3%
29
flagSingapore
61%
23%
15%
0%
26
flagthe United States
60%
12%
17%
7%
1010
flagUnknown
60%
9%
9%
19%
41
flagIndonesia
57%
5%
26%
10%
19
flagAustralia
55%
15%
13%
16%
80
flagRepublic of Ireland
48%
14%
14%
18%
27
flagMalaysia
47%
13%
21%
17%
23
flagPakistan
47%
9%
33%
4%
21
flagIndia
46%
15%
19%
15%
413
flagthe Philippines
41%
13%
16%
24%
65
flagthe United Arab Emirates
37%
25%
14%
17%
35