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
flagSpain
83%
8%
8%
0%
12
flagCroatia
75%
8%
8%
8%
12
flagFinland
73%
13%
6%
6%
15
flagthe Netherlands
68%
21%
0%
10%
19
flagthe United Arab Emirates
61%
0%
30%
7%
13
flagPakistan
58%
8%
16%
16%
12
flagGermany
56%
20%
13%
9%
87
flagCanada
54%
20%
16%
8%
24
flagthe Philippines
52%
11%
11%
23%
17
flagthe United States
50%
18%
18%
11%
341
flagNorway
50%
14%
21%
14%
14
flagFrance
48%
36%
12%
4%
25
flagPoland
46%
22%
18%
12%
6655
flagIndia
45%
27%
18%
6%
107
flagAustralia
45%
22%
22%
9%
22
flagthe United Kingdom
43%
19%
23%
11%
187
flagItaly
36%
22%
36%
4%
22
flagRussia
35%
28%
21%
7%
14
flagRepublic of Ireland
34%
13%
26%
26%
23
flagUU
30%
10%
50%
10%
10

Gender

men50%
women45%
red one
50%
45%
blue one
17%
23%
none of them
17%
17%
both of them
14%
12%

Details

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