Optical Illusions: When Your Brain Can't Believe Your Eyes

There are other real-world examples of illusions. Pilots might encounter visual illusions while in flight, such as a false horizon, or when landing, such as a narrow runway. They are trained to recognize and ignore these illusions so they can safely fly their aircraft.

But while some illusions may pose a safety threat, others may actually be used as safety measures. On Chicago's Lake Shore Drive, for example, visual illusions have been used to control drivers' speed on a hazardous curve. Stripes on the road are painted closer together as drivers approach the sharpest part of the curve. The illusion makes drivers think they're speeding up -- so they slow down and, it's hoped, have fewer accidents.

Illusions can offer scientists new insights on how vision and the brain work -- and are more than intriguing parlor tricks.

"They widen the mental horizons and make it clear that things are a little different than they seem," Bach said.

Visual illusions are not just some nice puzzle, like a crossword, or an entertainment feature, said Martinez-Conde. "They're important tools in visual research to help us understand how visual processing works in the normal brain and also in the diseased brain."

Beyond their amusement value, one researcher speculated that illusions may also serve an evolutionary purpose.

Seeing the 'Future'

"The brain is always constructing things, which is helping you survive. Some of these constructions can be fiction," said Mark Changizi, a neurobiologist and assistant professor of cognitive science at Rensselaer Polytechnic Institute in Troy, N.Y.

Changizi came up with a theory to help explain why we see illusions. He argued that illusions are due to the brain's attempt to "see" the future. They occur during the slight time lag after light reaches the retina in your eye, but before your brain translates it into a visual perception.

According to Changizi, author of "The Vision Revolution," when the brain attempts to generate a perception, it basically is taking a guess at the near future by trying to fast-forward a tenth of a second. As a result of this "neural delay," you might not be perceiving an image as it actually is, but as you expect it might soon be.

"Illusions occur when the brain attempts to perceive the future, and those perceptions don't match reality," he said.

Although there is no single reason illusions take place, Martinez-Conde offered another possible explanation.

The brain is a limited structure with limited resources, including its number of neurons, wires, and neuronal connections, she suggested. "So in some cases, illusions may be due to the brain's need to take shortcuts." Simply put, the brain might need to quickly give more importance to some features in a visual scene than others.

Recognizing the Best Illusions of the Year

Color, motion, shape and the amount of light that hits your eye are just a few of the factors that might cause you to see an illusion.

Some people like to design new illusions and, in fact, there is an annual international contest to recognize the best -- and most novel -- visual illusion of the year. First place this year went to an entry called "The Break of the Curve Ball," which depicted the path of a spinning disk and helped illustrate why the abrupt shift of this pitch is so good at fooling baseball hitters.

No doubt, the lessons learned from illusions extend beyond the baseball diamond -- and deep into your mind.

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