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.
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red one
blue one
none of them
both of them
answers

14

22

354

160

18

16

131

21

14045

294

153

57

27

22

13

140

21

20

26

13