Trippy eye tricks

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40 mind-boggling optical illusions that have stumped the internet

  • Optical illusions often go viral online.
  • Recent examples include an image with a hidden animal that appears if you shake your head back and forth and a hand-swapping trick.
  • Some illusions — like the infamous dress that appeared either blue and black or white and gold — have divided the internet.
  • INSIDER rounded up 40 confusing images, from classic optical illusions to baffling designs.
  • We've also included explanations for some of these illusions, which illustrate how our brains process and interpret color, peripheral vision, size, and more.

In the past few years, the internet has given us The Dress, a photo of a mysterious missing leg, and this disorienting floor design.

If you're still hungry for more, INSIDER rounded up a mix of classic optical illusions, baffling viral photos, and mind-boggling designs that'll leave your head spinning and illustrate how our brains process and interpret color, peripheral vision, size, and more.

One quick note: We've included explanations for many of the images, so scroll down slowly if you don't want to spoil the illusion.

The hidden animal is a cat — and you don't have to shake your head to see it.

hidden cat

As INSIDER's Gabbi Shaw previously wrote, if you zoom out on the original illusion, or look at a very small version of the image, the cat should become clear.

A video of this hand-swapping trick baffled the internet.

viral optical illusion

Chidera Kemakolam, who goes by kay_dera on Twitter, tweeted a brief clip of herself doing the trick in late August

In the video, Kemakolam starts by holding her left hand up to the camera, with her open palm facing the camera. After that, she wraps the fingers of her right hand around the palm of her left hand. Kemakolam then pushes both hands toward the camera, during which her right hand seemingly breaks free and appears, balled up into a fist, in front of her left hand in seconds.

The key to the trick is quickly making a fist with your front hand.

viral_optical_illusion 2
kay_dera/Twitter and Lucy Yang/INSIDER

Your hands never actually swap positions.

The amorphous shape at the bottom of this painting has confused people for centuries.

the ambassadors optical illusion
Wikimedia Commons (Public domain)

Titled "The Ambassadors," this painting was finished in by German artist Hans Holbein the Younger. It's currently on display at the National Museum in London, UK.

When you look at the painting head-on, you'll see what appears to be a large, deformed object at the bottom. But when viewed from a particular angle, the blob turns into a human skull before your eyes.

According to researcher Phillip Kent, this painting is one of the most famous examples of an anamorphosis — an irregularly shaped image that appears in its "true" form when viewed in an "unconventional" way — in art.

What color are the circles in this photo?

munker optical ilusion confetti

This colorful image went viral in mid-July after its creator, University of Texas professor, Dr. David Novick, shared it on Twitter.

Despite what you may see, it turns out all the circles are actually the same color. "The differences are subtle, though, and depend on the size of the image when it's viewed," Dr. Novick tweeted.

Dr. Novick's image, which he calls "Confetti," is an example of a classic optical illusion known as a Munker illusion. According to Danish professor Michael Bach, the Munker illusion reveals how much our perception of color is influenced by other surrounding colors.

At first glance, this photo seems to depict a man leaning over and embracing a woman who is sitting at her desk.

heels optical illusion whos legs are these

In May , a Twitter user named CJ Fentroy posted a picture of what appears to be two coworkers laughing and hugging. It also looks like the guy in the photo is rocking a light blue shirt, white skinny jeans, and black heels while the woman is wearing a plaid shirt in shades of magenta.

It's a cute but otherwise uneventful photo that you might just scroll past online if it weren't for Fentroy's caption. "At first, I thought he was wearing the heels," the Twitter user wrote.

If you look at the photo again, you'll start to question whose legs you're actually seeing.

Can you figure out who's wearing heels in this viral optical illusion
Boom_likean/Twitter and Lucy Yang/INSIDER

Upon closer inspection, it's hard to tell whether the guy in the photo is leaning over, with his head positioned above the girl's, or whether the girl is leaning over, with her head perched on the guy's left shoulder.

But the general consensus online seemed to be that the woman in the photo is the one wearing heels while the man is actually sitting down.

