Easy Optical Illusions Crack in the Earth
The impossible trident was first published in 1964 by D.H. Schuster.
The impossible fork is exactly that: impossible. When looked at from the bottom, it appears to have three prongs, but at the top it clearly is only split in two.
The shape is impossible because it would violate rules of Euclidean geometry.
These dots appear to be moving because of a phenomenon called illusory motion.
Illusory motion is the appearance of movement in a static image. Here, the dots appear to wobble, but it's just a normal, non-moving pattern.
A study led by researchers from the Barrow Neurological Institute explained that tiny eye movements and blinking cause the dots to look like they're moving.
The two dots in the middle appear to be different sizes — but are actually the same.
The circle on the left appears to be larger than the circle on the right because it's surrounded by smaller circles.
This illusion happens because the brain uses context in order to judge size — like when the brain assumes something small is far away. Since the circle on the left is surrounded by smaller circles, it makes sense that the brain thinks it's larger than a circle surrounded by much larger circles.
This illusion is known as the "cafe wall illusion" since it was first observed outside a cafe.
Richard Gregory discovered this illusion at a cafe in the 1970s. The gray lines appear to be slanted, but if you cover up the black and white tiles, you'll see that the lines are actually straight. For this illusion to work properly, the tiles have to be offset by half a tile, and the gray lines have to be in place.
The effect works because of the way neurons interact in the brain. Your retinas dim and brighten different parts of the gray lines because of the way the tiles are positioned. When there's a brightness contrast between two tiles (like a black tile on top of a white tile), your neurons interpret these changes as small wedges — making the lines appear slanted.
Those black dots you're seeing in the grid aren't actually there.
This illusion dates back to the 1870s, when it was discovered by Ludimar Hermann.
The dots are the result of a neural process called lateral inhibition — the capacity of an excited neuron to reduce the activity of its neighbors. When a lot of light is let in to a retinal neuron (like the white bands), the neurons can't process all of it, so black dots appear.
This elephant is at the center of a "L'egs-istential Quandary."
Can you tell how many legs this elephant has? If looking at the legs is giving you a headache, you're not alone.
An easy to way solve this problem is to cover the feet. Then you'll be able to clearly see that the elephant only has four legs. The reason it looks so trippy is that the artist left the natural space for the feet blank, instead drawing the feet in the spaces between the legs. This confuses your brain and makes you see the spaces as legs as well.
The circle appears to be colored light blue — but it's actually the same shade of white.
This type of illusion first appeared in 1971, when psychologist Dario Varin published one in the book "Chromatic Contrast and Diffusion Phenomena."
The reason your eye perceives the circle to be the same color as the lines is relatively unknown.
The Jastrow illusion was seen in real life with these children's train tracks.
This illusion was discovered by Joseph Jastrow (who makes another appearance on this list) in 1889.
The two tracks appear to be different sizes when the shorter side of one track is directly next to the longer side of the other, but when one is placed on top of the other, it's clear that they're the same size. It's still not known why this error in perception occurs.
This illusion is called the Kanizsa triangle.
Calling this illusion, first seen in 1955, a triangle is actually a bit of a misnomer. There are no actual triangles anywhere in the illustration.
Your brain fills in the gaps in the line segments and the black circles, and assumes there should be a triangle there — also known as the phantom edge phenomenon.
These three lines appear to all be different lengths, but are actually the same size.
These lines look like they're all different lengths and a little bit offset, when in actuality they're all the same length and start and end on the same axis.
The orientation of the arrowheads is what confuses your brain. The line on which both arrows point outward looks shorter than the line directly below, whose arrowheads face inward.
A popular explanation for this illusion is the "carpentered world." People's eyes become accustomed to corners — so when we see angles like the arrowheads, our eyes perceive them as corners and completely overpowers the retinas, which say they're the same length.
"Rotating Snakes" is another example of illusory motion.
"Rotating Snakes" was invented by Akiyoshi Kitaoka in 2003. This specific type of illusory motion is called peripheral drift — while the one part that you focus on doesn't appear to move, all of the "snakes" in your peripheral vision appear to spin.
This is a drawing of both a duck and a rabbit.
While the original drawing was published anonymously, Joseph Jastrow first made a note of it in 1900.
This duck-rabbit hybrid is considered an ambiguous image. If you're having trouble seeing the rabbit, turn your head to the left: The duck's beak can also be the rabbit's ears.
Magic Eye posters were all the rage in the '90s.
Magic Eye came to America in 1993 in a book called "Magic Eye: A New Way of Looking at the World." Magic Eye illusions are officially known as stereograms, or 3D illusions. Technically, they're 3D illustrations hidden within 2D graphics.
Not everyone can find the hidden picture in a Magic Eye graphic — and if you can't, it could mean you have problems with your eyesight.
If you're really stumped, try getting really close to the illusion and focusing on one point. Slowly move backwards from the screen, and keep focusing on the one point.
Depending on your focus, you can see either a vase or two faces staring at each other.
This is a variation on the Rubin vase. The illusion was originally developed in 1915 by Danish psychologist Edgar Rubin.
If you focus on the black sections, you'll see two faces looking at each other. If you focus on the white space between, you'll see a vase.
This drawing is titled "My Wife and My Mother-in-Law." Can you see them both?
While both the artist's wife and mother-in-law are visible in this drawing, our eyes can only perceive one at a time.
This illusion, known as the Boring Figure, gets its name from Edwin Boring, who wrote a paper about the drawing in 1930.
This composite of Marilyn Monroe and Albert Einstein is known as a hybrid image.
This illusion can do more than just give you a headache. It can also help diagnose vision problems.
For example, if you wear glasses, try taking them off and leaning away fom the screen. Einstein might fade away altogether, and you'll only see Monroe.
This is because when someone has poor eyesight they lose their ability to see fine details and instead concentrate on the big picture. Einstein's more detailed features are laid on top of a blurry photo of Monroe — so someone with vision problems will focus on the blurrier face of Monroe.
"Waterfall" is a lithograph drawn by M.C. Escher. The waterfall's top and bottom appear to be at the same level.
The perpetually flowing waterfall is based on another classic optical illusion called an impossible triangle, or the Penrose triangle.
What makes this impossible? The water falls from the top, and is caught at the bottom. It then appears to flow from the bottom (clearly at a lower level) back to the top, which suddenly appears to be at the same height as the bottom.
This cube plays with human perception.
Another illusion created by M.C. Escher, the impossible cube first appeared in one of his lithographs called "Belevedere."
The cube is another example of a shape violating Euclidean geometry. Focus on the bottom of the cube: All the sides of the cube appear to be overlapping each other.
This is Troxler's fading circle. If you stare the dot for at least 20 seconds, the circle will completely fade away.
The circle fades away because of the eye's tendency to prioritize. If you focus on the dot, all other stimuli in your peripheral vision will fade away.
Your entire body adapts to stimuli like this. You can test this on your arm very simply: Put a small piece of paper on your arm, and, after a few seconds, if you don't move, you'll stop feeling the paper. Neurons adapt to new things and then move on. So, your eye sees the circle, but is more focused on the dot and unconsciously decides to stop seeing the circle.
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Source: https://www.insider.com/classic-optical-illusions-2018-1
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