Take a look at the square on the left side of the photo above. Does the color of tile A appear darker than the color of tile B? It turns out that both tiles are the same color. Don’t believe me? Look at the square on the right side to what happens when they are merged.

This illusion, the brainchild of Edward H. Adelson, PhD, from the Massachusetts Institute of Technology’s Perceptual Science Group, throws our perception into question. It may leave us wondering: Can we truly trust our senses? After all, our brains are constantly bombarded with information from our senses, so can we trust what we perceive as an accurate reflection of reality? Optical illusions are just one of the many ways to show that our brain is biased and that it can easily be exploited by loopholes in our visual processing.

But our brains are smart. They don’t simply receive images from the eyes. The brain takes in the electrical signals that turn into images and combines them with information from our past experiences and expectations, constructing them into a meaningful scene. This automatic processing allows us to recognize familiar objects, perceive depth and motion, and so much more. Although our brains are smart, they are not foolproof, and they can be tricked by optical illusions.

The reason most people fall for this illusion is because it fools our brain’s automatic processing of color. We don’t simply perceive color alone, but also how color compares to its surroundings. This is a concept called simultaneous brightness contrast. That means, in the example above, the light-colored tile in the shadow is surrounded by darker tiles, making it appear lighter relative to them.

Our brain also tries to perceive the shadowed area as a single shaded surface. This combined effect makes the shadowed light tile appear much lighter than the unshaded dark tile, even though they are the same color.

Of course, this is just one example of an optical illusion. There are plenty more that exploit different aspects of our brain and how it processes sensory information. This checker shadow illusion serves as a reminder that our senses aren’t always perfect and that a healthy dose of skepticism can be helpful when interpreting the world around us.