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 Netherlands
64%
24%
0%
12%
25
flagthe United Arab Emirates
62%
6%
25%
6%
16
flagPakistan
61%
7%
15%
15%
13
flagGermany
60%
18%
13%
7%
108
flagCanada
54%
20%
16%
8%
24
flagthe United States
51%
18%
17%
11%
355
flagthe Philippines
50%
11%
16%
22%
18
flagPoland
46%
22%
17%
12%
7092
flagIndia
46%
26%
18%
7%
113
flagItaly
46%
21%
28%
3%
28
flagFrance
46%
34%
15%
3%
26
flagNorway
46%
13%
20%
20%
15
flagAustralia
45%
22%
22%
9%
22
flagthe United Kingdom
44%
19%
22%
11%
203
flagUnknown
42%
11%
34%
11%
26
flagRepublic of Ireland
40%
14%
22%
22%
27
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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