Depending on how you look at it, this illusion looks like Ben Stiller or Beyoncé.

ben stiller zoolander optical illusion hybird
Courtesy of Chris Frady

People were creeped out by this optical illusion after "The Late Late Show" host James Corden tweeted a photo of it in May

Originally created by Chris Frady (Reddit user Shikaca), this image first went viral in — and it was made by combining two photos of Zoolander and Beyoncé. 

At first glance, the illusion looks like a blurry photo of Ben Stiller's Zoolander character from his movie of the same name. But if you squint your eyes, Stiller's face seems to disappear; in its place, Beyoncé's face materializes. Her face also appears more clearly, compared to Stiller's face, when you look at a smaller version of the image or stare at it from a distance.


The Zoolander-Beyoncé photo is a variation of a simple optical illusion known as a "hybrid image."

albert einstein marilyn monroe hybrid image
Cmglee/Wikimedia Commons (Public domain)

One famous example of a hybrid image overlays the faces of Albert Einstein and Marilyn Monroe, as seen above. As Aude Olivia, the principal research scientist at MIT's Computer Science & Artificial Intelligence Lab, previously explained to Wired, this illusion is often used to study how our brains process visual stimuli and sight.

According to Olivia, who has created and used hybrid images in her research for decades, our eyes see "resolutions with both high spatial frequencies (sharp lines) and low ones (blurred shapes)." Up close, we focus on features with high frequencies, such as wrinkles or blemishes. But from a distance, sharp details become less visible and we instead register features with low frequencies, such as the shape of one's mouth or nose.

Hybrid images work by combining the high frequencies from one photo with the low frequencies from another. The result is a picture that can be perceived in two different ways, depending on the distance from which you look at it.


Optical illusions don’t “trick the eye” nor “fool the brain”, nor reveal that “our brain sucks”, … but are fascinating!

They also teach us about our visual perception, and its limitations. My selection emphazises beauty and interactive experiments; I also attempt explanations of the underlying visual mechanisms where possible.
Returning visitor? Check →here for History/News

»Optical illusion« sounds derogative, as if exposing a malfunction of the visual system. Rather, I view these phenomena as highlighting particular good adaptations of our visual system to its experience with standard viewing situations, confronted with an atypical situation. These experiences are based on normal visual conditions, and thus under unusual contexts can lead to inappropriate interpretations of a visual scene (=“Bayesian interpretation of perception”).

If you are not a vision scientist, you might find my explanations too highbrow. That is not on purpose, but vision research simply is not trivial, like any science. So, if an explanation seems gibberish, simply enjoy the phenomenon 😉.

More here: Bach & Poloschek () Optical Illusions Primer (PDF); on the programming: Bach (contact me for a PDF).

Thanking Inga who created new artwork () for the ‘eyes’. More from the Bach Family: Maren.

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12 optical illusions that show how colour can trick the eye

The Internet erupted in an energetic debate earlier this year about whether an ugly dress was blue and black or white and gold, with celebrities from Anna Kendrick (white) to Taylor Swift (black) weighing in. (For the record, I’m with Taylor – never a bad camp to be in.)

It sounds inane, but the dress question was actually tricky: Some declared themselves firmly in the blue and black camp, only to have the dress appear white and gold when they looked back a few hours later.

Wired had the best explanation of the science behind the dress’s shifting colours. When your brain tries to figure out what colour something is, it essentially subtracts the lighting and background colours around it, or as the neuroscientist interviewed by Wired says, tries to “discount the chromatic bias of the daylight axis.” This is why you can identify an apple as red whether you see it at noon or at dusk.

The dress is on some kind of perceptual boundary, with a pretty even mix of blue, red and green. (Frankly, it’s just a terrible, washed out photo.) So for those who see it as white, your eyes may be subtracting the wrong background and lighting.

Changing a colour’s appearance by changing the background or lighting is one of the most common techniques in optical illusions. As the examples below show, colours can change dramatically against different backgrounds. (If you’ve ever held a sock up to something black to see whether it was black or navy, you understand the concept.)

