Optical Illusions

Optical illusions (sometimes called also visual illusions) are images perceived in a manner that differs from objective reality. What the human eye sees is interpreted by the brain in a way that contradicts physical measurement of the source image.

You can find several types of optical illusions on this site:

cognitive illusions - whenever assumptions about the world lead to false perception (eg. ambiguous pictures, depth/motion/color perception or impossible objects)

afterimages - effects on the eyes or brain of excessive stimulation of brightness, tilt, color, movement, etc. (eg. grid illusions)

Optical Illusions (Ambiguity Pictures)

Ambiguous images are optical illusions which exploit similarities between two or more distinct images. They are also known as reversal images, puzzle images and perceptual rivalry.This is definitely one of the best-known optical illusions of all times! What do you see at first glance - an old woman or a young miss? They are both there!

Similar theme was used on a German postcard from 19th century.

A similar example of ambiguous visual illusions - father and son.

Whole family mind teaser - father with mother and daughter (by G. H. Fischer).

Sigmund Freud and what really on his mind is.

A landscape and the face of a bearded man.

Profile of Salvador Dali and a strange woman.

An old couple - see profiles of faces - is remembering the times when they were young and full of life - see the sitting characters ("Forever Always" by Octavio Ocampo©)

At first sight, what do you see? Do not focus on one region, now look again. You may be surprised (by Joseph Jastrow).

Rabbit and duck one more time.

Swan and squirrel ambiguous image (by G. H. Fischer).

This one is interesting. Children will probably see a group of playing dolphins. But adults see usually something else. It's called Message of Love from the Dolphins (by Sandro Del-Prete).

You probably recognize the face in this painting (it is St. George), but if you look at his hair, you'll see that he is fighting a fire-breathing dragon. It's called "St. George the Dragon Slayer"

(by Sandro Del-Prete).

Most of the people see a donkey first, but if you look closer you'll find a seal, with its flippers where the donkey's ears are!

Is that a polar bear or a seal on the optical illusion picture below?

Eye Illusions (Ambiguity Pictures)

See the face of a soldier and a man that is bending over on the below eye illusion.

Beautiful scene. But there is something more to it.

Who do you like more - women or saxophone players?

Are there really just flowers?

You may read across and upright.A-B-C or 12-13-14?

It is quite interesting that all numbers can be created by using only two numerals - 4 and 8.

Color Blindness Tests

1st Color Blindness Test - can you see a "12" on this plate?

2nd Color Blindness Test - there is a "26" on this plate.

3rd Color Blindness Test - can you trace a line from one "X" to the other?

4th Color Blindness Test - you should see 58 (upper left), 18 (upper right), E (lower left) and 17 (lower right).

Moving Objects Illusions

There is only illusory motion in the following static image due to color contrasts and shape position. (© Akiyoshi Kitaoka: Used with permission.)

Another static picture. (© Akiyoshi Kitaoka: Used with permission.)

Motion is just an eye illusion. (© Akiyoshi Kitaoka: Used with permission.)

There is nothing moving below. (© Akiyoshi Kitaoka: Used with permission.)

A wonderful moving bicycle illusion. (© Akiyoshi Kitaoka: Used with permission.)

A hilarious moving curtain illusion. (© Akiyoshi Kitaoka: Used with permission.)

Moving circles. (© Akiyoshi Kitaoka: Used with permission.)

Boats on the picture are not moving. It's just an eye illusion. (© Akiyoshi Kitaoka: Used with permission.)

Stare at the dot in the center of the circle and then move your head closer to it. Neat!

Impossible Objects Illusions

Our brain tries to do its best usually, however, there are instances when it fails to process correctly what the eye sees. The brain makes sense of shapes and symbols. It's trying to put them together like a jigsaw puzzle, formulating that which isn't there to that which is believable. 2D figure is subconscionsly interpreted as 3D object although such object can not exist.The Penrose Triangle, also known as the tribar is one of the most well-known Impossible Figures. Try to trace a line in the triangle and you would have to trace it three times around the triangle before coming back to where you started. (by Roger Penrose)

The Penrose stairs is a variation on the Penrose triangle. You could climb the stairs forever and never get any higher. That is only possible in two dimensions. This endless staicase can be found also in the paintings of M. C. Escher or also in the movie Inception by Christopher Nolan. (by Roger Penrose)

This impossible object (blivet) is called "Devil's Fork" or "Three-Pronged Poiuyt" or "Schuster's Conundrum" (by D. H. Schuster)

This is one of classic optical illusions - it is called dancing elephant. Try to count the number of his legs (by Roger Shepard).

