Optical illusion

An optical illusion or visual illusion is a perception deception of vision.

Optical illusions can affect virtually all aspects of vision. There are deep illusions, color illusions, geometric illusions, motion illusions, and some more. In all these cases, the visual system appears to be incorrect assumptions about the nature of the visual stimulus to hit as it can be shown with the aid of other senses, or by removing the triggering factors.

Optical illusions are examined in the psychology of perception, because from them conclusions about the processing of sensory stimuli in the brain can be obtained. Optical illusions are based on the fact that the perception is subjective and is influenced by the brain (see top-down and bottom-up ). Systematically produced and analyzed optical illusions in the Gestalt psychology.

Examples

Relativity of lines

The square in the image on the left consists of a chessboard arranged dark and light squares part. In some of the dark part of the square corners are disturbed by small bright squares. One gets the impression that the - demonstrably straight - lines that separate the squares part wavy curved. In this case, their brightness and thickness plays a significant role.

In the example on the right above the crossbar appear to be wedge-shaped - in truth, all horizontal lines exactly parallel and the horizontal stripes are rectangles.

This illusion was first described in 1874 by Hugo Münsterberg ( 1863-1916 ), which she found on an American Pferdebahnabokarte, and in 1894 /97 shifted checkerboard figure ( eccentric chess illusion ) published. You will therefore translate Münsterberg illusion. Other researchers such as AH Pierce called 1898 Kindergarten basketweave - deception ( illusion of the kindergarten patterns in Psychological Review No. 5, 233-253 ). The most recent name comes from Richard L. Gregory, who after a black and white tiled wall in a cafe in the 19th century in the city of Bristol as a coffee - deception ( "café wall illusion" ) described in 1973. After the Café Wall illusion McCourt can be explained by a brightness contrast. Are the rows of black and white fields separated by narrow gray lines, then take it between black squares as much brighter and darker true between light fields. The perception now combines the light appearing line segments with the corners of the bright fields and accordingly appear dark line segments with the corners of the dark fields. These subjective contours are perceived as inclined to the horizontal, and therefore let the rectangles appear wedge-shaped. The effect is not limited to a pattern of alternating black and white tiles, it occurs eg even with a stepped or continuous shading of tiles between black and white. The illusion is highly dependent on the width and the gray value of the dividing line and reaches its maximum when the width of the line by a factor of two to three smaller than the resolving power of the eye ( one minute of arc = 2.91 × 10-4 rad). The impression wavy extending boundaries may also arise when rows are combined with unequal period length. There are also colored versions.

In the fourth example (bottom right) gives the impression that the diagonal lines are curved, but in fact they are perfectly straight and parallel. This illusion is also called Zöllner illusion. Pigeons perceive this illusion in comparison to people exactly the opposite, they underestimate the angle between the lines.

Relativity of colors

If you long stares about half a minute on the green square in the image on the right and then to the free surface looks next to it, so it appears a reddish square. The reddish square arises because we see an afterimage on the retina. It has the complementary color to the green square.

Not everyone who is for the first time confronted with this coloration perceives. Apparently there are corrective measures that suppress this sensation. It may help if you stare a little longer, thereby adjusting the eyes to infinite range of vision.

Explanations for the occurrence of an afterimage can be found in the three-color theory and in the opponent color theory.

Relativity of brightness

The perception of brightness differences is very subjective. A shade of color that we perceive as light at dusk, appears dark in sunlight, and the other way around. Physically, this interpretation is incorrect. Our brain also engages when looking at the examples on the left and right side back on this experience. Links will appear gray when it is dark lighter, darker in bright conditions, although the gray bars everywhere has the same gray value.

The square B right in the picture is in the shade. Following the pattern it must be a white square, much brighter than the dark square are considered A. Absolutely but both equally bright squares

Overemphasis of contrasts

The Hermann grid were presented by Ludimar Hermann in 1870. Since this phenomenon was also noted by Ewald Hering, it is also designated as herring lattice. In the grid, the viewer believes to see the intersection of the gray lines black spots. They flicker and are only perceive as long as one does not focus his eyes on it.

