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					Optical Illusion

               Optical illusion
• An optical illusion is characterized by visually
  perceived images that differ from objective
    ALLAH in clouds (It’s no illusion, it’s reality)
• An image of clouds making Arabic word
Adelson's checker shadow illusion
• Squares A and B are the same color
• A rectangle of the same color has been drawn
  connecting the two squares
         Hermann grid illusion
• An example of the Hermann grid illusion. Dark
  blobs appear at the intersections
       Scintillating grid illusion
• Dark dots seem to appear and disappear at
The dots are all white, but appear to change color.
Stare at the fixed white dot and the scintillating will stop.
       1. Perceptual organization
• Reversible figure and vase

• (Cont…)
                 Rubin vase
• a famous set of cognitive optical illusions
  developed around 1915 by the Danish
  psychologist Edgar Rubin.
        Usage: The Division Bell
• The album cover artwork for Pink Floyd's The
  Division Bell is an example of a Rubin-vase-like
• The two metal heads in profile facing each
  other form the image of a third face looking
  directly at the viewer.
      1. Perceptual organization
• Duck-Rabbit illusion
           What can you see

• Can you see both the frog and the horse on
  this visual illusion?
                      Kanizsa triangle
• The Kanizsa triangle is an optical illusion
  first described by the Italian psychologist
  Gaetano Kanizsa in 1955.
• In the accompanying figure a white
  equilateral triangle is perceived, but in
  fact none is drawn.
• This effect is known as a subjective or
  illusory contour.
• Also, the nonexistent white triangle
  appears to be brighter than the
  surrounding area, but in fact it has the
  same brightness as the background.
         2. Depth and motion perception
• In the Ponzo illusion the converging parallel lines tell the brain that the
  image higher in the visual field is farther away therefore the brain
  perceives the image to be larger
• In fact, the two images hitting the retina are the same size
              Ponzo Optical Illusion
• The threered lines
  are duplicates, they
  are the exact same
    3. Color and brightness constancies

•   Gradient-optical-illusion

•   The contrast of the object will
    appear darker against a black field
    which reflects less light compared
    to a white field even though the
    object itself did not change in

•   The horizontal grey bar is the
    same shade throughout.
                       Optical Illusion
• the colored regions
  appear rather different,
  roughly orange and
  brown. In fact they are
  the same colour, and in
  identical immediate
  surrounds, but the brain
  changes its assumption
  about colour due to the
  global interpretation of
  the surrounding image.
• Also, the white tiles that
  are shadowed are the
  same color as the grey
  tiles outside of the
• An optical illusion.
  The two circles seem
  to move when the
  viewer's head is
  moving forwards and
  backwards while
  looking at the black
• Floor tiles at the Basilica of St. John Lateran in
  Rome. The pattern creates an illusion of three-
  dimensional boxes.
The Spinning Dancer
              The Spinning Dancer
• Some observers initially see the figure as spinning clockwise and
  some counterclockwise.
• The illusion derives from the lack of visual cues for depth. For
  instance, her arms could be swinging either in front of her to the
  left or behind her to the left, and hence with her circling clockwise
  or counter-clockwise on either her left or right foot.
• She changes leg because she is facing either towards or away from
  the observer, there being no surface features on the silhouette to
  indicate at any point which side of her is presented: the least
  ambiguous positions are her profiles when she is on either side of
  her circle, though it's still not known whether the foreground or
  background leg is on the floor, and from where she moves
  indeterminately either on the near or far arc across to the other
      afterimage or ghost image

• One of the most common afterimages
  is the bright glow that seems to float
  before one's eyes after looking into a
  light source for a few seconds
• If the viewer stares at this image for
  20-60 seconds and stares at a white
  object a negative afterimage will
  appear (in this case being cyan on
  magenta). This can also be achieved by
  the viewer closing his/her eyes and
  tilting their head up.
           Barberpole illusion

• Reveals biases in the processing
  of visual motion in the human
• When a diagonally-striped pole is
  rotated (horizontally) around its
  vertical axis, it appears as though
  the stripes are moving in the
  direction of its vertical axis
                    Benham's top