Given the wood do you think you could make this

Another impossible figure.

Is the blue wall in the block or on the block? Is it the back wall or the side wall? You can flip back and forth between the two valid interpretations (so-called multistable perception). This ambiguous line drawing called Necker Cube was discoverd in 19th century.

A realistic photo or just another undecidable figure?

Is this a complete cube or just 3 sides of it?

Try to arrange dice like this.

Another interesting building.

This corner house is a bit tricky. Question: Is the corner concave or convex? Use your palm to cover the upper half of the picture and the corner will be bulged out. However, if you cover the

lower half, then it will seem as the inner corner. Amazing.

Word Illusions

If you can read the following picture, then you can shout ...

Can you read the below?

At first glance, what do you see? Could it be the word "liar" or is it something more. I would definitely give this one a second look!

This painting is called "Optical Illusion" - literally - you can read it (by John Langdon).

Victory or defeat? Both (by Veja Magazine).

Have you ever noticed a hidden arrow in the FedEx logo? It stands for speed and precision. Check the space between "E" and "x".

Try to say the color of the words, instead of actually reading them. You will find it surprisingly difficult. The right half of your brain is trying to say the colors, the left half is trying to say the word itself. This brain teaser is used by mountaineers to test if their concentration is ok. (by J. R. Stroop).

Scary Skull Illusions

Frightened? Of a lady in mirror? Scary, isn't it. It's called "All is Vanity" (by Charles Allan Gilbert).

Can you see the hidden skull (by Istvan Orosz).

These women didn't scare you, did they (by George A. Wotherspoon)?

Dr. Jekyll and Mr. Hide scary illusion.Step away from your computer screen. You should see the two faces swap over! Come closer to the screen again and they swap again. Spooky, isn't it. This hybrid image was created by Phillippe G. Schyns and Aude Oliva of the Univ. of Glasgow. It proves that we may not be

seeing what's actually there, all the time.

You probably see Albert Einstein on this picture. However, if you stand up and step 15 feet away, you will see Marilyn Monroe on the same picture.

Disappearing Dots Illusions

In the following Hermann grid illusion the gray spots appear at the intersection because of the inhibitory response which occurs as a result of the increased dark surround. Take a closer look -

do you see any grey spots where the black lines intersect? In fact, there is nothing.

Lilac Chase (also known as Pac-Man illusion) is another example of afterimage complementary color (green as opposite to lilac). Follow the movement of the rotating pink dot with your eyes and the dots will remain only one color, pink. But if you stare at the black + in the center, the moving dot will turn green. (by Jeremy L. Hinton)

If you stare at one yellow dot for a while, the other yellow dots disappear.

Picture Illusions

Life's too short for the wrong job - that's the name of this great billboard campaign.  

Poster Illusions (click to enlarge)

nice building (by David MacDonald)

waterfall (by MC Escher)

waterfalls 2 (by Rob Gonsalves)

scary animal head

Visions of Quixote (by Octavio Ocampo©)

drawing hands (by MC Escher)

earth and heaven

encounter (by MC Escher)

horses

toilet

Taylor Hall

hilarious balloons

Ambiguity Visual Illusions

Can you see both the frog and the horse on this visual illusion?

This one is so famous. Turn the picture upside down to see how men see women after 6 beers.

Can you find "the hidden tiger"? Not the obvious one that everyone sees. Look for words in stripes (by Donald Rust).

Fish eating sailboats.

A mysterious face found on Mars. This is a real photo of the surface of Mars taken by Viking 1 in 1976.

