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Optical illusion

This article is about visual perception. For the album, see Optical Illusion (Time Requiem album).

Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect (where, despite movement, position remains unchanged). An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.

The checker shadow illusion. Although square A appears a darker shade of gray than square B, in the image the two have exactly the same luminance.
Drawing a connecting bar between the two squares breaks the illusion and shows that they are the same shade.
Gregory's categorization of illusions
In this animation, Mach bands exaggerate the contrast between edges of the slightly differing shades of gray as soon as they come in contact with one another.

Pathological visual illusions arise from pathological changes in the physiological visual perception mechanisms causing the aforementioned types of illusions; they are discussed e.g. under visual hallucinations.

Optical illusions, as well as multi-sensory illusions involving visual perception, can also be used in the monitoring and rehabilitation of some psychological disorders, including phantom limb syndrome and schizophrenia.

Contents

A familiar phenomenon and example for a physical visual illusion is when mountains appear to be much nearer in clear weather with low humidity (Foehn) than they are. This is because haze is a cue for depth perception, signalling the distance of far-away objects (Aerial perspective).

The classical example of a physical illusion is when a stick that is half immersed in water appears bent. This phenomenon was discussed by Ptolemy (ca. 150) and was often a prototypical example for an illusion.

Physiological illusions, such as the afterimages following bright lights, or adapting stimuli of excessively longer alternating patterns (contingent perceptual aftereffect), are presumed to be the effects on the eyes or brain of excessive stimulation or interaction with contextual or competing stimuli of a specific type—brightness, color, position, tile, size, movement, etc. The theory is that a stimulus follows its individual dedicated neural path in the early stages of visual processing and that intense or repetitive activity in that or interaction with active adjoining channels causes a physiological imbalance that alters perception.

The Hermann grid illusion and Mach bands are two illusions that are often explained using a biological approach. Lateral inhibition, where in receptive fields of the retina receptor signals from light and dark areas compete with one another, has been used to explain why we see bands of increased brightness at the edge of a color difference when viewing Mach bands. Once a receptor is active, it inhibits adjacent receptors. This inhibition creates contrast, highlighting edges. In the Hermann grid illusion, the gray spots that appear at the intersections at peripheral locations are often explained to occur because of lateral inhibition by the surround in larger receptive fields. However, lateral inhibition as an explanation of the Hermann grid illusion has been disproved. More recent empirical approaches to optical illusions have had some success in explaining optical phenomena with which theories based on lateral inhibition have struggled.

"The Organ Player" – Pareidolia phenomenon in Neptune's Grotto stalactite cave (Alghero, Sardinia)

Cognitive illusions are assumed to arise by interaction with assumptions about the world, leading to "unconscious inferences", an idea first suggested in the 19th century by the German physicist and physician Hermann Helmholtz. Cognitive illusions are commonly divided into ambiguous illusions, distorting illusions, paradox illusions, or fiction illusions.

Perceptual organization

Reversible figures and vase, or the figure-ground illusion

To make sense of the world it is necessary to organize incoming sensations into information which is meaningful. Gestalt psychologists believe one way this is done is by perceiving individual sensory stimuli as a meaningful whole. Gestalt organization can be used to explain many illusions including the rabbit–duck illusion where the image as a whole switches back and forth from being a duck then being a rabbit and why in the figure–ground illusion the figure and ground are reversible.

In addition, gestalt theory can be used to explain the illusory contours in the Kanizsa's triangle. A floating white triangle, which does not exist, is seen. The brain has a need to see familiar simple objects and has a tendency to create a "whole" image from individual elements. Gestalt means "form" or "shape" in German. However, another explanation of the Kanizsa's triangle is based in evolutionary psychology and the fact that in order to survive it was important to see form and edges. The use of perceptual organization to create meaning out of stimuli is the principle behind other well-known illusions including impossible objects. The brain makes sense of shapes and symbols putting them together like a jigsaw puzzle, formulating that which is not there to that which is believable.

The gestalt principles of perception govern the way different objects are grouped. Good form is where the perceptual system tries to fill in the blanks in order to see simple objects rather than complex objects. Continuity is where the perceptual system tries to disambiguate which segments fit together into continuous lines. Proximity is where objects that are close together are associated. Similarity is where objects that are similar are seen as associated. Some of these elements have been successfully incorporated into quantitative models involving optimal estimation or Bayesian inference.

The double-anchoring theory, a popular but recent theory of lightness illusions, states that any region belongs to one or more frameworks, created by gestalt grouping principles, and within each frame is independently anchored to both the highest luminance and the surround luminance. A spot's lightness is determined by the average of the values computed in each framework.

Depth and motion perception

The vertical–horizontal illusion where the vertical line is thought to be longer than the horizontal

Illusions can be based on an individual's ability to see in three dimensions even though the image hitting the retina is only two dimensional. The Ponzo illusion is an example of an illusion which uses monocular cues of depth perception to fool the eye. But even with two-dimensional images, the brain exaggerates vertical distances when compared with horizontal distances, as in the vertical-horizontal illusion where the two lines are exactly the same length.

