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
77%
3%
14%
3%
27
flagFinland
75%
12%
6%
6%
16
flagSpain
72%
5%
11%
11%
18
flagthe Netherlands
67%
23%
2%
6%
46
flagCroatia
64%
11%
5%
17%
17
flagSwitzerland
60%
13%
13%
13%
15
flagGermany
58%
19%
12%
9%
134
flagCanada
53%
17%
17%
7%
28
flagItaly
52%
19%
25%
2%
36
flagNorway
52%
9%
14%
23%
21
flagthe United States
51%
18%
17%
11%
393
flagthe United Kingdom
48%
18%
19%
12%
270
flagIndia
47%
25%
17%
7%
121
flagthe Philippines
47%
15%
15%
21%
19
flagPoland
45%
21%
19%
13%
10738
flagRussia
44%
22%
22%
5%
18
flagRepublic of Ireland
40%
16%
24%
18%
37
flagFrance
40%
37%
15%
6%
32
flagAustralia
38%
19%
30%
11%
26
flagUnknown
34%
18%
29%
17%
769

Gender

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

Details

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