The Secrets Behind 5 Optical Illusions

Magic Eye

Magic Eye images are perhaps some of the most well-known optical illusions, having spawned a pop culture craze when engineer Tom Baccei and 3D artist Cheri Smith debuted them in the 1990s. While they may first appear like nothing more than colorful static, each mosaic-like picture conceals a 3D image. 

The secret to seeing the hidden image lies in the repeating patterns. Each eye picks up slightly different parts of the pattern, so the key is for viewers to relax their eyes until they see double vision, by focusing on the image while attempting to look “through” it. This allows the brain to merge the different signals, creating the perception of a 3D image, not unlike how the brain gauges depth in the real world.

Magic Eye illusions are officially known as autostereograms — a fancy name for 3D images hidden within 2D graphics. To create a Magic Eye image, designers first choose a shape and render it in grayscale, with the lighter areas reading as closer and the darker areas reading as farther away. Next, they cover the initial shape with a colorful repetitive pattern. Specially designed computer software mixes the pattern with the gray shape, adjusting the pattern’s spacing to highlight how close or far away different parts of the shape are. When you look at it the right way, allowing your eyes to relax, your brain uses the pattern’s depth clues to reveal the hidden 3D image.

Checker Shadow Illusion

In the checker shadow illusion, two labeled squares among a gray-and-white checkered pattern appear to be wildly different shades of gray — only they’re not. There’s an explanation for this astounding phenomenon: While both squares emit the same light, the brain uses its past experience with shadows to determine that the square marked B, in the shadow of the checker, must be lighter than A — a square that is also, conveniently, surrounded by contrasting  lighter-colored squares. 

The checker shadow illusion was created by neuroscientist and vision science professor Edward H. Adelson in 1995. While human vision has been compared to a camera, the brain doesn’t actually measure light the same way a camera does. Instead, it guesses what we see based on what it’s learned from the past — a clever reminder that context, not just raw sensory data, plays a large part in what we see.

Rotating Snakes

Seeing motion where there is none is a rather disorienting visual trick, and  “rotating snakes,” one version of the peripheral drift illusion, perfectly exemplifies this. Created by Japanese psychologist Akiyoshi Kitaoka in 2003, the image itself is static, but a quick glance appears to cause the colorful circles to spontaneously spin in a slow, mesmerizing swirl. Yet if you pick and stare at just one single spot, the “motion” ceases. What gives? 

Research suggests that our visual systems are wired to detect motion even when there is none. When we look at repeating, asymmetric patterns such as the ones in the rotating snakes illusion, our brains interpret the shifting contrasts as cues for motion. This triggers the type of neural activity that typically occurs when we observe actual movement. Essentially, through contrast and light, it tricks our brains into thinking there’s motion by mimicking the neural signals associated with seeing something move. 

My Wife and My Mother-in-Law

The image known as “My Wife and Mother-in-Law” is a famous example of how our brains can interpret the same ambiguous image in multiple ways. At first glance, you may see an image of a hunched-up older woman with a large nose and a kerchief on her head — but on second glance, an elegant younger woman with a veil and chin angled away from the viewer emerges (or vice versa). There have been a few different versions of this popular illusion; though it first appeared on a German postcard in 1888, the most popular version was adapted by American cartoonist William Ely Hill for a humor magazine called Puck in 1915. 

Research has suggested that the image you see first, or most easily, may depend on your age. Younger participants in one study tended to see the “wife” (or younger woman) first, while older participants saw the “mother-in-law” (or older woman). It’s believed this can be chalked up to initial subconscious interpretation of an image according to one’s personal age-based biases. This serves as yet more proof that our perception of reality is strongly influenced by context.

Ames Room

At first glance, an Ames room looks like any ordinary rectangular space. Step inside one, though, and everything suddenly feels off. People standing in opposite corners appear comically different in size — one towering, the other tiny. Ames rooms are built with skewed walls, floors, and ceilings that create a trapezoidal shape; the unexpected size discrepancies are a trick of forced depth perception. 

Typically, an Ames room is viewed through a small peephole or from a specific viewing angle. This forces the brain to receive only one perspective on the scene, significantly reducing depth cues from the other eye. As a result, the distorted shape of the room is obscured, and the brain perceives the scene as if the objects inside are changing size.

The Ames room was first developed in 1946 by American ophthalmologist Adelbert Ames Jr. while exploring how experience affects perception. It’s since become an iconic fixture of amusement parks and even in pop culture — famous films such as 1971’s Willy Wonka & the Chocolate Factory and TheLord of the Rings trilogy have employed it to create deceptive visual dynamics, specifically to make certain characters appear much smaller than others.