• When the disk is
  spun, arcs of pale
  color — called
  Fechner colors or
  pattern induced
  flicker colors (PIFCs)
  — are visible at
  different places on
  the disk.
• Not everyone sees
  the same colors.
• The phenomenon is
  not entirely
              Bezold effect
• The red seems lighter combined with the
  white, and darker combined with the black.
       Blivet (Impossible trident illusion)
• An impossible object
• It appears to have three cylindrical prongs at
  one end which then mysteriously transform
  into two rectangular prongs at the other end.
• his blivet portrays two irreconcilable
  perspectives at once, creating a "lost" layer
  between the top two rods, and an impossible
  extra, vanishing rod in between the bottom
 Impossible object illusion
• "A variation on the
  2 or 3 prong
  image, inspired by
  the work of Walter
  Wick, who
  managed to
  photograph his
  version using a
  partially reflective
  piece of glass and
  very careful
  lighting to create
  the illusion. "
•   Andreas Aronsson is a professional IT technician by day and an awesome optical
    illusion artist at night:
•   He made this cleverly drawn "impossible figure" that at a glance look perfectly
    fine, but upon closer inspection will give your mind some sort of a Twilight Zone
                    Café wall illusion
• first described by Richard
  Gregory in 1973

• This optical illusion
  makes the parallel
  straight horizontal lines
  appear to be bent.

• It is essential for the
  illusion that each "brick"
  is surrounded by a layer
  of "mortar" (the grey in
  the image). This should
  ideally be of a color in
  between the dark and
  light color of the "bricks".
Architecture inspired by the café wall illusion, at
Melbourne Docklands
              Necker Cube
• The Necker Cube is an ambiguous line drawing
• impossible cube on the right
What shape is this exactly
                Contrast effect
• Successive contrast occurs when
  the perception of currently viewed
  stimuli is modulated by previously
  viewed stimuli.
• when one stares at the dot in the
  centre of one of the two colored
  disks on the top row for a few
  seconds and then looks at the dot
  in the centre of the disk on the
  same side in the bottom row, the
  two lower disks, though identically
  colored, appear to have different
  colours for a few moments.
            Delboeuf illusion
• The two black circles are exactly the same size;
  however, the one on the left seems larger
          Ebbinghaus illusion
• The two orange circles are exactly the same
  size; however, the one on the left seems
           Ehrenstein illusion
• the sides of a square placed inside a pattern of
  concentric circles take an apparent curved
             Fraser spiral illusion
• The Fraser spiral illusion was
  described by the British
  psychologist James Fraser in 1908.
• The illusion is also known as the
  false spiral, or the twisted cord
• The overlapping black arc segments
  appear to form a spiral; however, in
  fact, the arcs are a series of
  concentric circles
                  Hering illusion
• The Hering illusion is an optical
  illusion discovered by the
  German physiologist Ewald
  Hering in 1861
• The two vertical lines are both
  straight, but they look as if they
  were bowing outwards
• The distortion is produced by
  the lined pattern on the
  background, that simulates a
  perspective design, and creates
  a false impression of depth
             Jastrow illusion
• the two figures are identical, although the
  lower one appears to be larger.
   Lilac chase/ Phi phenomenon
• Described by Max Wertheimer in his 1912
  Experimental Studies on the Seeing of Motion
• In the phi phenomenon, a succession of still
  images with an omission gives the illusion of
  movement. The phi phenomenon always takes
  the background color.
• In this Lilac chaser illusion, the omitted space
  appears to be filled with a green circle when
  viewed long enough
                  Phi phenomenon

Keep concentrating on the black + in the center of the picture. After a short
period, all the pink dots will slowly disappear and you will only see a single
green dot moving in a circle.
         Missing square puzzle
• Optical illusion used in mathematics classes to
  help students reason about geometrical

• It depicts two arrangements of shapes, each
  of which apparently forms a 13×5 right-angled
  triangle, but one of which has a 1×1 hole in it.
• The key to the puzzle is the fact that neither of the 13×5 triangles has the
  same total area as its supposed component parts.

