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
the Netherlands15
the United States356
India160
Republic of Ireland18
the Philippines16
Germany300
the United Kingdom133
Canada21
Poland14086
Ukraine153
Austria57
Unknown22
Belarus28
France13
Russia141
Greece21
Kazakhstan20
Australia26
Uzbekistan14