Phi Phenomenon, the Optical Illusion Created by the Brain

The phi (φ) phenomenon was key to Gestalt. This optical illusion that makes us believe that fixed images are moving, shows us to what extent our brain can make us believe realities that are not entirely true.

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The phi phenomenon (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. All of us are struck by this type of images 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 is a small impact that forces us to question several things .

To think that the perceived stimulus does not correspond to the real stimulus makes us think at first that something is not right in us. Are our senses? Is it a vision problem? Not at all, as far as the phi phenomenon and optical illusions are concerned, everything is fine with us.

However, as pointed out by the American neuroscientist David M. Eagleman, author of books such as Incognito, the secret life of the brain, 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, constructs and reconstructs, invents and introduces axioms in our mind just to try to make something logical when it perceives, for example, that there are faults or gaps in what it is seeing through our eyes. This discovery type, in fact, was key to the development of Gestalt.

“The whole is greater than the sum of its parts.”

-Max Wertheimer-

The phenomenon phi (φ), the pillar of the 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 caused Dr. Wertheimer to find a stroboscope in a train station. After that curious discovery he wondered what created this fascinating phenomenon. I knew that this game of geometric figures was not in motion. However, his eyes told him that this was the case. He called that fact ‘phenomenon φ’, to distinguish it from β (beta), where a stimulus does have a real and logical capacity to move.

In that type of figures something happened and Dr. Wertheimer wanted to understand what produced it.

The phi phenomenon and the false movement, a brain error?

The phi phenomenon differs in several aspects of the classic optical illusions. To begin with, what there is usually 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 feeling that they are moving, when in reality, it is not so.

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 related in turn to the retinal persistence. This concept is based on the idea that images remain ‘printed’ on our retina during a small fragment of a second.

If we pass many images before the human eye quickly, the brain can not differentiate in isolation one figure from the other.

This causes me to end 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 photograms happening one after the other. In fact, it would be Hugo Münstenberg who was interested in this idea to shape it in 1916.

The phi phenomenon, the starting point for the Gestalt school

It is important to emphasize that the Phi phenomenon was not an innovation of Max Wertheimer to the world of scientific psychology. In reality, this type of perceptive experience was already known within the field of photography. In fact, one of the best-known exponents was the British photographer Eadweard Muybridge (1830-1904).

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

Now, while for some this phenomenon was not something new, for the Gestalt field the work of Wertheimer was an effect that changed everything. We can not 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.

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, that choose to think that this succession of images are not isolated figures, but the same object in motion. Understanding it like that saves effort, it’s easier.

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