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, although the two images hitting the retina are the same size. The optical illusion seen in a diorama/false perspective also exploits assumptions based on monocular cues of depth perception. The M.C. Escher painting Waterfall exploits rules of depth and proximity and our understanding of the physical world to create an illusion. Like depth perception, motion perception is responsible for a number of sensory illusions. Film animation is based on the illusion that the brain perceives a series of slightly varied images produced in rapid succession as a moving picture. Likewise, when we are moving, as we would be while riding in a vehicle, stable surrounding objects may appear to move. We may also perceive a large object, like an airplane, to move more slowly than smaller objects, like a car, although the larger object is actually moving faster. The phi phenomenon is yet another example of how the brain perceives motion, which is most often created by blinking lights in close succession.

The ambiguity of direction of motion due to lack of visual references for depth is shown in the spinning dancer illusion. The spinning dancer appears to be moving clockwise or counterclockwise depending on spontaneous activity in the brain where perception is subjective. Recent studies show on the fMRI that there are spontaneous fluctuations in cortical activity while watching this illusion, particularly the parietal lobe because it is involved in perceiving movement.

Color and brightness constancies

Simultaneous contrast illusion. The background is a color gradient and progresses from dark gray to light gray. The horizontal bar appears to progress from light grey to dark grey, but is in fact just one color.

Perceptual constancies are sources of illusions. Color constancy and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of light or color of light reflecting from it. An illusion of color difference or luminosity difference can be created when the luminosity or color of the area surrounding an unfamiliar object is changed. The luminosity of the object will appear brighter against a black field (that reflects less light) than against a white field, even though the object itself did not change in luminosity. Similarly, the eye will compensate for color contrast depending on the color cast of the surrounding area.

In addition to the gestalt principles of perception, water-color illusions contribute to the formation of optical illusions. Water-color illusions consist of object-hole effects and coloration. Object-hole effects occur when boundaries are prominent where there is a figure and background with a hole that is 3D volumetric in appearance. Coloration consists of an assimilation of color radiating from a thin-colored edge lining a darker chromatic contour. The water-color illusion describes how the human mind perceives the wholeness of an object such as top-down processing. Thus, contextual factors play into perceiving the brightness of an object.

Object

"Shepard's tables" deconstructed. The two tabletops appear to be different, but they are the same size and shape.

Just as it perceives color and brightness constancies, the brain has the ability to understand familiar objects as having a consistent shape or size. For example, a door is perceived as a rectangle regardless of how the image may change on the retina as the door is opened and closed. Unfamiliar objects, however, do not always follow the rules of shape constancy and may change when the perspective is changed. The "Shepard's table" illusion is an example of an illusion based on distortions in shape constancy.

Future perception

[dubiousdiscuss]

Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York has a more imaginative take on optical illusions, saying that they are due to a neural lag which most humans experience while awake. When light hits the retina, about one-tenth of a second goes by before the brain translates the signal into a visual perception of the world. Scientists have known of the lag, yet they have debated how humans compensate, with some proposing that our motor system somehow modifies our movements to offset the delay.

Changizi asserts that the human visual system has evolved to compensate for neural delays by generating images of what will occur one-tenth of a second into the future. This foresight enables humans to react to events in the present, enabling humans to perform reflexive acts like catching a fly ball and to maneuver smoothly through a crowd. In an interview with ABC Changizi said, "Illusions occur when our brains attempt to perceive the future, and those perceptions don't match reality." For example, an illusion called the Hering illusion looks like bicycle spokes around a central point, with vertical lines on either side of this central, so-called vanishing point. The illusion tricks us into thinking we are looking at a perspective picture, and thus according to Changizi, switches on our future-seeing abilities. Since we aren't actually moving and the figure is static, we misperceive the straight lines as curved ones. Changizi said:

Evolution has seen to it that geometric drawings like this elicit in us premonitions of the near future. The converging lines toward a vanishing point (the spokes) are cues that trick our brains into thinking we are moving forward—as we would in the real world, where the door frame (a pair of vertical lines) seems to bow out as we move through it—and we try to perceive what that world will look like in the next instant.

A pathological visual illusion is a distortion of a real external stimulus and are often diffuse and persistent. Pathological visual illusions usually occur throughout the visual field, suggesting global excitability or sensitivity alterations. Alternatively visual hallucination is the perception of an external visual stimulus where none exists. Visual hallucinations are often from focal dysfunction and are usually transient.

Types of visual illusions include oscillopsia, halos around objects, illusory palinopsia (visual trailing, light streaking, prolonged indistinct afterimages), akinetopsia, visual snow, micropsia, macropsia, teleopsia, pelopsia, metamorphopsia, dyschromatopsia, intense glare, blue field entoptic phenomenon, and purkinje trees.

These symptoms may indicate an underlying disease state and necessitate seeing a medical practitioner. Etiologies associated with pathological visual illusions include multiple types of ocular disease, migraines, hallucinogen persisting perception disorder, head trauma, and prescription drugs. If a medical work-up does not reveal a cause of the pathological visual illusions, the idiopathic visual disturbances could be analogous to the altered excitability state seen in visual aura with no migraine headache. If the visual illusions are diffuse and persistent, they often affect the patient's quality of life. These symptoms are often refractory to treatment and may be caused by any of the aforementioned etiologies, but are often idiopathic. There is no standard treatment for these visual disturbances.