For example, in this classic shadow illusion by Edward H. Adelson, A and B are the exact same shade of grey:

Here's a minimalist illustration by Wikipedia user Dodek. The gray bar across the center is actually one constant colour:

In this image from BrainDen, the surface colours of A and B are the same. To test it out, just use your finger to cover the middle of the drawing, where the two squares meet.

In this illusion by Barton L. Anderson and Jonathan Winawer, the black and white chess pieces are the same colour:

If you want a dog of a different colour, just set it against a different background (via BrainDen):

There are actually only three colours in this image -- white, red and green (sorry, colour blind people). Also via BrainDen.

The blue and yellow border around this image by Jochen Burghardt creates the illusion that it is pale yellow, instead of white:

Contrasting colours can even give you the illusion of motion, as in this trippy graphic by Paul Nasca:

The same principle is at work in this motion illusion by Japanes professor Akiyoshi Kitaoka called "Rotating Snakes." As you stare at the image, the circles will appear to turn.

If you stare at the center of this illusion by Jeremy Hinton, you will eventually see a revolving green circle. When the lilac disappears, the adaptation of rods and cones in the retina leaves a green afterimage.

In Pinna's illusory intertwining effect, shown here in an illustration by Jochen Burghardt, colours give the illusion that circles are intertwining (they are actually concentric).

But probably the best illusion on the subject of the dress is by Randall Munroe of Xkcd, who immortalized the debate in an optical illusion cartoon form.

Washington Post

Eye - Optical illusion

Our Favorite Viral Optical Illusions Explained

What are ambiguous figures?

What image do you see? These last examples are probably some of the most well-known optical illusions. They go by different names, including bistable illusionsand ambiguous figures.

The word bistableis an electronics term that describes the condition of having “two stable states” in an electrical circuit. In optical illusions, one image evokes two mutually exclusive stable images within it. So above, the image can be perceived as a black vase on a white ground or two white faces on a black ground. The same configuration of lines and shapes can evoke two (or more) different entities, but not simultaneously. In our brains, only one entity can achieve perceptual dominance at a time.

These forms are also described as ambiguousfigures, where the figure is in an “uncertain” state in our brains, neither completely one entity, nor the other, nor both, but somehow, contradictorily, all three.

Yet another way to describe this illusion is as a Gestalt shift. In German, Gestalt means “shape,” so figures displaying this phenomenon are, essentially, “shape-shifters.” Or, rather, humans make shifts in their perceptions to see the different gestalts.

You&#;ve already seen another example of this illusion, the Impossible Trident with three and/or two prongs. Coming up are two more classic examples &#;


Tricks trippy eye

10 Cool Optical Illusions and How Each of Them Work

Optical illusions, more appropriately known as visual illusions, involve visual deception. Due to the arrangement of images, the effect of colors, the impact of the light source, or other variables, a wide range of misleading visual effects can be seen.

If you've ever struggled to see the hidden image in a single-image stereogram, you may have discovered that not everyone experiences visual illusions in the same way. For some illusions, some people simply are not able to see the effect.

Optical illusions can be fun and fascinating, but they can also tell us a great deal of information about how the brain and perceptual system function. There are countless optical illusions out there, but here is a sampling of some of the most fun and interesting.


The Hermann Grid Illusion

Sometimes we see things that aren't really there, and the Hermann Grid illusion is a great example of this. Notice how the dots at the center of each intersection seem to shift between white and gray? Like many optical illusions, different theories have been proposed to explain exactly why this happens.


The Spinning Dancer Illusion

The popular illusion made the rounds on blogs and websites a few years ago, supposedly as a test to determine if you are "left-brained or right-brained." In reality, the illusion occurs because our brains must attempt to construct space around the spinning figure.


The Ames Room Illusion

Would you be surprised to learn that the two people in the image at the left are actually the same size? Learn more about how this classic illusion works and how the effect has been put to use in special effects such as in the movie The Lord of the Rings.


The Ponzo Illusion

When you look off into the distance, objects seem closer together as they become further away. For example, the outside borders of a road or railroad appear to converge as they recede into the distance. The Ponzo illusion involves placing two lines over an illustration of a railroad track. Which line is longer? In reality, they are exactly the same length.


