Seven Rad Optical Illusions and Why They Fool Your Brain

Our eyes can’t be trusted and that’s not always a bad thing. Before motion pictures came about, Victorian kids would play with optical toys — little flip-books and wheels of still images that gave the impression of movement. In the late 1950’s “optical art” became all the rage, seemingly-swirling images dismissed as gimmicry by the artist were bought by the millions of early trippers. Now, anytime something appears as it shouldn’t, the image is analyzed on the internet like it’s a crime scene.

When you look at something, sight — your actual visual perception — only does half the job. To really know what you’re looking at, your brain fills in the gaps that your vision leaves with knowledge and expectations. Time on this Earth tells you that when you see a photo of someone holding up the Leaning Tower of Pisa with just their finger, they’re not really doing that. Your eyes go “Whoa! They’re holding up the Tower of Pisa with just a finger!” but your brain goes “Wait, wait, wait — we’ve seen this on Facebook before.”

But because perception is an “indirect, interpretive top-down process” and you don’t know what dynamic visuals the world is going to throw at you next, it’s way too easy to get tricked. But because being tricked is half of the fun, here are some of our favorite optical illusions:

1. Remorseful T. Rex

While this T. Rex seems to follow the viewer’s movement with longing eyes, it’s really a trick of perspective. As Phil Plait explains at Slate life experience has taught us to expect faces to stick out and knowing this, original designer/magician Jerry Andrus created a creature with a face that is actually concave. In a different view, you would see that the right eye is actually farther away from the viewer than the left eye; the way the face is bent tricks us to misinterpret the head as spinning. Making assumptions from bad clues creates the illusion — but does make for a good party gag. To download and make your own, go here.

2. The Checker-Shadow Illusion

Seeing in color is important — it’s assumed to be the biggest factor in the necessity of seeing the similarities and differences between objects. But sometimes we even interpret the accuracy of colors wrong.

The seemingly darker checker square that she is moving is the exact same color as the square she places it on. The illusion here has multiple factors at play but the main reason being the shadow cast on the board. Professor of Vision Science Edward Adelson explains on his blog that this shadow makes it that the seemingly white surface of the board reflects less light than a black surface in full light. Your brain is trying to compensate for the shadows, not realizing that:

“In the figure, the light check in shadow is surrounded by darker checks. Thus, even though the check in shadow is physically dark, it is light when compared to its neighbors. The dark checks outside the shadow, conversely, are surrounded by lighter checks, so they look dark by comparison.”

If you were to screen shot both squares, you would see that they are the exact same shade.

3. The False Pop Out

The way that this one works is that you’re supposed to choose the road you think is the odd-one out. But, as you watch, you’ll likely begin to think your guess was wrong — depending on the location of the first road. Designed by Rice University graduate student Kimberly Orsten and Professor James Pomerantz, the illusion is an example of a “false pop out.” If you watch the original video and pause at 0:02 it’s easy to see that the first road and the third road are the same. But with the long pause and then the sudden movement of the first road — going from homogenous to distracting — the viewer’s brain begins to doubt the pattern it first picked up on.

4. The Rotating Snakes

This type of illusion is probably the one you’re the most acquainted with — it’s the darling of ‘90s coffee-table books. It’s not complicated.

Academics call this one not “swirl ‘n twirl” but rather the “Rotating Snakes illusion”. In other words, it’s a peripheral drift illusion — an image that is interpreted as moving when it is actually still. This pattern is contrast modulated — when we see something with our peripheral vision our brain is processing it by pieces. Our brain tends to process high-contrast elements, like colors and shapes, faster than low-contrast ones. When the brain tries to interpret high-contrast and low-contrast factors at the same, the perception of motion occurs.

5. 3D Gifs

The cousin of normal GIFs, “3D GIFs” aren’t actually 3D at all. The white bars over the scene create an illusion of depth perception — the brain interprets them as the front of the scene, which is why this works particularly well with clips that include something moving from the background to the foreground. Again, because the lines create a mental division, this is another example of forced perspective.

It works, neuroscientist Stephen Macknik explains to Scientific American because the “3D system in humans is crap.” Our eyes work through a flat retina, which interprets objects as 2D, and then our brain relies on perspective clues so that we see things in 3D. If you’re getting the wrong clues, you’re going to see the wrong thing.

6. The Pigeon

When the smooth-gliding pigeon hits the lines, it seemingly begins to wobble with the head-bob of a real bird. However, the pigeon is actually moving just as elegantly as it was in the white section of the scene. This is called a kick-back illusion — the stripes are actually different widths and when the bird crosses over the different conditions, the apparent movement of the neck happens.

7. The Dress

With the New Year approaching, it’d be remiss to have a list without the most overwrought-viral sensation of 2015: The Dress.

By this time we all know, despite what your eyes might see, the dress is black and blue. But in a more turbulent time, when the internet raged through teams #goldandwhite and #blueandblack, psychologists and neuroscientist got to work to find out why so many people saw the image differently. What it really came down to was how different people see color in relation to light — it’s the backlighting that really throws people off. People who see the dress as white and gold did so because their internal model considered the dress to be light by the blue of the sky; those who saw blue and black saw it through a more “orange incandescent light.”. This difference in perception of natural life was, in part, divided by age — older people tended to see the bandage dress as white and gold. The fact that the image quality was so poor is the root of why there was ever a debate in the first place.

R.I.P. The Dress. May new optical illusions tear us apart in 2016.