And the best visual illusion of the year is…


…the Leaning Tower Illusion, by Fred Kingdom, Ali Yoonessi and Elena Gheorgiu of McGill University.

The two images…are identical, yet one has the impression that the tower on the right leans more…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 illusion is not restricted to towers photographed from below, but works well with other scenes, such as railway tracks receding into the distance. What this illusion reveals is less to do with perspective, but how the visual system tends to treat two side-by-side images as if part of the same scene. However hard we try to think of the two photographs of the Leaning Tower as separate, albeit identical images of the same object, our visual system regards them as the ‘Twin Towers of Pisa’, whose perspective can only be interpreted in terms of one tower leaning more than the other.

See the other entries in The Best Visual Illusion of the Year Contest.


3 thoughts on “And the best visual illusion of the year is…

  1. Human brain is incredible, espasially when interpreting images. 🙂
    The only downside of this is that most of people don’t use their brains.
    Great illusion 🙂

  2. I’m curious why one tower appears to lean to the right, rather than the other appearing to lean to the left or why they don’t both appear to lean away from each other to an equal degree.

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