• The four figures (the yellow, red, blue and green shapes) total 32 units of
  area, but the triangles are 13 wide and 5 tall, so it seems, that the area
  should be S=13x5/2=32.5 units. But the blue triangle has a ratio of 5:2
  (=2.500:1), while the red triangle has the ratio 8:3 (≈2.667:1), and these
  are not the same ratio. So the apparent combined hypotenuse in each
  figure is actually bent.

• The amount of bending is around 1/28th of a unit, which is difficult to see
  on the diagram of this puzzle. Note the grid point where the red and blue
  hypotenuses meet, and compare it to the same point on the other figure;
  the edge is slightly over or under the mark. Overlaying the hypotenuses
  from both figures results in a very thin parallelogram with the area of
  exactly one grid square, the same area "missing" from the second figure.
• The integer dimensions of the parts of the puzzle (2, 3, 5, 8, 13) are
  successive Fibonacci numbers
Missing Square Illusion (Variation)
               Moon Illusion
• The Moon illusion is an optical illusion in
  which the Moon appears larger near the
  horizon than it does while higher up in the sky.
• This optical illusion also occurs with the sun
  and star constellations.
• It has been known since ancient times, and
  recorded by numerous different cultures.The
  explanation of this illusion is still debated
Moon Illusion 2 Main Theories

1. The Ponzo Illusion
   – Two yellow bars are drawn across railway tracks which converge towards
     the distant horizon.
   – To the eye, the top bar appears to be wider than the bottom bar.
   –   In the same way, with a low-lying moon the trees and houses, which are familiar
       foreground reference points, appear smaller against the moon, which appears
       bigger than it really is.
   –   Sceptics of this theory point to airline pilots who also see the illusion, although
       they have no ground reference points

2. Alternate View
   –   the brain perceives the sky as a flattened dome rather than the true
       hemisphere it really is. (Explained in next slide)
solstice moon

•   The full Moon beams through trees in Manchester, Maryland. Credit: June 16 ,
    2008 Edmund E. Kasaitis. Copyright 2008; all rights reserved.

•   Maybe it's the shape of the sky. Humans perceive the sky as a flattened dome,
    with the zenith nearby and the horizon far away. It makes sense; birds flying
    overhead are closer than birds on the horizon. When the moon is near the
    horizon, your brain, trained by watching birds (and clouds and airplanes),
    miscalculates the Moon's true distance and size.
Taller Than The Eiffel Tower
Illusion with Moon
              Sander illusion
• 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.
     Vertical–horizontal illusion
• It is the tendency for observers to
  overestimate the length of a vertical line
  relative to a horizontal line of the same length
              Zöllner illusion
• In this figure the black lines seem to be
  unparallel, but in reality they are parallel. The
  shorter lines are on an angle to the longer
  lines. This angle helps to create the impression
  that one end of the longer lines is nearer to us
  than the other end
                Müller-Lyer illusion
• an optical illusion consisting of nothing more than an arrow. When viewers
  are asked to place a mark on the figure at the mid-point, they invariably
  place it more towards the "tail" end
• The set on the bottom shows that all the arrows are of the same length.
Muller-Lyer Ticket Window
              The Orbison illusion
• The Orbison illusion is an optical illusion that was first
  described by the psychologist William Orbison in 1939.
• The bounding rectangle and inner square both appear
  distorted in the presence of the radiating lines.
• The background gives us the impression there is some sort of
  perspective. As a result, our brain sees the shape distorted.
            Poggendorff illusion
• involves the brain's perception of
  the interaction between diagonal
  lines and horizontal and vertical
• a straight black and red line is
  obscured by a grey rectangle. The
  blue line, rather than the red line,
  appears to be a continuation of
  the black one, which is clearly
  shown not to be the case on the
  second picture
     Peripheral drift illusion (PDI)
• This illusion was first described by Faubert and Herbert
  (1999), although a similar effect called the "escalator
  illusion" was reported by Fraser and Wilcox (1979). A
  variant of the PDI was created by Kitaoka and Ashida
• The illusion is easily seen when fixating off to the side,
  and then blinking as fast as possible. Most observers
  see the illusion easily when reading text (such as this
  article) with the illusion figure in the periphery. Motion
  is consistently perceived in a dark-to-light direction, so
  the two circles to the right should spin in opposite
                 Illusion Images
• Do you find something
  unusual in this picture?
  Can you see any human
  face in this optical
  illusion? If not just
  move away from the
  screen and try focusing
  on the center portion.
         Dice Optical Illusion
• impossible
Good and Evil
               Flowing Leaves
• The brown leaf shapes against a green background
  make this look as if the entire group is flowing—
  making waves if you focus on the picture as a whole.
           Painting Or Reality
• Do you see people trying to climb out? It is
  actually a presentation of a floor painting.
        Wheels Optical Illusion
• Which wheel is moving faster? or are they
  even moving?
A wonderful moving bicycle illusion
          Stare Optical Illusion
• Just stare at it and watch some cool things
• This illusion looks curved around all the sides
  of the square, but its not.
• This optical illusion looks like one of those
  hologram cups you get at a fast food drive
                       Rainbow Ghost
• In 2007, John Shadowsky introduced invented it. It gave us ability to see
  black and white photos in full color! This is the closest you get to having
  super-hero powers. It was really an extraordinary value added to the
  optical illusions field, but also an interesting phenomena brought to
  attention of those studying visual sciences.

