Phi Phenomenon (Optical Illusion Effect)

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Gestalt Theory is more than just a school within psychology. It provides the secrets behind optical illusions. Gestalt Theory is studied not just by psychologists, but also by web designers, artists, and marketers.

As a whole, Gestalt looks at the ways that the human mind perceives patterns over the individual components within said pattern. These patterns trick us. We see movement on flat surfaces and our mind creates images that don’t actually exist. But we can break down Gestalt Theory into individual phenomena and ideas that form the larger picture, like the Phi Phenomenon.

What Is the Phi Phenomenon?

The Phi Phenomenon is the apparent motion of two stimuli that are presented to a viewer in rapid succession. If two boxes are placed next to each other, and each individual box is shown very quickly, the whole image appears to move. Arguably, this discovery kickstarted the entire Gestalt movement. 

By understanding this one idea, we can begin to break down the images, movement, and  larger pictures that our mind draws from individual pieces.

Phi Phenomenon Examples  

Classic examples of the Phi Phenomenon are typically limited to two objects moving back and forth. The movement within the phenomenon is not the objects themselves, but the whole image. When you watch images of three red circles moving in succession, you may perceive that the three red circles are “in motion.” When we perceive the stimuli itself moving, it’s a different type of motion than the motion described by Wertheimer as “Phi Phenomenon.” Confused? You’re not alone. There isn’t much literature on the distinctions between different types of objectless movement.

While the classic example has remained the same since the 20th century, Max Wertheimer has used Phi and Phi Phenomena as umbrella terms to describe all types of objectless movement. This includes beta movement.

Examples of Objectless Motion

One of the most well-known examples of objectless motion in the modern world is that of the solid circles placed in a circular pattern. In one image, one of the solid circles is removed. In the next image, the solid circle is replaced, and the circle next to it is removed. So on and so forth. When these images are played in rapid succession, it looks as though the circle is moving. Similar images are often displayed as we wait for our computers to turn on or for videos to load.

DIY Objectless Motion

We can create objectless motion, or “pure phi,” using just a pen and a few sheets of paper. Have you ever watched a moving picture on a flip book? Maybe you created your own flip book, using the corner of a Post-It Note. Flipbooks allow you to look at a series of similar images in rapid succession. It gives you the illusion that a car is moving, a stick figure is jumping, or that any image is working.


While the Phi Phenomenon was given its name in 1912, it has a history much longer than that. Artists, engineers, and toymakers have been incorporating this phenomenon into products for centuries. Take the Zoetrope. We can actually thank the Zoetrope for flipbooks.

The Zoetrope is a toy shaped like a wheel. Each “spoke” of the wheel is a different image, much like the individual images you would put in a flip book. As you spin the wheel, the image appears to be moving. Although historians credit the invention of the Zoetrope to William Horner in the early 1800s, similar bowls and lamps with “moving images” date back to ancient Iran and China.

The Zoetrope is also credited as the predecessor to animation as we know it today.

How Was the Phi Phenomenon Discovered?

If it weren’t for Zoetropes, we might not have Pixar and beloved animated films. If it weren’t for the discovery of the Phi Phenomenon, we might not have Gestalt Theory. Max Wertheimer, along with his colleagues Wolfgang Köhler, and Kurt Koffka, are considered the founders of Gestalt Theory. (As Max Wertheimer first “discovered” the Phi Phenomenon, he showed Köhler and Koffka the classic image of black boxes that we use to describe the Phenomenon today.)

At the time, Wertheimer was not thinking about computers or animated movies. He believed that Gestalt Theory could help people better understand ethics, truth, and the roots of human behavior. Although Phi Phenomenon and other Gestalt principles have taken on other uses, we can still apply the theory’s original principles to its intended uses. Gestalt Theory describes the way that humans perceive that the whole is greater than the sum of its parts.

How can we break down images and ideas to see each individual part, instead of the moving whole? This is a central question of Gestalt Theory and Gestalt Therapy.

Reference this article:

Practical Psychology. (2020, July). Phi Phenomenon (Optical Illusion Effect). Retrieved from

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