Who doesn't love optical illusions? They intrigue us by making us feel as though we can peek at another reality. Optical illusions use color, light, and patterns to trick and mislead the human brain. In turn, the brain tries to interpret an unknown visual phenomenon and make sense of how it fits in the surroundings. Understanding the nature of optical illusions and the intricacies of human visual perception will help you use them to your advantage and create remarkable visual compositions.

Jastrow Illusion

Curved elements are tricky. The lower arch appears to be larger than the one above, but your eyes may deceive you. This phenomenon is named after the American psychologist Joseph Jastrow, who discovered the illusion in 1889. There's no mutual agreement as to why it exists, but some scientists believe it has something to do with the difference in radius. The longer curve influences the shorter one and makes it look even shorter, and vice versa. Notably, some theories suggest that people with autism may not experience visual size illusions due to their excessive focus on details.

Müller-Lyer Illusion

This is the classic version of the Müller-Lyer illusion that tricks our brain and distorts perception. The segment with inward-pointing chevrons or arrow tails seems larger than the segment with arrowheads at its endpoints, while indeed, both segments are equal. Franz Müller-Lyer, a German psychiatrist, presented this illusion in the 1880s, and since then, the debates on this phenomenon have seen no end.

One theory suggests that the perception of this illusion varies with age. According to Swiss psychologist Jean William Fritz Piaget, age decreases the susceptibility to certain illusions (such as the Müller-Lyer illusion).

Other scientists have suggested that cultural and physiological factors may play a role in the individual perception of visual illusions. Growing up in an urban environment with a higher proportion of rectangularity makes children more susceptible to optical illusions like Müller-Lyer than children from rural regions.

Ebbinghaus Illusion

Our eyes can sometimes deceive us. For example, you'd probably say that the right inner circle is bigger, while actually, both circles are exactly the same size. This illusion is named after German psychologist Hermann Ebbinghaus. In 1901, Ebbinghaus discovered that a circle surrounded by smaller circles appears larger than exactly the same one surrounded by large circles. In other words, proximity influences how we perceive size. Interestingly, the illusion has a stronger effect on people from Japan than those from the UK, women than men, and social scientists than on mathematicians.

Ponzo Illusion

The illusion tracks back to 1913 when Mario Ponzo demonstrated for the first time that the perception of an element's size depends on the background behind it. Converging lines create the illusion of depth, and our brains deduce that the rectangle that is farther away from us must be larger — while in fact, both rectangles are the same.

Curiously, people from rural and non-Western regions are less susceptible to the illusion, as well as individuals with the larger size of the primary visual cortex — the area in our brain that processes visual information.

Lilac Chaser Illusion

The Lilac Chaser illusion occurs after staring at the cross for 10-20 seconds. In a while, you start seeing green dots chasing the lilac ones. Eventually, you may even notice how all the lilac dots disappear completely. This phenomenon is often referred to as the Pac-Man illusion because it reminds people of the Pac-Man game where a character needs to eat all the dots inside a maze.

The illusion illustrates the aspects of visual perception, when our brains automatically try to smooth out the changes between the images and create a sense of continuity and stability in the world around us.

There's no definitive explanation yet for how this unusual visual phenomenon works, although studies suggest it occurs not only in our eyes but partially in our brain too.Curiously, low contrast or blurry images make the effect stronger.

Poggendorff Illusion

The Poggendorff illusion gets its name from the German physicist Johann Poggendorff, who first explained this illusion in 1860. Although it seems like the black line on the left stretches into a purple line on the right, don't take the bait. The black line is actually lined up with the yellow one, while our brain misinterprets the depth of elements and distorts the perception. The magnitude of the effect increases as the interrupted line gets more vertical and the width of the interrupting segment grows.

Despite numerous studies, there’s still no consensus found about the Poggendorff effect, and it remains one of the most controversial of the geometrical illusions.

Munker-White Illusion

The yellow rectangles in both A and B sections are of the same color and brightness — crazy, right? The Munker-White illusion shows how our brain and eyes create different perceptions of brightness. The illusion is based on the Bezold Effect named after Wilhelm von Bezold. He was a meteorology professor from Germany who discovered that color might appear different depending on its surroundings.

The original version of this illusion uses black and white stripes that are partially replaced by gray rectangles. All grey bars are the same color and opacity. Their brightness depends on the brightness of the top and bottom border stripes.

You can use the Bezold Effect in your designs by playing around with the lightness and color of the foreground to see how it affects the background shapes.

Mach Bands

At first sight, it looks like a regular color palette. At a closer investigation, you may notice false shadows appearing where the sides of rectangles meet. This is called the Mach bands illusion, named after an Austrian physicist, Ernst Mach, who discovered it.

A popular theory links the Mach bands illusion to lateral inhibition. This is a phenomenon that occurs between retinal neurons when one neuron or sensory cell activates a neighboring neuron. Lateral inhibition makes us perceive the darker areas even darker, and the lighter areas appear much lighter.

Like other visual and perceptual illusions, Mach bands illusion helps scientists study the way the eye and brain process visual information.

Make sure to double-check for this illusion when pairing colors side-by-side.

Shepard Tables

Among these two tables, one seems long and narrow, with its longer dimension receding into the distance. The other looks almost square, and we assume it's because it's angled toward us. The surprising thing is that the parallelograms that represent the tabletops are precisely the same size and shape. Roger Shepard used this illusion to prove that our brains can't help but make 3D interpretations of 2D images. Together with Shepard's elephant, this illusion was first published in the book Mind Sights in 1990 by Stanford psychologist Roger N. Shepard.

Watercolor Illusion

The inner rectangles are indeed snow white but hide their true colors behind the watercolor illusion discovered by Baingio Pinna in 1987. In this illusion, a white area takes on a pale tint of a thin, bright-colored polygon that surrounds it. The only condition is that the colored polygon itself should be surrounded by a thin border of the complementary color. Orange and purple are the most common pair that produces the strongest effect.

This illusion has a stronger grouping effect than proximity and can be used to unite elements within colored boundaries.

The next time you encounter an optical illusion, take a moment to appreciate the complex interplay of visual cues and cognitive processes at work. By embracing these fascinating quirks of human perception, we can continue to evolve and refine our approach to design, creating more immersive and impactful visual experiences for users across all platforms and mediums.