Previously it was assumed that the over-emphasis of contrasts on the lateral inhibition is based. However, there is strong evidence to suggest that this theory is not applicable. If you change the deception only slightly, for example, by sinusoidal bars, the illusion disappears. This effect contradicts the theory of lateral inhibition.

Relativity of size

The picture at left is an example of many similar diagrams that confuse human perception. The left blue ball is smaller than the surrounding red in the right is reversed. The transfer of relatively small and relatively larger on the two blue balls in a direct comparison is wrong. Both blue balls are the same size.

The picture on the right shows a portico and three pairs of sisters. The couple in the foreground appears to be smaller than the average couple. The rear pair appears greatest.

A re-measurement shows that all three pairs of the same size. Our eye provides the image on the retina, but its meaning is only revealed by the processing of image information in the brain. Although the image is two dimensional, we see a path that runs from front to back and the impression of depth conveyed. We conclude that objects are at the bottom in our proximity and objects in the image center are further away from us.

The image processing in the brain is assumed that articles to be smaller with increasing distance. Therefore, we wonder not about the fact that the woman behind the right in red coat compared to the people left in the picture is extremely small. She's just further away than the people in the foreground.

The couple in the foreground is very small because the distance is interpreted as low. Would it be the same size as the central couple in reality, it would appear on the image larger. However, since it is exactly the same size as the middle pair on the image, the brain concludes that the people must be smaller in reality.

The same goes for the rear pair. Actually, its size would have the woman in red coat match. Instead, we see it in more than twice the size. Through our image processing process, these two people are in the background, consequently giants.

The relativity of size, is important in the Ponzo illusion. This illusion is also known as the Railway Lines illusion known as the figure is reminiscent of railroad tracks, and was developed by the Italian psychologist Mario Ponzo in 1913. Two bars are painted the same size run on two (or more lines ( like straight train tracks ). The top bar looks bigger. Principal explanation is the principle of size constancy. The converging rail lines as actually perceived parallel lines that have their vanishing point in great depth. This creates the impression of depth. the top bar is thereby perceived as further away due to the spatial interpretation and therefore would have to be actually much smaller than the lower bar to be perceived as equal. however, since the retinal images of both bars are the same size, the upper bar appears larger.

This optical illusion makes you look in architecture, photography and film, the term forced perspective to use to make objects appear larger or more distant in the eye of the beholder.

Relativity of perspective

Another type of optical illusion created by the angle of his head. Thus, objects can be designed which are perceived very differently from different angles. In the picture is shown on the right a strange arrangement of objects. If you look to the left in the mirror, it is believed to have a full wing on. On a similar effect based models representing the seemingly "impossible objects", such as the Penrose triangle.

Under the keyword " relativity of perspective " and the "wrong" Moon inclination can be arranged. This phenomenon can be observed when the moon and sun during the day to see the sky at the same time. One would expect that the moon 's illuminated side, the sickle, the sun turns, because it receives its light from there. Instead, giving way to the sickle with its axis of symmetry significantly and sometimes even strongly upwards from the expected direction. The crescent looking over the sun away, as the picture shows. Also unexpected is the sickle at night in spite of sunken sun sometimes upwards instead of down. This phenomenon is an Optical Illusion, for which there are different explanations, among other things, that the illusion depends on the viewing direction.

Nonexistent Objects

Spots, lines, cubes?

Kanizsa Triangle

In some sense impressions of the observer believes to perceive objects that are not present. An example of this is the opposite pattern ( left) in broken lines. The viewer feels at the interfaces to see white wheels.

In the example at the center of the viewer sees a cube. The edges that are not present in the picture, are complemented in the image processing in the brain. In the Kanizsa triangle (named after Gaetano Kanizsa ) in the far right believes the viewer to discover a white triangle, even though the picture shows only lines and circle segments. The imaginary lines are known in the literature as "cognitive contours " ( cognitive contours ).

