8 Optical Illusions You Can Find Online, Because They're Super Entertaining
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If you were anything like me as a kid, you spent hours browsing through books of optical illusions to see what kind of tricks you could play on your brain. Even as an adult, they're still weirdly fascinating. The most obvious example, of course, is the infamous dress that divided the Internet last year; some people thought it was white and gold, and others were totally wrong. But there are optical illusions all over the place, and according to a study published in Psychological Science last month, your peripheral vision might be responsible for more of them than you'd think.

In the study, researchers presented 20 participants with a series of images and asked them to focus on the center of the screen, where an image would appear before a different one would fade in on the sides of the screen. Over time, researchers found that the perception of the peripheral image would change to match the one in the center, so the screen appeared uniform even though it wasn't.

Our findings show that, under the right circumstances, a large part of the periphery may become a visual illusion. ... Perhaps our brain fills in what we see when the physical stimulus is not rich enough," said lead author Marte Otten in a Psychological Science blog post. Basically, participants' brains were reconstructing their peripheral vision based on an educated guess. It's not a problem most of the time, but you can see how it would lead to seeing things that aren't there — or not seeing things that are there.

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So what does the illusion used by researchers look like? You can watch it below, along with some other personal favorites you can find online. Have fun questioning reality!

1The Uniformity Illusion

Marte Otten on YouTube

This is the illusion researchers used in their experiment. You can find plenty of information about the Uniformity Illusion here, but here's how to watch the video: Put the video on full screen, and sit about a foot and a half away. Focus your eyes on the center of the image, and blink as little as possible. The time it takes to work depends on the person, but according to the Uniformity Illusion website, it could take up to a few minutes.

2The Muller-Lyer Illusion

Kelvin Wong on YouTube

As you can see in the video above, the two arrows appear to be different lengths, but they're actually the same. Created by psychiatrist Franz Muller-Lyer in 1889, the Muller-Lyer Illusion is understandably famous for its insight into depth perception.

3Kanizsa's Triangle

Wikimedia Commons

Do you see a white, upside-down triangle in the picture above? If so, you're falling prey to Kanizsa's Triangle

4Duck-Rabbit Illusion

Wikimedia Commons

Does the picture above illustrate a duck or a rabbit? The answer is both, but the catch is that you can only see one at a time.

5The Simultaneous Contrast Illusion

Wikimedia Commons

You probably perceive the bar in the center of the image as progressing from light to dark gray. In reality, it's the same color — the background is the only gradient in the picture.

6The Spinning Dancer Illusion

GAMS1981 on YouTube

The girl featured in this illusion can be perceived as spinning either clockwise or counter-clockwise. The coolest part? Most people see her switch directions after a few moments of watching.

7The Ebbinghaus Illusion

Wikimedia Commons

Like the aforementioned Muller-Lyer Illusion, the Ebbinghaus Illusion shows two objects that appear different sizes but are actually the same. In this case, it's the orange circles; although the left one looks smaller, they're the same size.

8The Cafe Wall Illusion

Wikimedia Commons

The lines in this image should appear sloped, but if you look at them individually, they're actually parallel. Brains are weird.