The rubber hand illusion (RHI)

A visual representation of what an amputee with phantom limb syndrome senses.

The rubber hand illusion (RHI), a multi-sensory illusion involving both visual perception and touch, has been used to study how phantom limb syndrome affects amputees over time. Amputees with the syndrome actually responded to RHI more strongly than controls, an effect that was often consistent for both the sides of the intact and the amputated arm. However, in some studies, amputees actually had stronger responses to RHI on their intact arm, and more recent amputees responded to the illusion better than amputees who had been missing an arm for years or more. Researchers believe this is a sign that the body schema, or an individual's sense of their own body and its parts, progressively adapts to the post-amputation state. Essentially, the amputees were learning to no longer respond to sensations near what had once been their arm. As a result, many have suggested the use of RHI as a tool for monitoring an amputee's progress in reducing their phantom limb sensations and adjusting to the new state of their body.

Other research used RHI in the rehabilitation of amputees with prosthetic limbs. After prolonged exposure to RHI, the amputees gradually stopped feeling a dissociation between the prosthetic (which resembled the rubber hand) and the rest of their body. This was thought to be because they adjusted to responding to and moving a limb that did not feel as connected to the rest of their body or senses.

RHI may also be used to diagnose certain disorders related to impaired proprioception or impaired sense of touch in non-amputees.

Illusions and schizophrenia

Top-down processing involves using action plans to make perceptual interpretations and vice versa. (This is impaired in schizophrenia.)

Schizophrenia, a mental disorder often marked by hallucinations, also decreases a person's ability to perceive high-order optical illusions. This is because schizophrenia impairs one's capacity to perform top-down processing and a higher-level integration of visual information beyond the primary visual cortex, V1. Understanding how this specifically occurs in the brain may help in understanding how visual distortions, beyond imaginary hallucinations, affect schizophrenic patients. Additionally, evaluating the differences between how schizophrenic patients and normal individuals see illusions may enable researchers to better identify where specific illusions are processed in the visual streams.

An example of the hollow face illusion which makes concave masks appear to be jutting out (or convex).
An example of motion induced blindness: while fixating on the flashing dot, the stationary dots may disappear due to the brain prioritizing motion information.

One study on schizophrenic patients found that they were extremely unlikely to be fooled by a three dimensional optical illusion, the hollow face illusion, unlike neurotypical volunteers. Based on fMRI data, researchers concluded that this resulted from a disconnect between their systems for bottom-up processing of visual cues and top-down interpretations of those cues in the parietal cortex. In another study on the motion-induced blindness (MIB) illusion (pictured right), schizophrenic patients continued to perceive stationary visual targets even when observing distracting motion stimuli, unlike neurotypical controls, who experienced motion induced blindness. The schizophrenic test subjects demonstrated impaired cognitive organization, meaning they were less able to coordinate their processing of motion cues and stationary image cues.

There are a variety of different types of optical illusions. Many are included in the following list.

Ambigram tessellation "Escher" using negative space to reveal letters upside down.

Artists who have worked with optical illusions include M. C. Escher, Bridget Riley, Salvador Dalí, Giuseppe Arcimboldo, Patrick Bokanowski, Marcel Duchamp, Jasper Johns, Oscar Reutersvärd, Victor Vasarely and Charles Allan Gilbert. Contemporary artists who have experimented with illusions include Jonty Hurwitz, Sandro del Prete, Octavio Ocampo, Dick Termes, Shigeo Fukuda, Patrick Hughes, István Orosz, Rob Gonsalves, Gianni A. Sarcone, Ben Heine and Akiyoshi Kitaoka. Optical illusion is also used in film by the technique of forced perspective.

Op art is a style of art that uses optical illusions to create an impression of movement, or hidden images and patterns. Trompe-l'œil uses realistic imagery to create the optical illusion that depicted objects exist in three dimensions.

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The hypothesis claims that visual illusions occur because the neural circuitry in our visual system evolves, by neural learning, to a system that makes very efficient interpretations of usual 3D scenes based in the emergence of simplified models in our brain that speed up the interpretation process but give rise to optical illusions in unusual situations. In this sense, the cognitive processes hypothesis can be considered a framework for an understanding of optical illusions as the signature of the empirical statistical way vision has evolved to solve the inverse problem.

Research indicates that 3D vision capabilities emerge and are learned jointly with the planning of movements. That is, as depth cues are better perceived, individuals can develop more efficient patterns of movement and interaction within the 3D environment around them. After a long process of learning, an internal representation of the world emerges that is well-adjusted to the perceived data coming from closer objects. The representation of distant objects near the horizon is less "adequate".[further explanation needed] In fact, it is not only the Moon that seems larger when we perceive it near the horizon. In a photo of a distant scene, all distant objects are perceived as smaller than when we observe them directly using our vision.

Some images need to be viewed in full resolution to see their effect.
  • Motion aftereffect: this video produces a distortion illusion when the viewer looks away after watching it.

  • Ebbinghaus illusion: the orange circle on the left appears smaller than that on the right, but they are in fact the same size.

  • Café wall illusion: the parallel horizontal lines in this image appear sloped.

  • Checker version: the diagonal checker squares at the larger grid points make the grid appear distorted.

