The vertical line looks longer, but both lines are the same size Credit: S-kay/Wikimedia Commons Known as vertical-horizontal illusions, this specific illusion comprises a horizontal line with a ...

One such clever illustration is an optical illusion with horizontal lines. Line Illusions use surrounding colors/objects and our experience with perspective to use all our knowledge against us.

Peter Thompson and Kyriaki Mikellidou, The 3-D Helmholtz Square illusion: more reasons to wear horizontal stripes, Journal of Vision, August 5, 2009 vol. 9 no. 8 article 50.

Humans are a less extreme version of this; if you grow up in an environment with a lot of vertical lines like, say, a city, you’re going to have more trouble distinguishing horizontal lines, and ...

Peter Thompson and Kyriaki Mikellidou, The 3-D Helmholtz Square illusion: more reasons to wear horizontal stripes, Journal of Vision, August 5, 2009 vol. 9 no. 8 article 50.