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
71%
14%
7%
7%
14
flagthe Netherlands
68%
21%
0%
10%
19
flagPakistan
58%
8%
16%
16%
12
flagGermany
57%
20%
13%
8%
80
flagthe United Arab Emirates
54%
0%
36%
9%
11
flagCanada
52%
21%
17%
8%
23
flagthe Philippines
52%
11%
11%
23%
17
flagthe United States
50%
18%
18%
10%
327
flagNorway
50%
14%
21%
14%
14
flagPoland
46%
22%
18%
11%
6393
flagIndia
46%
27%
18%
5%
106
flagAustralia
45%
22%
22%
9%
22
flagFrance
45%
36%
13%
4%
22
flagthe United Kingdom
42%
19%
23%
12%
181
flagItaly
36%
22%
36%
4%
22
flagRepublic of Ireland
36%
13%
22%
27%
22
flagRussia
35%
28%
21%
7%
14

Gender

men50%
women45%
red one
50%
45%
blue one
17%
24%
none of them
18%
17%
both of them
14%
12%

Details

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