Science

The Best Visual Illusion of the Year

That’s "The Leaning Tower", winner of the Neural Correlate Society’s third annual Visual Illusion of the Year contest. How does it work? The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more, as if photographed from a different angle. The reason […]

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That's "The Leaning Tower", winner of the Neural Correlate Society's third annual Visual Illusion of the Year contest. How does it work?

The two images of the Leaning Tower of Pisa are identical, yet one has the impression that the tower on the right leans more, as if photographed from a different angle. The reason for this is because the visual system treats the two images as if part of a single scene. Normally, if two adjacent towers rise at the same angle, their image outlines converge as they recede from view due to perspective, and this is taken into account by the visual system. So when confronted with two towers whose corresponding outlines are parallel, the visual system assumes they must be diverging as they rise from view, and this is what we see.

The top 10 finalists are here. My favorites: the Drifting Background and 'Weaves' and the Hermann Grid.