Similarly, the canals of Mars or Mars face on the effort of the brain can be traced back to rediscover Familiar in pattern recognition.

Multiple perceived objects

Kippfiguren as the Necker cube is an example of multi- stable perception. The experience determines the position, in which the character is preferably performed. For prolonged viewing the image of the Necker cube flips.

Motion illusions

There is a long series of optical illusions, in which the viewer thinks that moving parts of the image. Here, the head itself does not need to be moved and sometimes sometimes. The latter variant works best with peripheral vision, that is, the movement can be seen in the places that are just not focused.

A motion illusion also occurs when one considers a small object in front of an environment that is no evidence of the spatial position. A lone star in the dark sky seems to move.

Also, can cause the illusion of movement, without moving his head static images. The cause is found in repeated patterns within which different contrasts are strong. Due to the different fast forwarding of different high contrast and brightness in the periphery of the retina occurs in the downstream levels of visual processing (keyword: Reichardt detectors ) for false processing and thus to misinterpretation. The " Rotating Snake" is a very good example.

Other examples

An Ames room, named after Adelbert Ames, Jr. (1880-1955), is a room with a special geometry in which can be implemented a number of optical illusions.

A number of other optical illusions are known partly since antiquity, partly described in the 19th century and in the recent past. These include:

• Anamorphosis
• Barber Pole Illusion
• Delboeuf Bluff
• Missing square puzzle
• Fraser Spiral
• Hollow -Face illusion
• Hybrid image
• Mach strips ( Ernst Mach, 1865)
• Moon Illusion
• Mueller- Lyer illusion (Franz Müller- Lyer, 1889)
• Poggendorff illusion (Johann Christian Poggendorff, 1860)
• Pulfrich effect (Carl Pulfrich, 1922)
• Converging lines and sun rays
• T- figure - illusion
• Impossible figure
• Picture puzzle
• Watercolor effect ( Pinna Baingio, John S. Werner and Lothar Spillmann, 2003)

Optical illusions in everyday life

The fact that optical illusions can also occur in everyday life, these examples show:

• In the film the fast concatenation of static frames creates the illusion of movement. It often seems as if the wheels of the car move backward, although it is not so. See stroboscopic effect.
• Under certain landscape conditions seem roads running downhill in reality to lead uphill and vice versa ( for example, the Electric Brae in Scotland).
• In the illusionistic painting rooms are optically enlarged by means of trompe l'oeil technique.
• The Op-Art sets optical illusions targeted as a stylistic device.

The border of the graphic is a rectangle, but it seems to taper to the right.

The image of the houndstooth pattern seems tilted to the right.

In this textile wallcovering is actually parallel lines seem to rejuvenate.

The text appears blurred, but in fact only additional parallel, sharp lines are drawn.

Possible explanation of optical illusions

A possible solution for " optical illusions " is the theory of the American Mark Changizi. This speaks of a " look into the future ", which makes our brain every second. The visual information from the outside world on the retina and reach the chiasm to the brain. However, sharp vision is possible only in a small part of the retina. When viewing a visual scene leads the eye targeted movements ( Willkürsakkaden ). The blurred images during eye movement will subconsciously hidden by the brain. From the different visual impressions of the pulses over a portion of the thalamus reach ( lateral geniculate body ) and then in the primary visual center at Hinterhauptspol, the primary visual center. However, there are already at this level, feedback loops, so that only about 10 % of the nerve fibers coming from the eye to the visual center. Already at this level is an essential pre-processing of the signals rather than due to biological parameters and previous experience. In essence, the brain thus creating the visual representation of what is seen from relatively weak signals itself, this mechanism is susceptible to problems, the optical illusions illustrate. The brain then evaluates the information and calculates the expected change in the future, this is seen evolutionarily important. For example, suggest vanishing points a movement, the brain calculates the new environment of it. Since the real position but does not change, creates the optical illusion that lines are bent. According to Changizi can thus explain up to 50 illusions.