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10 Cool Optical Illusions

A Selection of Fun and Fascinating Illusions

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Optical illusions can be fun and fascinating, but they can also tell us a great deal of information about how the brain and perceptual system function. There are countless optical illusions out there, but here is a sampling of some of the most fun and interesting.

1. The Hermann Grid Illusion

The Hermann Grid Illusion
Rob Patrick Robpatrick/ Flickr CC
Sometimes we see things that aren't really there, and the Hermann Grid illusion is a great example of this. Notice how the dots at the center of each intersection seem to shift between white and gray? Like many optical illusions, different theories have been proposed to explain exactly why this happens.

2. The Spinning Dancer Illusion

Spinning Dancer Illusion
Nobuyuki Kayahara
The popular illusion made the rounds on blogs and websites a few years ago, supposedly as a test to determine if you are "left-brained or right-brained." In reality, the illusion occurs because our brains must attempt to construct space around the spinning figure.

3. The Ames Room Illusion

Ames Room
Image courtesy Mosso - http://www.flickr.com/photos/39325045@N00/355613728/
Would you be surprised to learn that the two people in the image at the left are actually the same size? Learn more about how this classic illusion works and how the effect has been put to use in special effects such as in the movie The Lord of the Rings.

4. The Ponzo Illusion

Ponzo illusion
Image from Wikimedia Commons
When you look off into the distance, objects seem closer together as they become further away. For example, the outside borders of a road or railroad appear to converge as they recede into the distance. The Ponzo illusion involves placing two lines over an illustration of a railroad track. Which line is longer? In reality, they are exactly the same length. Learn more about how this fascinating illusion works

5. The Zollner Illusion

Zollner Illusion
Fibonacci
Sometimes the background of an image can interfere with how your brain interprets the image itself, as is the case with the Zollner illusion. This is one illusion that can actually make a viewer start to feel slightly queasy if you stare at it for too long!

6. The Kanizsa Triangle Illusion

Kanizsa Triangle
Image from the Wikimedia Commons
According to the Gestalt law of closure, we tend to see objects that are close together as a related group. In the case of the Kanizsa Triangle, we even see contour lines that don't exist and ignore gaps in order to form a cohesive image.

7. The Muller-Lyer Illusion

Muller-Lyer Illusion
Image by Fibonacci / Wikimedia Commons
Here's a classic illusion that still manages to stump a lot of people. Which line is longer? Actually, both lines are the same length. Surprised? Learn more about how the Muller-Lyer illusion works.

8. The Moon Illusion

Moon Illusion
If you've ever spent any time gazing up at the night sky, then you've probably noticed the moon illusion, in which the moon looks bigger on the horizon than it does higher up in the sky. Why does this happen? Many theories have been proposed, although there is no universally agreed upon explanation. Learn more about how the moon illusion works and some of the possible theories that have been suggested.

9. The Lilac Chaser Illusion

Lilac Chaser
Image by TotoBaggins/Wikimedia Commons
In the lilac chaser illusion, the viewer observes several different visual effects over the span of about 30 seconds. First described in 2005, the illusion is caused by a number of different factors including negative afterimages and what is known as Troxler fading. Check out the illusion yourself and learn more about how the lilac illusion works.

10. The Negative Photo Illusion

Negative Photo Illusion
Image by geloo, modified by Kendra Cherry
Here another fun example of negative afterimages that produce a startling result. In the negative photo illusion, your brain and visual system essentially take a negative image and turn it into a full-color photo. Check out the illusion to give it a try and learn more about how it works.

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