• To see this optical illusion in it’s full capacity, wait for the animated .gif to
  loop to its start. You’ll know you’re there when you see a full colored
  rainbow appear. Now stare at the center dot for few seconds, and at one
  time the animation will switch. But don’t move your eyes from central dot
  just yet! What do you see? If you followed my procedure precisely, sooner
  or later you’ll find out that the animation below consists of two similar
  images. Only difference between them, is that one is in color, and the
  other is black and white. After staring at the color rainbow’s central dot,
  negative colors burnt in your retina, and you were able to see the black
  and white photo in full color!
Rainbow Ghost (cont)
Rotation direction
 In which direction does it spin?
Panting (impossible)
Hypnotic Spinning Spiral Optical Illusion
            Vanishing illusion
• When observers
  approach the image
  keeping their eyes
  on the center of the
  image, fireflies of
  blue light appear to
  escape. Then, some
  or all of them
  appear to extinguish
  (Troxler effect).
Ouchi illusion

 The inset appears to move.
Never ending stairs (imaginary)
 The Hidden Tiger Optical Illusion
• It was created by
  American wildlife artist
  Rusty Rust, and it shows
  a huge Bengal Tiger
  standing in a bamboo
• Your mission now is to
  look for “The Hidden
  Tiger” in the image
• Where is the hidden
   The Hidden Tiger Optical Illusion
• The hidden tiger can be found in the tiger's
  stripes. Read his stripes - they spell - "THE
   Hidden Horse in Water Illusion
• Find the hidden
  horse, How many
  horse do you find in
  this picture.
• The two pink diagonal lines - Are they the
  same shade of pink or of different shades?

• Look carefully,
they are the same.
Don't let your eyes
deceive you!
  Do you see the two shades of green

• Would you believe that there is actually only
  one shade of green?
             What do you see?

• At first glance, this image
  consists of black
  splotches, but look closer.
  It actually spells a word.
Stare at the black dot in the middle

• You should see the outer edges of the circle fade away!
          Read the following passage

•   Did you catch the two "The"s? Most people miss this obvious redundancy.
   Watch the lines move around the

• Do they appear to periodically change direction?
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.
How many F's does the following
      passage contain?
                     5 Fs
• Did you count all 6 of them or only 3?
• Most people forget to include the F's located
  in the word "of".
• Some people percieve f as v in rythem
                         rotating snakes
•   Zack Lynch posted this fabulous optical illusion called rotating snakes by A Kitaoka
              The glowing core
• Look into the centre
  (white point) and
  stare for a while. How
  many colours can you
  see altogether in the
• You should see a
  purplish circle... and
  the 4 rotating 'wings'
  are tinted green.
  Make sure you always
  keep focused on the
          Rotating dot whirlpool
• Wow! Try staring
  at this for more
  than 5 seconds
  without going
  crazy. Then try
  following it round
• Curves constantly
  die out and then
  re-evolve as part
  of another curve.
        Hidden Women Face Illusion
There is a Hidden Women Face in the image. find her ?

