Illusions

A Table Optical Illusion

Yes, those tables really are exactly the same, but it's almost impossible to understand that when you look at them. The problem is... your brain. Specifically, your "perceptual set," which helps you interpret visual data.

Why Do They Look So Different?

Here's the thing. The tabletops — the two, two-dimensional parallelograms on your screen — are identical. You can measure them. You can also watch this hynotic animation. You see them as different sizes, though, because you instinctively imagine them as part of three-dimensional tables, because of the the table-legs and the shading. This creates the optical illusion that the lefthand table is longer, and stretches off into the distance. First published in Roger Shepard's Mind Sights in 1990, this illusion is an example of a phenomenon called "size-constancy expansion."

So I Can't Trust My Own Eyes?

Not really. What you see is heavily influenced by what's going on in your brain — or, as psychologists put it, your "perceptual set." When you look at an image, what you see is affected by what you expect to see; what context the image appears in; your cultural milieu; and your feelings at the time. So, for instance: If you're listening to dreary music, hills look steeper.

Your "perceptual set" distorts the tables above (widely referred to as "Shepard's Tables") because you expect to see two-dimensional depictions of three-dimensional objects. That's normal, in our screen-heavy culture. It's almost impossible to break out of that mindset, and see the tabletops as the flat shapes they really are. Your "perceptual set" can distort  (or enhance!) other images, too, not to mention data from your other senses four senses.

It's not that your eyes are lying to you, though. It's just that they bring in truly overwhelming amounts of visual data every millisecond, and your brain has to interpret it fast. Sometimes, it takes shortcuts to get the job done. Kind of relatable, no?

Key Facts In This Video

  1. See an optical illusion of two same-sized tables here: 03:07

Written by Curiosity Staff January 8, 2015

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