The Checker Shadow Illusion

In the picture, there is one square marked A and one marked B. At first glance, your visual system will determine square B to be a lighter color than square A, when, in fact, they are the exact same color. How does your visual system get tricked into thinking this?

The first part of the trick has to do with the squares around square B. Even though it is in shadow, square B is still lighter than its four neighboring squares. Therefore, even though square B is dark, it is light when compared to its neighbors. Outside of the shadow, the dark squares are surrounded by lighter squares. This makes them look darker in comparison to the square in the shadow.

In general, shadows have soft edges while objects like the squares have sharp objects. In order to avoid being misled by shadows, the visual system does not pay attention to gradual changes light level. Because square B is surrounded by dark squares, the visual system determines that all of B’s edges should be sharp edges, thus coming to the conclusion that its edges should be seen as changes in color rather than a change in light or shadow.

This optical illusion tells us that the visual system does not succeed at being a physical light meter. It generalizes visual information, takes what it has, and allows us to see the world in a way that is not always correct.

As you can see in the picture below, the two squares are definitely the same color:

3 responses to “The Checker Shadow Illusion”

  1. Whitney Grace Wilson says:

    This is the original illusion that I had wanted to do, but couldn’t find enough information on. I find it very interesting how our brain deciphers illusions such as this incorrectly. The fact that the effect of the shadow throws it all off is what I find so interesting.

  2. Grace Frost says:

    It definitely took me a while to accept that squares A and B were the same colour! The reasoning behind this illusion is fascinating.

  3. Brianna Margaret Cathey says:

    This illusion sure does make out brain seem very limited in the visual system’s capacity to perceive something as reality. I too had a difficult time accepting that A and B were the same color but when I covered up the squares around B I could see it. I didn’t know that the edge of the square would have such large impact on how we perceive the image.

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