The Phi Phenomenon, The Optical Illusion That The Brain Creates

The phenomenon phi (φ) is an optical illusion that our brain generates by making us believe that a fixed figure is in motion. The Gestalt school, in fact, defined and coined this term in 1912, serving in turn to demonstrate something important: perception goes beyond our senses, beyond what we see or feel. Actually, it is a mere interpretation of our brain.

The subject is undoubtedly much more interesting than it may seem to us. These types of images call our attention to all of us, where striking figures of the most diverse shapes and colors seem to tremble, move, oscillate timidly before us … Knowing that this movement is not real supposes a small impact that forces us to question several things .

Thinking that the perceived stimulus does not correspond to the real stimulus makes us think at first that something is wrong with us. Are our senses? Is it a vision problem? Not at all, when it comes to the phi phenomenon and optical illusions, everything is fine with us.  

However, as the American neuroscientist David M. Eagleman, author of books such as Incognito, the secret life of the brain, points out, the first lesson we must learn about our senses is that we should not trust them. The simple fact of seeing something with our eyes does not mean much less that that something really exists.

The brain interprets, builds and rebuilds, invents and introduces axioms in our mind just to try to make something have a certain logic when it perceives, for example, that there are flaws or gaps in what it is seeing through our eyes. This type of discovery, in fact, was key to the development of Gestalt.

The phi phenomenon (φ), the pillar of Gestalt

It was Max Wertheimer (1880-1943) founder of the Gestalt School who first described the so-called phi phenomenon in the field of science. He did so through a study entitled Experimental Studies on the Perception of Motion (1912) with which to lay the foundations of the psychology of perception.

Thus, and as in most discoveries , chance led Dr. Wertheimer to find a stroboscope at a train station. After that curious finding, he wondered what created this fascinating phenomenon. He knew that this game of geometric figures was not in motion. Yet his eyes told him that it was so. He called that fact ‘ phenomenon φ’ , to distinguish it from β (beta), where a stimulus does have a real and logical ability to move.

Something was happening in such figures and Dr. Wertheimer wanted to understand what caused it.

Phi phenomenon and false movement, a mistake of the brain?

The phi phenomenon differs in several respects from classical optical illusions. To begin with, what there is generally is a succession of similar figures. They are still images; However, if these images are reproduced before our eyes one by one and at a certain speed, we will have the sensation that they are moving, when in reality, they are not.

• Max Wertheimer showed that if we show a succession of static images at a specific speed, our brain interprets it as something that is in motion.
• This phenomenon is in turn related to retinal persistence. This concept is based on the idea that images remain ‘imprinted’ on our retina for a small fragment of a second. If we pass many images before the human eye quickly, the brain will not be able to differentiate one figure from the other in isolation.

• This means that it ends up interpreting (wrongly) that it is the same object in motion.  

It should be noted that this research by Max Wertheimer and his theory of the phi phenomenon contributed to the development of cinema, with the classic stills succeeding one after another. In fact, it would be Hugo Münstenberg who became interested in this idea to give it shape in 1916.

The phi phenomenon , the starting point for the Gestalt school

Importantly, the Phi phenomenon was not Max Wertheimer’s innovation to the world of scientific psychology. In fact, within the field of photography this type of perceptual experience was already known. In fact, one of the best known exponents was the British photographer Eadweard Muybridge (1830-1904).

His work was groundbreaking for its time. We were in 1878 and Muybridge had already invented what he called chronophotography. One of his best known works was photographing the movements of a horse and its rider during a race thanks to the use of 24 cameras lined up on the track. After obtaining and developing the images, he knew that exposing them at a certain speed generated real movement.

Now, while for some this phenomenon was not something new, for the Gestalt field Wertheimer’s work was an effect that changed everything. We cannot forget that this school of psychology laid the foundations for the study of sensation and perception. For theorists like Wertheimer himself as well as for Wolfgang Kohler or Kurt Koffka, what we perceive are not isolated stimuli.

In reality, the brain always tends to group everything we see, to create a whole governed by a sense of coherence and an interpretive logic. Hence, for example, he chooses to think that this succession of images are not isolated figures, but the same moving object. Understanding it this way saves effort, it’s easier.

However, and here comes the problem, it is not something real. As the neuroscientist David M. Eagleman says, it never hurts not to trust 100% in everything that the brain makes us believe …