The Zollner Illusion

Sometimes the background of an image can interfere with how your brain interprets the image itself, as is the case with the Zollner illusion. This is one illusion that can actually make a viewer start to feel slightly queasy if you stare at it for too long!


The Kanizsa Triangle Illusion

According to the Gestalt law of closure, we tend to see objects that are close together as a related group. In the case of the Kanizsa Triangle, we even see contour lines that don't exist and ignore gaps in order to form a cohesive image.


The Muller-Lyer Illusion

Here's a classic illusion that still manages to stump a lot of people. Which line is longer? Actually, both lines are the same length. Surprised? Find out about how the Muller-Lyer Illusion works.


The Moon Illusion

If you've ever spent any time gazing up at the night sky, then you've probably noticed the moon illusion, in which the moon looks bigger on the horizon than it does higher up in the sky. Why does this happen?

Many theories have been proposed, although there is no universally agreed-upon explanation. You can read about how the moon illusion works and some of the possible theories that have been suggested.


The Lilac Chaser Illusion

In the lilac chaser illusion, the viewer observes several different visual effects over the span of about 30 seconds. First described in , the illusion is caused by a number of different factors including negative afterimages and what is known as Troxler fading. Check out the illusion yourself and learn more about how the lilac illusion works.


The Negative Photo Illusion

Here is another fun example of negative afterimages that produce a startling result. In the negative photo illusion, your brain and visual system essentially take a negative image and turn it into a full-color photo. Check out the illusion to give it a try and learn more about how it works.