If you look on the shore of the treeline, you'll see her,
she's lying horizontally and the tops of the trees are her hair...
                   Dolphin Illusion
• What did you see in the picture?
  You saw a couple in an intimate
  pose, right?
• Interestingly, research has
  shown that innocent children
  cannot identify the intimate
  couple because they do not
  have prior memory associated
  with such a scenario.
• What they WILL see, however, is
  the nine dolphins in the picture!
• Our mind may indeed corrupted
  and need help to identify it.
• In the top illusion image, the
  balls appear to be resting on
  the pattern.
• In the bottom illusion image,
  there are three balls appear to
  be floating.
• But, if you look at them further
  detail, you will notice that they
  are not floating. Only the
  placement of the shadows is
Is it a tree or a river? or both?
                                What’s it?

•   it was just a piece of paper!
Its just a lamp on brown wall
Count horses!
              Bourdon illusion
• The upper side of the left-lower triangle is
  actually aligned with the upper side of the right-
  upper triangle, the former appears to tilt counter
  clockwise while the latter clockwise
          Beware of exponential deals
•   The king of Seedonia's son was saved by a young peasant girl happened by just in time and pulled
    the prince to safety. The grateful king invited her home to reward 1,000,000 seedo (money unit) for
    saving the prince.
•   The girl looked at the chess board and suggested an alternative reward:

•      “Put one Seedo on the first square of the chess board. Tomorrow, remove the Seedo from the
    first square and put two Seedos on the second square. The day after tomorrow, remove the two
    Seedos and put four Seedos on the third square. The next day, put eight Seedos on the fourth
    square, and so on each day. On the 64th day, I will leave with whatever amount is on last square of
    the board.”

•   He agreed to the girl’s wishes, thinking he would spend quite a bit less than his original offer.

•   The king went broke long before the 64th day. The girl took over the palace and declared herself
    Queen of Seedonia. She ended up with

    18,446,744,073,709,551,616 Seedos = (2 power 64) at 64th day

•   The moral of the story is: Beware of exponential deals.
                   dancing elephant
Try to count the number of his legs (by Roger Shepard).
• Is the blue wall in the block or on the block? Is
  it the back wall or the side wall?
  They look pretty normal, right?

• Now go to next slide
• Gross, right? Those are the same two photos (the one on the
  right is now on the left, but rightside up this time. The
  distortions to the one face, which didn't look so bad when it
  was upside down, now look... grotesque.
• In fact, we often don't even notice it, and the expression looks
  pretty close to the normal face in last image.
• While approaching , the
  radial lines appear to rotate
  in counter-clockwise
  direction, whereas when
  receding from it, they appear
  to rotate clockwise.
• This illusion has first been
  published in: Martinez-Conde, S.,
   Pérez, M. & Martinez, L. (2005). Flipar en
   Colores. Quo, July 2005, 110-115.
Imaginary stairs
           Black Hole Illusion
• You keep getting deeper and deeper into.
• When staring into the middle it appears as
  though the black hole is getting larger and
  larger, or that are falling into it.
Black Hole Illusion
Beautiful Lady In The Smoke Illusion

  The smoking cigar in an ashtray holds a lady’s figure
       Illusion CandlesStumble

Mirrored glass behind the candles gives the
 impression of infinite light.
    Female and Male Face Optical Illusion

•   Illusion by Richard Russell of Harvard University shows two faces which are perceived as male and female.
    Why does our brain perceived the image on the right is a male, and the image on the left as female?
    What’s the difference between the images?

•   The difference?
•   Both images are off the same androgynous face. The only difference is the image on the right has a higher
    contrast (male), whereas the image on the left has a lower contrast (female).
                       Camel Shadow Illusion

•   At first glance you see a herd of camels walking across the desert but in actuality the camels are the little things that look
    like rocks and the ones you first notice are the shadows.

• Human hands
Vinnie? Could be a towel.
Chinese fields look like colorful stained glass patterns

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Description: A collection of Optical Illusions / compiled by me from versatile resources