  • Checker version with horizontal and vertical central symmetry

  • Lilac chaser: if the viewer focuses on the black cross in the center, the location of the disappearing dot appears green.

  • Motion illusion: contrasting colors create the illusion of motion.

  • Watercolor illusion: this shape's yellow and blue border create the illusion of the object being pale yellow rather than white

  • Subjective cyan filter, left: subjectively constructed cyan square filter above blue circles, right: small cyan circles inhibit filter construction

  • Pinna's illusory intertwining effect and Pinna illusion (scholarpedia).(The picture shows squares spiralling in, although they are arranged in concentric circles.)

  • Optical illusion disc which is spun displaying the illusion of motion of a man bowing and a woman curtsying to each other in a circle at the outer edge of the disc, 1833

  • A hybrid image constructed from low-frequency components of a photograph of Marilyn Monroe (left inset) and high-frequency components of a photograph of Albert Einstein (right inset). The Einstein image is clearer in .

  • An ancient Roman geometric mosaic. The cubic texture induces a Necker-cube-like optical illusion.

  • A set of colorful spinning disks that create illusion. The disks appear to move backwards and forwards in different regions.

  • Pinna-Brelstaff illusion: the two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.

  • The Spinning Dancer appears to move both clockwise and counter-clockwise

  • Forced perspective: the man is made to appear to be supporting the Leaning Tower of Pisa in the background.

  • Scintillating grid illusion: Dark dots seem to appear and disappear rapidly at random intersections, hence the label "scintillating".