trippy eye tricks

List of optical illusions

Name Example Notes Afterimage illusion Afterimagenpov.svgAn afterimage or ghost image is a visual illusion that refers to an image continuing to appear in one's vision after the exposure to the original image has ceased. Afterimage on empty shape (also known as color dove illusion) Afterimage.svgThis type of illusions is designed to exploit graphical similarities. Ambiguous imageDuck-Rabbit illusion.jpgThese are images that can form two separate pictures. For example, the image shown forms a rabbit and a duck. AmbigramAmbigram Real world Prank Fake animated (2).gifA calligraphic design that has several interpretations as written. Ames room illusion Ames room.svgAn Ames room is a distorted room that is used to create a visual illusion. Ames trapezoid window illusion Ames window.pngA window is formed in the shape of a trapezium. It is often hung and spun around to provide the illusion that the window rotates through less than degrees. Autokinetic effectThe autokinetic effect, or autokinesis, occurs when a stationary image appears to move. AutostereogramStereogram Tut Random Dot Shark.png
Stereogram Tut Eye Object Size.pngAn autostereogram is a single-image stereogram (SIS), designed to create the visual illusion of a three-dimensional (3D) scene from a two-dimensional image in the human brain. An ASCII stereogram is an image that is formed using characters on a keyboard. Magic Eye is an autostereogram book series. Barberpole illusionBarberpole illusion animated.gifThe barber pole illusion is a visual illusion that reveals biases in the processing of visual motion in the human brain. Benham's topBenham's Disc.svgWhen a disk that has lines or colours on it is spun, it can form arcs of colour appear. Beta movementPhi phenomenom no watermark.gifMovement that appears to occur when fixed pictures turn on and off. Bezold EffectBezold Effect.svgAn apparent change of tone of a colour due to the alteration of the colour of the background. BlivetPoiuyt.svgAlso known as "poiuyt" or "devil's fork", this illusion is an impossible image because in reality the shape cannot exist. Café wall illusionCafé wall.svgThis illusion is a pattern where different coloured squares on a wall appear to form horizontal curved lines. It is named such because this is the type of artwork often seen on café walls. Catoptric cistulaCatoptric theatre.jpgA catoptric cistula is a box with insides made of mirrors so as to distort images of objects put into the box. Checker shadow illusionChecker shadow illusion.svg
Grey square optical illusion proof2.svgThe checker shadow illusion shows that when a shadow is cast onto a checked board, the colours of squares A and B in the photos appear to be different, when in fact they are the same. Chubb illusionChubbillusion.gifThe Chubb illusion is an optical illusion or error in visual perception in which the apparent contrast of an object varies substantially to most viewers depending on its relative contrast to the field on which it is displayed. Color constancyHot air balloon - color constancy.jpgColour constancy is an example of subjective constancy and a feature of the human color perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions. A green apple for instance looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red. Color phi phenomenonThe color phi phenomenon is a perceptual illusion in which a disembodied perception of motion is produced by a succession of still images. Contingent perceptual aftereffectConvergence micropsiaCornsweet illusionCornsweet illusion.svgAn illusion where two colours can obviously be seen to be different when placed directly beside each other; however, when the two colours are separated by a thick black line, they appear to be of the same hue. Delboeuf illusionDelboeuf.svgAn optical illusion of relative size perception. The two black circles are exactly the same size; however, the one on the left seems larger. Disappearing ModelA trompe-l'œil body painting by Joanne Gair. Ebbinghaus illusionMond-vergleich.svgThe Ebbinghaus illusion, or Titchener circles, is an optical illusion of relative size perception. The two orange circles are exactly the same size; however, the one on the right appears larger. Ehrenstein illusionEhrenstein.svg
Ehrenstein Illusion.svgThe Ehrenstein illusion is an optical illusion studied by the German psychologist Walter Ehrenstein in which the sides of a square placed inside a pattern of concentric circles take an apparent curved shape. Fechner colorFigure-ground (perception)Cup or faces paradox.svgFilling-inTroxler fading.svgFlash lag illusionForced perspectiveEurope Disk 1 jpgApplication used in film and architecture to create the illusion of larger, more distant objects. Fraser spiral illusionFraser spiral.svgThe Fraser spiral illusion, or false spiral, or the twisted cord illusion, was first described by the British psychologist Sir James Fraser in The overlapping black arc segments appear to form a spiral; however, the arcs are a series of concentric circles. Gravity hillGrid illusionHermannGrid.svg
Grid illusion.svgAny kind of grid that deceives a person's vision. The two most common types of grid illusions are the Hermann grid illusion () and the scintillating grid illusion (). The first is characterized by "ghostlike" grey blobs perceived at the intersections of a white (or light-colored) grid on a black background. The grey blobs disappear when looking directly at an intersection. The second is constructed by superimposing white discs on the intersections of orthogonal gray bars on a black background. Dark dots seem to appear and disappear rapidly at random intersections, hence the label "scintillating". When a person keeps their eyes directly on a single intersection, the dark dot does not appear. The dark dots disappear if one is too close to or too far from the image. Hering illusionHering illusion.svgThe Hering illusion (): When two straight and parallel lines are presented in front of radial background (like the spokes of a bicycle), the lines appear as if they were bowed outwards. Hollow-Face illusionBjorn Borg Hollow Face.jpgThe Hollow-Face illusion is an optical illusion in which the perception of a concave mask of a face appears as a normal convex face. Hybrid imageHybrid image decomposition.jpgA Hybrid image is an optical illusion developed at MIT in which an image can be interpreted in one of two different ways depending on viewing distance. Illusory contoursKanizsa triangle.svgIllusory contours or subjective contours are a form of visual illusion where contours are perceived without a luminance or color change across the contour. Impossible objectImpossible cube illusion angle.svgIrradiation illusionIsometric illusionCubes at Heureka, optical