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
flagthe United Arab Emirates
76%
4%
16%
4%
25
flagFinland
75%
12%
6%
6%
16
flagSpain
72%
5%
11%
11%
18
flagCroatia
64%
11%
5%
17%
17
flagthe Netherlands
60%
28%
2%
8%
35
flagGermany
59%
18%
13%
8%
122
flagPakistan
57%
7%
21%
14%
14
flagCanada
53%
17%
17%
7%
28
flagNorway
52%
9%
14%
23%
21
flagthe United States
51%
18%
17%
11%
387
flagItaly
50%
21%
25%
3%
32
flagthe United Kingdom
47%
18%
20%
12%
261
flagthe Philippines
47%
15%
15%
21%
19
flagIndia
46%
26%
17%
7%
117
flagPoland
45%
21%
19%
13%
10265
flagRussia
43%
25%
18%
6%
16
flagFrance
41%
35%
16%
6%
31
flagAustralia
41%
20%
29%
8%
24
flagRepublic of Ireland
40%
16%
24%
18%
37
flagUnknown
34%
18%
29%
17%
731

Gender

men43%
women45%
red one
43%
45%
blue one
17%
22%
none of them
22%
18%
both of them
16%
13%

Details

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