Miscellaneous optical illusion

This page discusses Pinna illusion, Leaning tower illusion and Impossible World illusion.

Pinna illusion

Pinna illusion is the first visual illusion showing a rotating motion effect. In Figure below, the squares, delineated by two white and two black edges each, are grouped by proximity in two concentric rings. All the squares have the same width, length, and orientation in relation to the center of their circular arrangements. The two rings differ only in the relative position of their narrow black and white edges forming the vertexes. More precisely, the two rings show reversal of the vertex orientation and, consequently, opposite inclination of the virtual or implicit diagonal orientation polarity obtained by joining the two vertexes where black and white lines meet (Pinna, 1990; Pinna & Brelstaff, 2000).
When the observer’s head is slowly moved towards the figure with the gaze fixed in the center, the inner ring of the squares appears to rotate counter-clockwise and the outer ring clockwise. The direction of rotation is reversed when the observer moves away from the figure, the same squares of the inner ring appear to rotate clockwise, while those of the outer ring rotate counter-clockwise. The apparent motion is perceived instantaneously and in a direction perpendicular to the true motion. The speed of the resultant illusory motion appears to be proportional to that of the motion imparted by the observer. Figure 2 simulates the action of moving towards and away from the figure by physically expanding and contracting the pattern shown in Figure 1. The two concentric rings of squares now appear to counter-rotate when the gaze is fixed on the center and the observer is stationary. When the same figure is physically rotated clockwise, the inner ring appears to contract and the outer one appears to expand (Figure 3). The opposite effects are perceived when the figure is rotated counter-clockwise. (scholarpedia)

Pinna illusion (Classic Pinna illusion)

The Pinna illusion is comprised of two concentric circles of micropatterns. The two circles seem to counter-rotate when the viewer's head is moving forwards and backwards while looking at the black dot.

Additional images of Pinna illusion:
http://hompi.sogang.ac.kr/mkyang/O/visual/pinna.html alternate www.archimedes-lab.org/ alternate

Pinna's Intertwining illusion

Pinna's Spiral Intertwining illusion

Illusory intertwining and spiral effect
Consequences of the illusory convergence and divergence (loss of parallelism) are manifest in the two effects illustrated in Figure 12a-b, where the concentric circles, made up of squares, appear (a) intertwined when the implicit diagonals are alternated among the circles or (b) like a spiral when all the implicit polarities have the same orientation. The two effects rotate in opposite (clockwise vs. counter-clockwise) directions when the orientation polarities are explicit as illustrated in Figure 12c-d (Pinna & Gregory, 2002).

Leaning tower illusion

The leaning tower illusion is a visual illusion seen in a pair of identical images of the Leaning Tower of Pisa photographed from below. Although the images are duplicates, one has the impression that the tower on the right leans more, as if photographed from a different angle. The illusion was discovered by Frederick Kingdom, Ali Yoonessi and Elena Gheorghiu at McGill University, and won first prize in the Best Visual Illusion of the Year Contest 2007.

Leaning tower illusion: Tower of Pisa

The Leaning Tower Illusion is an optical illusion that presents two identical images of the Leaning Tower of Pisa side by side. Although the images are identical, we have the impression that the tower on the right leans more, as if photographed from a different angle.

Leaning tower illusion: Big Ben

This wonderful illusion was created by Frederick Kingdom and colleagues at McGill University. Big Ben appears to tilt more in the photo on the right, but in reality the two photographs are identical.

The illusion reveals the way in which the human visual system uses perspective to help construct our perception of 3-D objects. We say “construct” because the visual system has no direct access to 3-D information about the world. Our perception of depth results from neural calculations based on a set of rules. These rules include the following:
perspective (parallel lines appear to converge in the distance);
stereopsis (our left and right eyes receive horizontally displaced images of the same object, resulting in the perception of depth);
occlusion (objects near us occlude objects farther away);
chiaroscuro (the contrast of an object as a function of the position of the light source); and
sfumato (the feeling of depth that one gets from the interplay of in- and out-of-focus elements in an image, as well as from the level of transparency of the atmosphere itself).
Because the towers pictured in these paired images do not converge as they recede, the brain mistakenly perceives them as nonparallel and diverging.
(169 BEST ILLUSIONS, Scientific American SPECIAL ISSUE, July 12, 2010, page 8)

Identical images of tram lines

The leaning tower illusion works with any image of a receding tower, or other receding object, such as the identical pair of photographs of tram lines.

Identical images of tram lines that appear to run in different directions.
These are actually identical images of parallel train tracks. Although the angles are the same in both images, the brain perceives them as being quite different.

A Turn in the Road

It shows three images, two of which match with a third one mismatching.

The two parallel tram lines are perceived to converge in the distance, as expected.

If the two parallel tram lines do not converge as they recede in the distance, the brain mistakenly perceives them as nonparallel and diverging.

Elongated cube drawn with parallel sides

Leaning tower illusion: Elongated cube drawn with parallel side

The illusion found with side-by-side replicas of an image of a receding object applies also to a single object, as in this figure. The figure is drawn with parallel sides, yet the impression is of an object that becomes fatter with distance.

Two parallel lines are perceived to converge in the distance

Left image: two parallel tram lines appear to converge in the distance, as expected.
Right: The image on the right is a vertical flip of image on the left, i.e., an upside down image. The brain doesn't know what to make of lt.