illusion.jpgAn isometric illusion (also called an ambiguous figure or inside/outside illusion) is a type of optical illusion, specifically one due to multistable perception. Jastrow illusionJastrow illusion.svgThe Jastrow illusion is an optical illusion discovered by the American psychologist Joseph Jastrow in Kanizsa triangleKanizsa triangle.svgThe Kanizsa triangle is an optical illusion first described by the Italian psychologist Gaetano Kanizsa in It is a triangle formed of illusory contours. Kinetic Depth EffectThe Kinetic depth effect refers to the phenomenon whereby the three-dimensional structural form of a silhouette can be perceived when the object is moving. In the absence of other visual depth cues, this might be the only perception mechanism available to infer the object's shape. Additionally the direction of motion can reverse due to the existence of multiple 3D visual solutions. Leaning tower illusionThe Leaning tower illusion is an optical illusion that presents two identical images of the Leaning Tower of Pisa side by side. Lilac chaserLilac-Chaser.gifLilac chaser is a visual illusion, also known as the Pac-Man illusion. Liquid crystal shutter glassesLunar terminator illusionLunar terminator illusion is an optical illusion where the apparent source of sunlight illuminating the moon does not corresponding with the actual position of the sun. Mach bandsMach band.svgMach bands is an optical illusion named after the physicist Ernst Mach. McCollough effectGrid for McCollough effect.svgThe McCollough effect () is a phenomenon of human visual perception in which colorless gratings appear colored contingent on the orientation of the gratings. It is an aftereffect requiring a period of induction to produce it. Missing square puzzleMissing square puzzle.svg
Missing square edit.gifThe missing square puzzle is an optical illusion used in mathematics classes to help students reason about geometrical figures. Moon illusionMoon size illusion.pngThe Moon illusion is an optical illusion in which the Moon appears larger near the horizon than it does while higher up in the sky. Motion aftereffectMotion illusionAnomalous motion illusion1.svgMüller-Lyer illusionMüller-Lyer illusion.svgThe Müller-Lyer illusion is an optical illusion consisting of a stylized arrow. MultistabilityMusion EyelinerNecker cubeNecker cube.svgThe Necker cube is an optical illusion first published in by SwisscrystallographerLouis Albert Necker. Numerosity adaptation effectNumerosityadaptation.pngOrbison illusionOrbison illusion.svgThe Orbison illusion is an optical illusion that was first described by the psychologist William Orbison in Penrose stairsImpossible staircase.svgThe Penrose stairs was created by Lionel Penrose and his son Roger Penrose.[1] A variation on the Penrose triangle, it is a two-dimensional depiction of a staircase in which the stairs make four degree turns as they ascend or descend yet form a continuous loop, so that a person could climb them forever and never get any higher. Penrose trianglePenrose triangle.svgThe Penrose triangle was first created by the Swedish artist Oscar Reutersvärd in The mathematicianRoger Penrose independently devised and popularised it in the s, describing it as "impossibility in its purest form". Pepper's ghostPerceived visual angleVisualAngleAboveHorizonDefs.svgPeripheral drift illusionPDIFaubertHerbert.pngA motion illusion (/) generated by the presentation of a sawtooth luminance grating in the visual periphery. PhantogramPhantogram projection diagram.svgPhantograms, also known as Phantaglyphs, Op-Ups, free-standing anaglyphs, levitated images, and book anaglyphs, are a form of optical illusion. Phi phenomenonPoggendorff illusionPoggendorff illusion.svgThe Poggendorff illusion () involves the misperception of the position of one segment of a transverse line that has been interrupted by the contour of an intervening structure (here a rectangle). Ponzo illusionPonzo illusion.gifIn the Ponzo illusion () two identical lines across a pair of converging lines, similar to railway tracks, are drawn. The upper line looks longer because we interpret the converging sides according to linear perspective as parallel lines receding into the distance. In this context, we interpret the upper line as though it were farther away, so we see it as longer – a farther object would have to be longer than a nearer one for both to produce retinal images of the same size. Pulfrich effectThe Pulfrich effect is the effect that covering one eye with transparent but darkened glass can cause purely lateral motion to appear to have a depth component even though in reality it doesn't; even a completely flat scene such as one shown on a television screen can appear to exhibit some three-dimensional motion, but this is an illusion due to the fact that darkening the scene for one eye causes the photoreceptors in that eye to respond more slowly. Rubin vaseRubin2.jpgRubin vase (): an ambiguous or bi-stable (i.e., reversing) two-dimensional form. Sander illusionSander Illusion.svgIn Sander's parallelogram () the diagonal line bisecting the larger, left-hand parallelogram appears to be considerably longer than the diagonal line bisecting the smaller, right-hand parallelogram, but is in fact the same length. SilencingSilencinghue.jpgSilencing is an illusion in which a set of objects that change in luminance, hue, size, or shape appears to stop changing when it moves. Size–weight illusionThe size–weight illusion is also known as the Charpentier illusion or Charpentier–Koseleff illusion. Stepping feet illusionStepping-Feet-Motion-Illusion.gifThe stepping feet illusion is influenced by the contrast between moving objects and their background. Stroboscopic effectStrobe 2.gifSwept-plane displayTernus illusionThe Ternus illusion (/) is based upon apparent motion. ThaumatropeTaumatropio fiori e vaso, gifA thaumatrope is a toy that was popular in Victorian times. Trompe-l'œilTroxler's fadingTroxler's fading: When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Vertical–horizontal illusionVertical–horizontal illusion.pngThe Vertical-horizontal illusion is the tendency for observers to overestimate the length of a vertical line relative to a horizontal line of the same length. Visual tilt effectsTiltIllusion.jpg
TiltAfterEffect.jpgWagon-wheel effectWagonWheelEffect.gifWhite's illusionWhite illusion.svgWundt illusionWundt illusion.svgThe two red vertical lines are both straight, but they may look as if they are bowed inwards to some observers. The distortion is induced by the crooked lines on the background ZoetropeZoetrope.jpgZöllner illusionZollner illusion.svgThe Zöllner illusion is a classic optical illusion named after its discoverer, German astrophysicist Johann Karl Friedrich Zöllner.

