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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Answers by country
red one
blue one
none of them
both of them
answers
Switzerland23
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the United States356
India160
the United Kingdom134
the Philippines16
Germany303
Canada21
Republic of Ireland19
Poland14094
Ukraine153
Austria57
Unknown22
Belarus28
France13
Russia141
Greece21
Kazakhstan21
Australia26
Uzbekistan14