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Optical illusion
Optical illusion Language Watch Edit 160 160 Redirected from Visual illusion This article is about visual perception For the album see Optical Illusion Time Requiem album Within visual perception an optical illusion also called a visual illusion 2 is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality Illusions come in a wide variety their categorization is difficult because the underlying cause is often not clear 3 but a classification 1 4 proposed by Richard Gregory is useful as an orientation According to that there are three main classes physical physiological and cognitive illusions and in each class there are four kinds Ambiguities distortions paradoxes and fictions 4 A classical example for a physical distortion would be the apparent bending of a stick half immerged in water an example for a physiological paradox is the motion aftereffect where despite movement position remains unchanged 4 An example for a physiological fiction is an afterimage 4 Three typical cognitive distortions are the Ponzo Poggendorff and Muller Lyer illusion 4 Physical illusions are caused by the physical environment e g by the optical properties of water 4 Physiological illusions arise in the eye or the visual pathway e g from the effects of excessive stimulation of a specific receptor type 4 Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known 4 The checker shadow illusion Although square A appears a darker shade of gray than square B in the image the two have exactly the same luminance Drawing a connecting bar between the two squares breaks the illusion and shows that they are the same shade Gregory s categorization of illusions 1 In this animation Mach bands exaggerate the contrast between edges of the slightly differing shades of gray as soon as they come in contact with one another Pathological visual illusions arise from pathological changes in the physiological visual perception mechanisms causing the aforementioned types of illusions they are discussed e g under visual hallucinations Optical illusions as well as multi sensory illusions involving visual perception can also be used in the monitoring and rehabilitation of some psychological disorders including phantom limb syndrome 5 and schizophrenia 6 Contents 1 Physical visual illusions 2 Physiological visual illusions 3 Cognitive illusions 4 Explanation of cognitive illusions 4 1 Perceptual organization 4 2 Depth and motion perception 4 3 Color and brightness constancies 4 4 Object 4 5 Future perception 5 Pathological visual illusions distortions 6 Connections to psychological disorders 6 1 The rubber hand illusion RHI 6 2 Illusions and schizophrenia 7 List of illusions 8 In art 9 Cognitive processes hypothesis 10 Gallery 11 See also 12 Notes 13 References 14 Further reading 15 External linksPhysical visual illusions EditA familiar phenomenon and example for a physical visual illusion is when mountains appear to be much nearer in clear weather with low humidity Foehn than they are This is because haze is a cue for depth perception signalling the distance of far away objects Aerial perspective The classical example of a physical illusion is when a stick that is half immersed in water appears bent This phenomenon was discussed by Ptolemy ca 150 7 and was often a prototypical example for an illusion Physiological visual illusions EditPhysiological illusions such as the afterimages 8 following bright lights or adapting stimuli of excessively longer alternating patterns contingent perceptual aftereffect are presumed to be the effects on the eyes or brain of excessive stimulation or interaction with contextual or competing stimuli of a specific type brightness color position tile size movement etc The theory is that a stimulus follows its individual dedicated neural path in the early stages of visual processing and that intense or repetitive activity in that or interaction with active adjoining channels causes a physiological imbalance that alters perception The Hermann grid illusion and Mach bands are two illusions that are often explained using a biological approach Lateral inhibition where in receptive fields of the retina receptor signals from light and dark areas compete with one another has been used to explain why we see bands of increased brightness at the edge of a color difference when viewing Mach bands Once a receptor is active it inhibits adjacent receptors This inhibition creates contrast highlighting edges In the Hermann grid illusion the gray spots that appear at the intersections at peripheral locations are often explained to occur because of lateral inhibition by the surround in larger receptive fields 9 However lateral inhibition as an explanation of the Hermann grid illusion has been disproved 10 11 12 13 14 More recent empirical approaches to optical illusions have had some success in explaining optical phenomena with which theories based on lateral inhibition have struggled 15 Cognitive illusions Edit The Organ Player Pareidolia phenomenon in Neptune s Grotto stalactite cave Alghero Sardinia Cognitive illusions are assumed to arise by interaction with assumptions about the world leading to unconscious inferences an idea first suggested in the 19th century by the German physicist and physician Hermann Helmholtz 16 Cognitive illusions are commonly divided into ambiguous illusions distorting illusions paradox illusions or fiction illusions Ambiguous illusions are pictures or objects that elicit a perceptual switch between the alternative interpretations The Necker cube is a well known example other instances are the Rubin vase and the squircle based on Kokichi Sugihara s ambiguous cylinder illusion 17 Distorting or geometrical optical illusions are characterized by distortions of size length position or curvature A striking example is the Cafe wall illusion Other examples are the famous Muller Lyer illusion and Ponzo illusion Paradox illusions or impossible object illusions are generated by objects that are paradoxical or impossible such as the Penrose triangle or impossible staircase seen for example in M C Escher s Ascending and Descending and Waterfall The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join Fictions are when a figure is perceived even though it is not in the stimulus like with the Kanizsa triangle using illusory contours 18 19 Explanation of cognitive illusions EditPerceptual organization Edit Reversible figures and vase or the figure ground illusion Rabbit duck illusion To make sense of the world it is necessary to organize incoming sensations into information which is meaningful Gestalt psychologists believe one way this is done is by perceiving individual sensory stimuli as a meaningful whole 20 Gestalt organization can be used to explain many illusions including the rabbit duck illusion where the image as a whole switches back and forth from being a duck then being a rabbit and why in the figure ground illusion the figure and ground are reversible Kanizsa s triangle In addition gestalt theory can be used to explain the illusory contours in the Kanizsa s triangle A floating white triangle which does not exist is seen The brain has a need to see familiar simple objects and has a tendency to create a whole image from individual elements 20 Gestalt means form or shape in German However another explanation of the Kanizsa s triangle is based in evolutionary psychology and the fact that in