Optical illusions are often puzzling, entertaining, and headache-inducing…but do you know what makes them so mystifying? Philosophers have been attempting to answer that question for centuries. This is the fascinating history behind optical illusions and how they trick our minds.

The earliest optical illusions

Theories about optical illusions date all the way back to ancient Greece. The Greeks often used optical illusions in their architecture and art. One of the earliest applications of optical illusions was found in Greek rooftops. On temples, roofs were built at a slant, yet observers believed that the rooftops were curved. The optical illusion that the roofs were bowed in baffled many of the Greeks. Understanding such illusions became a fascination of many philosophers. Some argued that our eyes play tricks on us, yet others decided it had more to do with the mind than the senses.

In 5 B.C., a Greek philosopher named Epicharmus decided to take a shot at explaining optical illusions. He theorized that our brains weren’t at fault and that they could perceive an image clearly. Instead, he thought that our senses betrayed us when viewing optical illusions. “The mind sees and the mind hears,” he said. “The rest is blind and deaf.”

Another Greek philosopher, Protagoras, thought the exact opposite. He didn’t believe that our eyes had anything to do with how we perceived optical illusions. Instead, he thought that optical illusions were dependant on the environment in which they were viewed rather than our senses. The crossroads at which these two philosophers found themselves became a massive, centuries-long conversation between philosophers, scientists, and psychologists. The next person to try to tackle the theory was Aristotle.

Aristotle, another Greek philosopher from around 350 B.C., decided that both Epicharmus and Protagoras could be correct. He thought that Protagoras made a great point about our senses: we rely on them for nearly every aspect of assessing reality. Therefore, it was hard to blame the distortions of reality on our five senses. However, Aristotle also commented that our senses aren’t terribly difficult to trick. Distortions such as thinking that a tall building is swaying or seeing water on a road as a result of heat waves are examples of sensory illusions. Another famed Greek philosopher, Plato, pitched in his two cents about the matter. He thought that our minds and our eyes worked together to establish the world, including optical illusions. It’s a widely accepted belief in the present. However, research on the nature of optical illusions has remained pertinent and fascinating throughout history.

Understanding the puzzling phenomenon

When it came to early, intensive studies of optical illusions, two of the most dedicated researchers were Johannes Mueller and J.J. Oppel. The 19th-century duo of psychologists took a fascination in understanding the way that people discerned optical illusions. As a result, they dedicated much of their lives to performing illusion studies, conducting research, and drafting numerous essays, articles, and books on the subject of optical illusions. They managed to publish 12 theories about optical illusions in their lifetimes, as well as producing an illusion of their own. With the help of German sociologist Franz Carl Muller-Lyer, they produced the illustrated Muller-Lyer illusion, helping the public to process and understand optical illusions.

In the same century, another German physicist was hard at work creating his own theories about illusions. Hermann von Helmholtz put forth a theory similar to Protagoras’. He introduced the concept of a cognitive illusion. He shared that these occur when our predetermined assumptions about our environment don’t line up with reality. Both our eyes and minds make inferences about our environment, and therefore, a cognitive illusion occurs our expectations regarding our prior knowledge about the world aren’t met. Four subtypes of cognitive illusions were established across the years: ambiguous illusions, paradox illusions, distorting illusions, and fiction illusions.

Ambiguous illusions occur when an image or object can be viewed in multiple ways which result in major appearance shifts. An example of this is the Rubin vase. On first glance, it appears to be an image of a vase. However, if you look a little closer, and you’ll see two faces holding the outline of the vase together. It’s difficult, if not impossible, to view both images at once. This is what makes it an ambiguous illusion. Paradox illusions occur when we are witnessing an image in which the circumstances are impossible. The work of M.C. Escher features paradox illusions, specifically when it comes to his sketches of staircases. In his piece “Relativity,” staircases twist and wind throughout the page, some upside down and sideways, yet each following the laws of physics on its own side. Such an image would be impossible to replicate in real life and can give observers a headache trying to imagine it, making it a paradox illusion.

Distorting illusions are those illusions which offer distortions of different variables regarding size, length, and shape. The Cafe Wall illusion is a great example of a distortion illusion. It consists of a pattern which resembles a checkboard that has been shifted with displaced rows. A fiction illusion is an illusion which exists entirely as a product of the mind that is only visible to one individual. People with schizophrenia experience these types of illusions. The emergence of Helmholtz’s theories seemed to explain a number of incredible optical illusions, yet research on the baffling subject didn’t stop there. The 20th-century produced some fascinating applications of illusions in the artworld.

Optical illusions in the 20th century

Back in 1915, cartoonist W.E. Hill produced one of the most famous optical illusions to date: “My Wife and My Mother-in-Law.” The famed sketch featured two women merged into one image. At one angle, the figure in the image is a very old woman looking off to the left of the page. However, upon closer inspection, you can see a young woman facing away from the observer. The ingenious illusion fascinated many, as the image that they first saw was due to the individual perception of each viewer.

In the 60s, 20th-century abstract artists took an interest in a new genre of art that they called “Op Art.” Op Art relied on abstract illusions such as hidden pictures, distorted patterns, vibrations and flashes, and other illusion-based artistic techniques incorporated into their paintings. It quickly became a popular and adored style in the artworld, and was practiced by famed painters such as Bridget Riley and Vasarely. Optical illusions became a major part of wider art culture.

To this day, philosophers, psychologists, and many more professionals continue to be amazed by the distortions produced by optical illusions. From philosophers in ancient Greece to present-day scientists and psychologists, researchers continue to be amazed by the phenomena of optical illusions.