The Leaning Tower Illusion



The Leaning Tower Illusion

Two identical pictures of the leaning tower of Pisa are displayed side by side. The towers are parallel. However, it seems that the picture on the right is leaning more than the picture on the left. Rather than looking parallel, the two towers seem to diverge farther apart in the distance. The explanation for this illusion lies in how our visual system interprets depth. We have 2-dimensional eyes, but we need to interpret 3-dimensional space, so our brain has to makes sense out of a distorted picture sent by the retina.

When our retina sees two parallel lines going off into the distance, the lines appear to converge. For instance, stand in the middle of a road and look down the road. The left and right edges of the road seem to converge in the distance. So, when our visual system sees two lines converging in the distance, our brains are hard-wired to interpret them as parallel. In the case of this illusion, our visual system sees two lines (towers) that look like they DON’T converge in 3-d distance. Thus, our brains actually interprets that these towers are diverging apart.

This illusion demonstrates how our brains have evolved to understand 3-dimensional space. Understanding space is crucial to navigating around an environment in search for food and whatnot. Thus, we are able to understand and sense depth in a 2-d image provided by the retina. When we see converging lines, our brains interpret the visual distortion and think parallel. However, this also means we can be tricked. The leaning towers are 2-d but they look 3-d. That causes the illusion to occur.


3 responses to “The Leaning Tower Illusion”

  1. Carlos Aizenman says:

    That’s really cool, could you add/link the source for your image?

  2. Whitney Grace Wilson says:

    This is such a cool situation! I had never heard of this before. We have all seen the sides of the roads converging, but I don’t think I’ve ever seen something “diverge” like this before.

  3. Dhruv Mohnot says:

    Whoa, this is quite interesting. I’ve never encountered this type of illusion before. I wonder if artists make use of this illusion to depict converging or diverging lines.

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