order to survive it was important to see form and edges The use of perceptual organization to create meaning out of stimuli is the principle behind other well known illusions including impossible objects The brain makes sense of shapes and symbols putting them together like a jigsaw puzzle formulating that which is not there to that which is believable The gestalt principles of perception govern the way different objects are grouped Good form is where the perceptual system tries to fill in the blanks in order to see simple objects rather than complex objects Continuity is where the perceptual system tries to disambiguate which segments fit together into continuous lines Proximity is where objects that are close together are associated Similarity is where objects that are similar are seen as associated Some of these elements have been successfully incorporated into quantitative models involving optimal estimation or Bayesian inference 21 22 The double anchoring theory a popular but recent theory of lightness illusions states that any region belongs to one or more frameworks created by gestalt grouping principles and within each frame is independently anchored to both the highest luminance and the surround luminance A spot s lightness is determined by the average of the values computed in each framework 23 Depth and motion perception Edit The vertical horizontal illusion where the vertical line is thought to be longer than the horizontal Ponzo illusion Illusions can be based on an individual s ability to see in three dimensions even though the image hitting the retina is only two dimensional The Ponzo illusion is an example of an illusion which uses monocular cues of depth perception to fool the eye But even with two dimensional images the brain exaggerates vertical distances when compared with horizontal distances as in the vertical horizontal illusion where the two lines are exactly the same length 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 although the two images hitting the retina are the same size The optical illusion seen in a diorama false perspective also exploits assumptions based on monocular cues of depth perception The M C Escher painting Waterfall exploits rules of depth and proximity and our understanding of the physical world to create an illusion Like depth perception motion perception is responsible for a number of sensory illusions Film animation is based on the illusion that the brain perceives a series of slightly varied images produced in rapid succession as a moving picture Likewise when we are moving as we would be while riding in a vehicle stable surrounding objects may appear to move We may also perceive a large object like an airplane to move more slowly than smaller objects like a car although the larger object is actually moving faster The phi phenomenon is yet another example of how the brain perceives motion which is most often created by blinking lights in close succession The ambiguity of direction of motion due to lack of visual references for depth is shown in the spinning dancer illusion The spinning dancer appears to be moving clockwise or counterclockwise depending on spontaneous activity in the brain where perception is subjective Recent studies show on the fMRI that there are spontaneous fluctuations in cortical activity while watching this illusion particularly the parietal lobe because it is involved in perceiving movement 24 Color and brightness constancies Edit Simultaneous contrast illusion The background is a color gradient and progresses from dark gray to light gray The horizontal bar appears to progress from light grey to dark grey but is in fact just one color Perceptual constancies are sources of illusions Color constancy and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of light or color of light reflecting from it An illusion of color difference or luminosity difference can be created when the luminosity or color of the area surrounding an unfamiliar object is changed The luminosity of the object will appear brighter against a black field that reflects less light than against a white field even though the object itself did not change in luminosity Similarly the eye will compensate for color contrast depending on the color cast of the surrounding area In addition to the gestalt principles of perception water color illusions contribute to the formation of optical illusions Water color illusions consist of object hole effects and coloration Object hole effects occur when boundaries are prominent where there is a figure and background with a hole that is 3D volumetric in appearance Coloration consists of an assimilation of color radiating from a thin colored edge lining a darker chromatic contour The water color illusion describes how the human mind perceives the wholeness of an object such as top down processing Thus contextual factors play into perceiving the brightness of an object 25 Object Edit Shepard s tables deconstructed The two tabletops appear to be different but they are the same size and shape Just as it perceives color and brightness constancies the brain has the ability to understand familiar objects as having a consistent shape or size For example a door is perceived as a rectangle regardless of how the image may change on the retina as the door is opened and closed Unfamiliar objects however do not always follow the rules of shape constancy and may change when the perspective is changed The Shepard s table illusion 26 is an example of an illusion based on distortions in shape constancy Future perception Edit dubious discuss Researcher Mark Changizi of Rensselaer Polytechnic Institute in New York has a more imaginative take on optical illusions saying that they are due to a neural lag which most humans experience while awake When light hits the retina about one tenth of a second goes by before the brain translates the signal into a visual perception of the world Scientists have known of the lag yet they have debated how humans compensate with some proposing that our motor system somehow modifies our movements to offset the delay 27 Changizi asserts that the human visual system has evolved to compensate for neural delays by generating images of what will occur one tenth of a second into the future This foresight enables humans to react to events in the present enabling humans to perform reflexive acts like catching a fly ball and to maneuver smoothly through a crowd 28 In an interview with ABC Changizi said Illusions occur when our brains attempt to perceive the future and those perceptions don t match reality 29 For example an illusion called the Hering illusion looks like bicycle spokes around a central point with vertical lines on either side of this central so called vanishing point 30 The illusion tricks us into thinking we are looking at a perspective picture and thus according to Changizi switches on our future seeing abilities Since we aren t actually moving and the figure is static we misperceive the straight lines as curved ones Changizi said Evolution has seen to it that geometric drawings like this elicit in us premonitions of the near future The converging lines toward a vanishing point the spokes are cues that trick our brains into thinking we are moving forward as we would in the real world where the door frame a pair of vertical lines seems to bow out as we move through it and we try to perceive what that world will look like in the next instant 28 Pathological