Afterimage Illusions

An afterimage or ghost image is an optical illusion that appears in one's vision after the exposure to the original image has ceased (eg. the bright glow after looking into strong light). This persistence of vision allows a rapid series of pictures to portray motion, which is the basis of animation and cinema. A few of famous afterimages include illusions of Jesus, Che Guevara, US flag or Italian flag. Stare at the four black dots in the center of the image for 30 - 60 seconds. Then quickly close your eyes and look at something bright (like a lamp or a window with sunlight coming through

it). You should see a white circle with an image inside it.

Stare at the image for at least 30 seconds and then look at something white to see Che Guevara afterimage.

Stare at the image for at least 30 seconds and then look at something white to see Italian flag afterimage.

Stare at the image for at least 30 seconds and then look at something white to see US flag afterimage.

Rubin's vase is a classic example of multistable perception. The brain makes figure-ground distinction between the vase in the center (which is usually recognized first) and the contour of 2

faces by sides. (by Edgar Rubin)

There should be 11 faces on this picture. Average people see 4-6, sensible 8-10. The best see all 11, schizophrenics and paranoids 12 and more. And you? (don't take this one too seriously, I have even heard that there are 13 faces)

Can you identify a face in this coffee beans pile? Take your time, it is there.

Line Illusions

In this café wall illusion the parallel straight horizontal lines appear to be bent. Important is that each "brick" is surrounded by the grey line, so a colour in between the dark and light colour of the "bricks".

Hering Illusions suggests that the horizontal lines are bent, however, the distortion is caused by the background that simulates perspective and thus false depth perception is created. (by Ewald Hering)

Which line is a continuation of the black one - the blue or the red line? If you guess that it's the blue line then you are wrong. Take a paper or a ruler to verify that. Human brain very poorly

interpretes the path of diagonals. (by Johann Christian Poggendorff)

The diagonal line bisecting the larger, left-hand parallelogram appears to be considerably longer than the diagonal line bisecting the smaller, right-hand parallelogram, however, both diagonals are actually the same length. (by Friedrich Sander)

Are the diagonal lines parallel? Of course, they are - angle of the short lines helps to create the impression that one end of the longer lines is nearer to us than the other end. (by Johann Karl Friedrich Zöllner)

Slanted lines in the following illusions produce a great effect. Both rectangles are parallel - you can take a ruler to check it out.

Do you see some squares or rectangles? Really, this is nothing more than a bunch of lines going in every which direction, but the way our mind interprets these lines are totally different!

A perfect circle.

Sides of a square placed inside a pattern of concentric circles seem curved although they are straight (by Walter Ehrenstein).

3 perfect squares.

A nice visual illusion using perfect squares. (© Akiyoshi Kitaoka: Used with permission.)

Perfect squares one more time. (© Akiyoshi Kitaoka: Used with permission.)

Other Visual Illusions

Even though the letters are jumbled in the following paragraph, most people have no trouble reading it!Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Same color illusion, also known as Adelson's checker shadow illusion (published by Edward H. Adelson) depicts something hard to believe. Square marked B looks considerably lighter than square B, due to the "shadow" being cast upon it. However, color on both squares is precisely the same shade of grey. If you don't believe, use any eyedropper tool or print/cut the squares to verify that both square A and square B are precisely the same.

All grey rectangles are of equal luminance, although the ones in the dark stripes appear brighter than the ones in the bright stripes. (by M. White)

When you first look at this, how many colors do you see? Some might say they see 3 or even 4 colors, but there are 2 - red and green! People usually think they see 2 shades of red, but there is only 1. Look closely and you will notice on one side that white boxes surround the red boxes, and on the other side, green boxes do! Due to the placement of these boxes you get the "illusion" of different colors. Since white is not considered to be a color (it is the presence of all colors in

scientific terms) we can safely say that there are 2 colors present here! Still don't understand?

The tabletops are identical in shape and size! I haven't believed that either, until I measured it myself.

The lower figure appears larger, however, both figures are identical. (by Joseph Jastrow)

The Ebbinghaus illusion or Titchener circles depicts relative size perception. Which central circle is bigger? The left one or the right one? Are you sure?

Both green lines have the same length. This Ponzo illusion uses the fact that human brain interpretes the image with perspective, however, it's just a simple 2D image.

Which soldier is taller? This is a variation of Ponzo illusion which suggests that the human mind judges an object's size based on its background.