Which of the lines on the right, is the continuation of the black line on the left?

red one
blue one
none of them
both of them
This is known as Poggen­dorff il­lu­sion, first de­scribed in 1860. Many detailed studies of the illusion point to its prin­ci­pal cause: acute angles in the figure are seen by viewers as ex­pand­ed.

Answers distribution

red one
blue one
none of them
both of them
answers
flagFinland
75%
12%
6%
6%
16
flagSpain
73%
6%
6%
13%
15
flagthe United Arab Emirates
71%
4%
19%
4%
21
flagCroatia
69%
15%
7%
7%
13
flagPakistan
61%
7%
15%
15%
13
flagGermany
60%
18%
13%
8%
111
flagthe Netherlands
57%
30%
3%
9%
33
flagCanada
53%
17%
17%
7%
28
flagthe United States
51%
18%
18%
11%
374
flagItaly
48%
22%
25%
3%
31
flagFrance
48%
33%
14%
3%
27
flagthe Philippines
47%
15%
15%
21%
19
flagNorway
47%
11%
17%
23%
17
flagPoland
46%
22%
18%
12%
8182
flagthe United Kingdom
46%
19%
21%
11%
242
flagIndia
46%
26%
18%
6%
115
flagAustralia
45%
22%
22%
9%
22
flagRepublic of Ireland
42%
15%
21%
21%
33
flagRussia
40%
26%
20%
6%
15
flagUnknown
37%
17%
30%
14%
287

Gender

men46%
women46%
red one
46%
46%
blue one
17%
23%
none of them
20%
17%
both of them
14%
12%

Details

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