Take a look at the image below. It's a black dot surrounded by bright bursts of color in a sporadic order. Now take a closer, harder, longer look. Focus on that dot in the middle of the image, and those colored blobs that were so bright a moment ago will slowly begin to fade out of view until all you're perceiving is a black dot alone on a blank white background. First, the lighter colors go, then all the rest. But, the second you even slightly shift your focus or blink your eyes, BAM, the colors pop right back into their original position. Honest, we didn't set you up with a sneaky GIF; this is your visual system doing exactly as it should.

This bizarre disappearing act works due to something called Troxler's effect. This phenomenon was discovered by 1804 by Swiss physician and philosopher Ignaz Troxler. You've probably seen several different optical illusions work because of this effect — you focus on one thing, and something off in your periphery starts changing. In the pastel example above, you notice the colors slowly fade away because, with all of your attention focused on the dot in the middle, your brain deems the other stuff unnecessary and unimportant.

With so many stimuli around us pretty much at all times, our brains have gotten really good at selecting where to maintain focus. Think about it: You probably stop actively smelling your perfume a few minutes after you spray it on, and you probably don't feel the socks on your feet after slipping them on in the morning. Our brains are primed to tune out unchanging stimuli. Why would your brain need to waste energy on those things?

In this illusion, you purposely hold your focus on the dot. But in real life, you don't notice those "color disappearing" moments because your eyes are making micromovements all the time, even if you're looking at one thing. You were probably tempted to jump your eyes off to the side once you noticed the colors start to melt away, right? That's natural — your eyes wanted to hop over and check on the thing that seemed to be moving.

"Illusions are part and parcel of who we are. They're literally part of our neural machinery," Susana Martinez-Conde, a professor at SUNY Downstate Medical Center, tells the Verge. "It's not a bad thing to want to question your reality a little bit."

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Want more illusions? Check out Al Seckel's "The Ultimate Book of Optical Illusions." We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.