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
flagCroatia
75%
8%
8%
8%
12
flagSpain
73%
6%
6%
13%
15
flagFinland
73%
13%
6%
6%
15
flagthe United Arab Emirates
66%
5%
22%
5%
18
flagthe Netherlands
64%
24%
0%
12%
25
flagPakistan
61%
7%
15%
15%
13
flagGermany
60%
18%
13%
7%
109
flagCanada
52%
20%
16%
8%
25
flagthe United States
51%
18%
17%
11%
362
flagthe Philippines
50%
11%
16%
22%
18
flagItaly
48%
20%
27%
3%
29
flagFrance
48%
33%
14%
3%
27
flagPoland
47%
22%
17%
12%
7287
flagIndia
46%
26%
18%
6%
115
flagUnknown
46%
15%
28%
9%
32
flagNorway
46%
13%
20%
20%
15
flagAustralia
45%
22%
22%
9%
22
flagthe United Kingdom
44%
19%
22%
11%
212
flagRepublic of Ireland
39%
17%
21%
21%
28
flagRussia
35%
28%
21%
7%
14

Gender

men50%
women46%
red one
50%
46%
blue one
17%
23%
none of them
17%
17%
both of them
14%
12%

Details

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