Ask A Scientist

How do optical illusions make you see things differently? 

Asked by: Priscilla Williams
School: St. John the Evangelist
Grade: 5
Teacher: Anu Rai
Hobbies/Interests: Soccer, lacrosse 
Career Interest: Oral surgeon 

 

Answer from Peter Huang

Assistant Professor of Mechanical Engineering

Research areas: Fluid mechanics, Optical diagnostics, biotechnology
Interests/hobbies: Karate, cooking

The visual scenery that comes into your eyes is like a picture that you take with your smartphone. Somebody has to examine the picture and interpret the information in the picture, such as what is in it, how big the objects are, where the objects are, etc. This somebody is your brain. Your brain functions like a supercomputer that processes all of the visual information and makes sense of what is in front of you. This, of course, has to be done super fast, given that new information comes into your eyes constantly. Over evolutionary time, our brains have developed guidelines, or shortcuts, to use information such as color, brightness, contrast, pattern, relative size, shape, etc., as well as memory and experience, to interpret images as fast as possible. Under most circumstances, your brain does an excellent job and forms an accurate understanding of the physical reality.

Optical illusions exploit some of the weaknesses or deficiencies of these inherent guidelines that your brain naturally follows, thus giving you a distorted perception. They trick our brains into make either false or conflicting interpretations of the image in front of us. Perhaps the most famous example is Rubin’s Vase. Depending on your internal guidelines, you may see the image as a vase in the middle or as two faces on the sides. Another common example is the barber pole illusion, which reveals our brains’ bias in predicting the direction of an object’s continuous motion. The subject of optical illusions has been intensely researched by psychologists and cognitive scientists, who have developed various theories explaining the many different types of optical illusions that can trick our brains.

Sometimes we are able to train our brains to follow new guidelines, much like the way we learn math in school. Examples of such training include the viewing of autostereogram and Anaglyph 3D abstract art. Other times, these perception guidelines are ingrained into our unconsciousness and are difficult to break. My favorite example is the Spinning Dancer. Some people see the dancer spinning clockwise, while others see her spinning counter-clockwise, or both. I personally see her spinning counter-clockwise, and no matter how hard I try, I could not force my brain to make her turn around. It just shows that when it comes to optical illusions, we don’t always get to see what we want to see.

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Last Updated: 9/25/14