visual illusions distortions EditA pathological visual illusion is a distortion of a real external stimulus 31 and are often diffuse and persistent Pathological visual illusions usually occur throughout the visual field suggesting global excitability or sensitivity alterations 32 Alternatively visual hallucination is the perception of an external visual stimulus where none exists 31 Visual hallucinations are often from focal dysfunction and are usually transient Types of visual illusions include oscillopsia halos around objects illusory palinopsia visual trailing light streaking prolonged indistinct afterimages akinetopsia visual snow micropsia macropsia teleopsia pelopsia metamorphopsia dyschromatopsia intense glare blue field entoptic phenomenon and purkinje trees These symptoms may indicate an underlying disease state and necessitate seeing a medical practitioner Etiologies associated with pathological visual illusions include multiple types of ocular disease migraines hallucinogen persisting perception disorder head trauma and prescription drugs If a medical work up does not reveal a cause of the pathological visual illusions the idiopathic visual disturbances could be analogous to the altered excitability state seen in visual aura with no migraine headache If the visual illusions are diffuse and persistent they often affect the patient s quality of life These symptoms are often refractory to treatment and may be caused by any of the aforementioned etiologies but are often idiopathic There is no standard treatment for these visual disturbances Connections to psychological disorders EditThe rubber hand illusion RHI Edit A visual representation of what an amputee with phantom limb syndrome senses The rubber hand illusion RHI a multi sensory illusion involving both visual perception and touch has been used to study how phantom limb syndrome affects amputees over time 5 Amputees with the syndrome actually responded to RHI more strongly than controls an effect that was often consistent for both the sides of the intact and the amputated arm 5 However in some studies amputees actually had stronger responses to RHI on their intact arm and more recent amputees responded to the illusion better than amputees who had been missing an arm for years or more 5 Researchers believe this is a sign that the body schema or an individual s sense of their own body and its parts progressively adapts to the post amputation state 5 Essentially the amputees were learning to no longer respond to sensations near what had once been their arm 5 As a result many have suggested the use of RHI as a tool for monitoring an amputee s progress in reducing their phantom limb sensations and adjusting to the new state of their body 5 Other research used RHI in the rehabilitation of amputees with prosthetic limbs 33 After prolonged exposure to RHI the amputees gradually stopped feeling a dissociation between the prosthetic which resembled the rubber hand and the rest of their body 33 This was thought to be because they adjusted to responding to and moving a limb that did not feel as connected to the rest of their body or senses 33 RHI may also be used to diagnose certain disorders related to impaired proprioception or impaired sense of touch in non amputees 33 Illusions and schizophrenia Edit Top down processing involves using action plans to make perceptual interpretations and vice versa This is impaired in schizophrenia Schizophrenia a mental disorder often marked by hallucinations also decreases a person s ability to perceive high order optical illusions 6 This is because schizophrenia impairs one s capacity to perform top down processing and a higher level integration of visual information beyond the primary visual cortex V1 6 Understanding how this specifically occurs in the brain may help in understanding how visual distortions beyond imaginary hallucinations affect schizophrenic patients 6 Additionally evaluating the differences between how schizophrenic patients and normal individuals see illusions may enable researchers to better identify where specific illusions are processed in the visual streams 6 An example of the hollow face illusion which makes concave masks appear to be jutting out or convex An example of motion induced blindness while fixating on the flashing dot the stationary dots may disappear due to the brain prioritizing motion information One study on schizophrenic patients found that they were extremely unlikely to be fooled by a three dimensional optical illusion the hollow face illusion unlike neurotypical volunteers 34 Based on fMRI data researchers concluded that this resulted from a disconnect between their systems for bottom up processing of visual cues and top down interpretations of those cues in the parietal cortex 34 In another study on the motion induced blindness MIB illusion pictured right schizophrenic patients continued to perceive stationary visual targets even when observing distracting motion stimuli unlike neurotypical controls who experienced motion induced blindness 35 The schizophrenic test subjects demonstrated impaired cognitive organization meaning they were less able to coordinate their processing of motion cues and stationary image cues 35 List of illusions EditThere are a variety of different types of optical illusions Many are included in the following list Main article List of optical illusionsIn art Edit Ambigram tessellation Escher using negative space to reveal letters upside down Artists who have worked with optical illusions include M C Escher 36 Bridget Riley Salvador Dali Giuseppe Arcimboldo Patrick Bokanowski Marcel Duchamp Jasper Johns Oscar Reutersvard Victor Vasarely and Charles Allan Gilbert Contemporary artists who have experimented with illusions include Jonty Hurwitz Sandro del Prete Octavio Ocampo Dick Termes Shigeo Fukuda Patrick Hughes Istvan Orosz Rob Gonsalves Gianni A Sarcone Ben Heine and Akiyoshi Kitaoka Optical illusion is also used in film by the technique of forced perspective Op art is a style of art that uses optical illusions to create an impression of movement or hidden images and patterns Trompe l œil uses realistic imagery to create the optical illusion that depicted objects exist in three dimensions Cognitive processes hypothesis EditThis section needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Optical illusion news newspapers books scholar JSTOR March 2019 Learn how and when to remove this template message The hypothesis claims that visual illusions occur because the neural circuitry in our visual system evolves by neural learning to a system that makes very efficient interpretations of usual 3D scenes based in the emergence of simplified models in our brain that speed up the interpretation process but give rise to optical illusions in unusual situations In this sense the cognitive processes hypothesis can be considered a framework for an understanding of optical illusions as the signature of the empirical statistical way vision has evolved to solve the inverse problem 37 Research indicates that 3D vision capabilities emerge and are learned jointly with the planning of movements 38 That is as depth cues are better perceived individuals can develop more efficient patterns of movement and interaction within the 3D environment around them 38 After a long process of learning an internal representation of the world emerges that is well adjusted to the perceived data coming from closer objects