Phi phenomenon

The phi phenomenon is an optical illusion in which apparent motion can be observed when stationary images are presented in succession at a high frequency. When the phi phenomenon is observed in action, a shadow of sorts that is almost the same color as the background seems to appear in front of and briefly occlude the stimuli. In some respects, this illusion is similar to the closely related beta movement optical illusion, though the stimuli do not appear to move as with that particular phenomenon. The phi phenomenon was first described by Austro-Hungarian psychologist Max Wertheimer in 1912. His work on the subject gave birth to a school of psychological thought called Gestalt psychology. In Wertheimer’s broad explanation of the illusion, he described phi phenomena as including all forms of apparent movement that occur when two nearby optical stimuli are presented in alternation. By this definition, beta movement would be considered one of the phi phenomena.

Background

The roots of the phi phenomenon are closely tied to Max Wertheimer and his creation of Gestalt psychology. Wertheimer was a psychologist from Prague, then part of Austria-Hungary, who eventually co-founded the school of Gestalt psychology alongside fellow thinkers Kurt Koffka and Wolfgang Köhler. Born in 1880, Wertheimer initially studied law before turning his attention to philosophy and psychology. Upon earning a doctorate degree from the University of Wurzburg in 1904, Wertheimer embarked on an academic career.

Wertheimer’s biggest breakthrough came after he noticed that flashing lights he saw at a train station appeared to create the illusion of movement. This observation led him to undertake an in-depth study of perception. Wertheimer eventually came to call the illusion he observed at the train station the phi phenomenon.

During the time he spent working at the University of Frankfurt’s Psychological Institute, Wertheimer met Koffka and Köhler. Together, the three men laid the groundwork for what would become Gestalt psychology. Gestalt psychology is a psychological school of thought that focuses on the human mind and examines behavior as a whole. The fundamental point of Gestalt psychology is that human beings do not simply focus on every small detail when attempting to make sense of the world around them. Rather, Gestalt psychology suggests that humans instead typically view objects as part of a greater whole and elements within a more complex system. In practice, Gestalt psychology was significant because of the important part it played in the development of the modern scientific understanding of human sensation and perception. Although Gestalt psychology has since been incorporated by other psychological fields, its influence was significant and its legacy remains intact.

After introducing the phi phenomenon and helping to launch Gestalt psychology in 1912, Wertheimer continued his prestigious career. When the political situation in Europe became untenable thanks to the rise of Adolf Hitler and the Nazi Party in Germany, Wertheimer immigrated to the United States. There he spent the last ten years of his life teaching and studying at the New School for Social Research in New York. With Wertheimer at the helm, the New School eventually emerged as one of the world’s leading schools of psychology. Wertheimer died of a heart attack on October 12, 1943.

Overview

The road to explaining the phi phenomenon began when German psychologist Wilhelm Wundt founded the world’s first scientific psychology laboratory in 1879. Wundt and his associates subsequently created the structuralism approach. This approach defined perceptions as a combination of elements known as sensations. In response to stimuli, these sensations group together to form an image or object that the human observer perceives. This explanation of perception remained the standard in psychology for decades and laid the foundation for Gestalt psychology.

Based on the idea that the whole is different from the sum of its parts, Gestalt psychology suggested an alternative explanation of perception. Rather than accepting that perception was built up from sensations, it described perception as the end result of perceptual organization. Wertheimer took his first step towards coming to this conclusion when he bought a stroboscope at a German train platform. A stroboscope was a mechanical toy that created the illusion of movement by rapidly interchanging two slightly different images. Wertheimer wondered if the stroboscopic movement he observed was caused by sensations and whether Wundt’s structuralism could explain the phenomenon.

The phi phenomenon is an optical illusion that leads an observer to perceive apparent movement in objects that are actually stationary. In short, it happens when a person views a succession of stationary images and perceives motion that is not actually occurring. As Wertheimer explained, this illusion takes place when the brain attempts to fill in the information it incorrectly thinks is missing between successive images.

The phi phenomenon is a visual illusion that occurs thanks to what is known as first-order motion perception. One of the two main ways the human brain perceives movement, first-order perception is precipitated by special neurons in the retina that track motion through luminance. These neurons detect a change in luminance at one particular point of the retina and correlate it with a similar change at another nearby point. In the case of the phi phenomenon, first-order motion leads a series of regular luminous impulses that are perceived as a continual pattern of movement.

The phi phenomenon is the main underlying principle that explains how movies work. At a movie theater, the audience is shown a rapid succession of still frames at a high rate of speed. Although the images themselves are not actually moving, they are displayed one after another so quickly that seems like they are because the audience’s brains are filling in the gaps between the frames and producing the perception of motion because of the phi phenomenon. This process is also aided by beta movement, which is another optical illusion closely related to the phi phenomenon. In beta movement, which Wertheimer described as one of a broader range of phi phenomena, the brief projection of one figure and the subsequent brief projection of another similar figure in a different position creates the illusion of a single moving figure.

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