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Trippy! Optical Illusions and How They Work

When you look at an optical illusion, something is obviously out of whack. Why won't your eyes cooperate? What's happening? Are your eyes playing tricks on you?

Many readers will remember the emergence of Magic Eye books in the early 's. Countless hours were spent staring at pages that seemed at first like senseless patterns. But the trippy materialization of 3-dimensional figures had people exclaiming aloud, and of course, drawing the attention of friends nearby, who could sometimes achieve the same experience. The optical illusions were a conversation piece for people who never would have had anything else in common, and paved the way for some cool products.

All Eyes on the Eyes

A visual illusion can be blamed on (or credited to, depending on your perspective) three causes. According to the American Academy of Ophthamology, you're tricked either because your two eyes aren't cooperating with one another (binocular vision), your brain is identifying one thing while your eyes are observing another (called the eye-brain connection), or because you think you're seeing something after it is gone (persistence of vision).

Binocular Vision

The first potential cause of an illusion is because your eyes usually work together as a seamless team, but they still have their own components, each seeing a different image. So when the brain combines the information from each eye, we get a complete picture. This includes depth perception, which is responsible for the Magic Eye illusions we mentioned earlier. It also explains how one eye can fill in missing information for the other if needed. When a designer creates an image that circumvents our eyes' teamwork, an illusion is the result.

Eye-Brain Connection

We all know that train tracks are parallel, and thus never converge. Why then, when we stand in the middle of a track and view the horizon, do we see the tracks coming closer to one another? This is an example of the eye-brain connection, where the eye simply reports a set of data to the brain, and the brain does the work of interpretation. Usually, the brain and eye are "on the same page", so to speak, and the brain concludes accurately. But occasionally, logic needs to trump our brain's visual explanation. Otherwise, we would never board a train again.

Persistence of Vision

For 1/30th of a second after you see something, the image lingers in your mind. A fraction of a second doesn't seem like a long time, but when a series of images flash before you, the impression from one blends to the other, creating the illusion of motion. Actually, this is where we get cartoons and motion pictures. The reality is that half of the time, the screen is truly dark. The other half of the time, images appear quickly, one after the other. As your brain fills in the gaps, using this lingering impression, or "persistence of vision", motion is detected, or rather, created. And if our brains are doing half of the work, then perhaps movie tickets should be half the price!

Of course, if in daily life you see spots on your vision or any blurring, make an appointment right away. This can be a sign of trouble, and your doctor can help.

Today, optical illusions are still used for the novelty experience, but they're also used for treatment of some eye disorders. Not to mention, these tricks bring the miraculous functions of the human eye to the attention of people who may not have considered how their eyes work.

For questions or comments, contact Woodhams Eye Clinic.


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