Studies of perception show the importance of being "Right Side Up". Go To Right Side Up

The Petronas Twin Towers in Kuala Lumpur

The leaning tower illusion shows that the brain uses the convergence angle of two reclining objects as they recede into the distance to calculate the relative angle between them. When two parallel towers appear in the same photograph, such as the Petronas Twin Towers in Kuala Lumpur,we perceive them as parallel because they appear to converge in the distance as they recede.

Japanese manga girls

Japanese girl doll vs Leaning tower illusion

The leaning tower illusion does not occur when viewing two leaning Japanese manga girls, even though the two cartoon images are tilted. The reason is that the cartoon girls do not appear to recede in depth, so our brain does not expect that they would converge in the distance. This phenomenon demonstrates that the brain applies its depth perception tool kit only in specific situations.

Read at www.psy.ritsumei.ac.jp The explanation.

The Impossible Object

An impossible object (also known as an impossible figure or an undecidable figure) is a type of optical illusion. It consists of a two-dimensional figure which is instantly and subconsciously interpreted by the visual system as representing a projection of a three-dimensional object.
In most cases the impossibility becomes apparent after viewing the figure for a few seconds. However, the initial impression of a 3D object remains even after it has been contradicted. There are also more subtle examples of impossible objects where the impossibility does not become apparent spontaneously and it is necessary to consciously examine the geometry of the implied object to determine that it is impossible.
The unsettling nature of impossible objects occurs because of our natural desire to interpret 2D drawings as three-dimensional objects. This is why a drawing of a Necker cube would be most likely seen as a cube, rather than "two squares connected with diagonal lines, a square surrounded by irregular planar figures, or any other planar figure." With an impossible object, looking at different parts of the object makes one reassess the 3D nature of the object, which confuses the mind.
Impossible objects are of interest to psychologists, mathematicians and artists without falling entirely into any one discipline. (Wikipedia)

The Penrose triangle (Oscar Reutersvärd's optical illusion)

The Penrose triangle, also known as the Penrose tribar, or the impossible tribar, is an impossible object. It was first created by the Swedish artist Oscar Reutersvärd in 1934. The psychologist Lionel Penrose and his mathematician son Roger Penrose independently devised and popularised it in the 1950s, describing it as "impossibility in its purest form". It is featured prominently in the works of artist M. C. Escher, whose earlier depictions of impossible objects partly inspired it. (Wikipedia)

The Penrose triangle

The Penrose triangle in an artistic world.

Left: Cube A is 4-cubic higher than cube B.

The Penrose triangle is impossible to construct in a real 3-dimensional world.

The Penrose triangle is impossible to construct in a real 3-dimensional world. Some models of Penrose triangle have been constructed, such that when they are viewed from a very specific point, the illusion of an triangle is perceived.

Impossible triangle sculpture as an optical illusion

Although possible to represent in two dimensions, it is not geometrically possible for such an object to exist in the physical world. However some models of impossible objects have been constructed, such that when they are viewed from a very specific point, the illusion is maintained. (Wikipedia)

Impossible triangle sculpture as an optical illusion, East Perth, Western Australia
The tribar sculpture, when viewed from a certain angle, appears to be the Penrose triangle. The term "Penrose triangle" can thus refer to the 2-dimensional depiction of the 3-D impossible triangle.

Impossible staircase

it is a two-dimensional depiction of a staircase in which the stairs make four 90-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.

Impossible staircase

Impossible staircase See it at Youtube

Left:The Construction of Impossible staircase.
When viewed from a certain angle, the illusion of an impossible staircase can be perceived.
First model of the 'impossible staircase', designed and constructed by Roger Penrose and Lionel Sharples Penrose FRS, England, 1955-1959.
Right: Impossible fall.

The Construction of Impossible staircase.

Impossible Greyscale figure

Impossible Figure

Right Side Up (Thatcher effect)

THE LENS IN YOUR EYE casts an upside-down image on your retina, but you see the world upright.
The Thatcher effect or Thatcher illusion is a phenomenon where it becomes more difficult to detect local feature changes in an upside-down face, despite identical changes being obvious in an upright face. It is named after the former British Prime Minister Margaret Thatcher, on whose photograph the effect was first and most famously demonstrated. The effect was originally created by Psychology Professor Peter Thompson in 1980. (Wikipedia)

Upside Down Perception of Image

George Bush ---------- Margaret Thatcher

If you look at the upside-down images of Bush’s and Thatcher's faces, you see nothing odd. But turn the same images right side up, and you see how grotesque they really look.

Right Side Up Images

Upside Down Perception of Expression

The Right Side Up effect is illustrated very simply in the cartoon faces. Upside down, it is hard to see their expressions even though you still see them as faces. (You can logically deduce which is smiling and which is frowning, but that is not the result of perception.) Turn them right side up, and the expressions are clearly recognized as if by magic.

Right Side Up Images

Hidden Photo Optical Illusion

Hidden Photo Optical Illusion (Shake your head illusion)
If you shake your head from side to side while staring at the vertical lines - you should see something interesting.

Hidden Photo Optical Illusion (Shake your head illusion)
If you shake your head from side to side while staring at the vertical lines - you should see John Lennon.

Hidden Photo Optical Illusion

Hidden Photo Optical Illusion (Image-size illusion)
If you decrease the image size - you should see something interesting.
Click here to see smaller image Click here to see smallest image of Michael Jackson