The representation of distant objects near the horizon is less adequate further explanation needed In fact it is not only the Moon that seems larger when we perceive it near the horizon In a photo of a distant scene all distant objects are perceived as smaller than when we observe them directly using our vision Gallery EditSome images need to be viewed in full resolution to see their effect Play media Motion aftereffect this video produces a distortion illusion when the viewer looks away after watching it Ebbinghaus illusion the orange circle on the left appears smaller than that on the right but they are in fact the same size Cafe wall illusion the parallel horizontal lines in this image appear sloped Checker version the diagonal checker squares at the larger grid points make the grid appear distorted Checker version with horizontal and vertical central symmetry Lilac chaser if the viewer focuses on the black cross in the center the location of the disappearing dot appears green Motion illusion contrasting colors create the illusion of motion Watercolor illusion this shape s yellow and blue border create the illusion of the object being pale yellow rather than white 39 Subjective cyan filter left subjectively constructed cyan square filter above blue circles right small cyan circles inhibit filter construction 40 41 Pinna s illusory intertwining effect 42 and Pinna illusion scholarpedia 43 The picture shows squares spiralling in although they are arranged in concentric circles Optical illusion disc which is spun displaying the illusion of motion of a man bowing and a woman curtsying to each other in a circle at the outer edge of the disc 1833 A hybrid image constructed from low frequency components of a photograph of Marilyn Monroe left inset and high frequency components of a photograph of Albert Einstein right inset The Einstein image is clearer in the full image An ancient Roman geometric mosaic The cubic texture induces a Necker cube like optical illusion Play media A set of colorful spinning disks that create illusion The disks appear to move backwards and forwards in different regions Pinna Brelstaff illusion the two circles seem to move when the viewer s head is moving forwards and backwards while looking at the black dot 44 The Spinning Dancer appears to move both clockwise and counter clockwise Forced perspective the man is made to appear to be supporting the Leaning Tower of Pisa in the background Scintillating grid illusion Dark dots seem to appear and disappear rapidly at random intersections hence the label scintillating See also EditAuditory illusion Barberpole illusion Barber s pole Camouflage Chronostasis stopped clock illusion Closed eye hallucination visualization Contour rivalry Emmert s law Flashed face distortion effect Fraser spiral illusion Gravity hill Human reactions to infrasound Hidden faces Infinity edge pool Kinetic depth effect Mirage Multistable perception Rabbit duck illusion Silencing The dress Troxler s fading Visual space Watercolour illusionNotes Edit a b Gregory Richard 1991 Putting illusions in their place Perception 20 1 1 4 doi 10 1068 p200001 PMID 1945728 S2CID 5521054 In the scientific literature the term visual illusion is preferred because the older term gives rise to the assumption that the optics of the eye were the general cause for illusions which is only the case for so called physical illusions Optical in the term derives from the Greek optein seeing so the term refers to an illusion of seeing not to optics as a branch of modern physics A regular scientific source for illusions are the journals Perception and i Perception Bach Michael Poloschek C M 2006 Optical Illusions PDF Adv Clin Neurosci Rehabil 6 2 20 21 a b c d e f g h Gregory Richard L 1997 Visual illusions classified PDF Trends in Cognitive Sciences 1 5 190 194 doi 10 1016 s1364 6613 97 01060 7 PMID 21223901 S2CID 42228451 a b c d e f g DeCastro Thiago Gomes Gomes William Barbosa 2017 05 25 Rubber Hand Illusion Evidence for a multisensory integration of proprioception Avances en Psicologia Latinoamericana 35 2 219 doi 10 12804 revistas urosario edu co apl a 3430 ISSN 2145 4515 a b c d e King Daniel J Hodgekins Joanne Chouinard Philippe A Chouinard Virginie Anne Sperandio Irene 2017 06 01 A review of abnormalities in the perception of visual illusions in schizophrenia Psychonomic Bulletin amp Review 24 3 734 751 doi 10 3758 s13423 016 1168 5 ISSN 1531 5320 Wade Nicholas J 1998 A natural history of vision Cambridge MA MIT Press After Images worqx com Archived from the original on 2015 04 22 Pinel J 2005 Biopsychology 6th ed Boston Allyn amp Bacon ISBN 0 205 42651 4 Lingelbach B Block B Hatzky B Reisinger E 1985 The Hermann grid illusion retinal or cortical Perception 14 1 A7 Geier J Bernath L 2004 Stopping the Hermann grid illusion by simple sine distortion Perception Malden Ma Blackwell pp 33 53 ISBN 978 0631224211 Schiller Peter H Carvey Christina E 2005 The Hermann grid illusion revisited Perception 34 11 1375 1397 doi 10 1068 p5447 PMID 16355743 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Insider Petry Susan Meyer Glenn E 2012 12 06 The Perception of Illusory Contours Springer 1987th edition p 696 ISBN 9781461247609 Gregory R L 1972 Cognitive Contours Nature 238 5358 51 52 Bibcode 1972Natur 238 51G doi 10 1038 238051a0 PMID 12635278 S2CID 4285883 Retrieved 2021 09 04 a b Myers D 2003 Psychology in Modules 7th ed New York Worth ISBN 0 7167 5850 4 Yoon Mo Jung and Jackie Jianhong Shen 2008 J Visual Comm Image Representation 19 1 42 55 First order modeling and stability analysis of illusory contours Yoon Mo Jung and Jackie Jianhong Shen 2014 arXiv 1406 1265 Illusory shapes via phase transition Archived 2017 11 24 at the Wayback Machine Bressan P 2006 The Place of White in a World of Grays A Double Anchoring Theory of Lightness Perception Psychological Review 113 3 526 553 doi 10 1037 0033 295x 113 3 526 PMID 16802880 Bernal B Guillen M amp Marquez J 2014 The spinning dancer illusion and spontaneous brain fluctuations An fMRI study Neurocase Psychology Press 20 6 627 639 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doi 10 1016 j neuroimage 2009 03 033 ISSN 1053 8119 PMID 19327402 S2CID 10008080 a b Tschacher Wolfgang Schuler Daniela Junghan Ulrich 2006 01 31 Reduced perception of the motion induced blindness illusion in schizophrenia Schizophrenia Research 81 2 261 267 doi 10 1016 j schres 2005 08 012 ISSN 0920 9964 PMID 16243490 S2CID 10752733 Seckel Al 2017 Masters of Deception Escher Dali amp the Artists of Optical Illusion Sterling p 320 ISBN 9781402705779 Gregory Richard L 1997 Knowledge in perception and illusion PDF Philosophical Transactions of the Royal Society of London Series B Biological Sciences 352 1358 1121 7 Bibcode 1997RSPTB 352 1121G doi 10 1098 rstb 1997 0095 PMC 1692018 PMID 9304679 Archived PDF from the original on 2005 04 04 a b Sweet Barbara Kaiser Mary August 2011 Depth Perception Cueing and Control PDF AIAA Modeling and Simulation Technologies Conference NASA Ames Research Center doi 10 2514 6 2011 6424 hdl 2060 20180007277 ISBN 978 1 62410 154 0 via American Institute of Aeronautics and Astronautics Bangio Pinna Gavin Brelstaff Lothar Spillman 2001 Surface color from boundaries a new watercolor illusion Vision Research 41 20 2669 2676 doi 10 1016 s0042 6989 01 00105 5 PMID 11520512 S2CID 16534759 Hoffmann Donald D 1998 Visual Intelligence How we create what we see Norton p 174 Stephen Grossberg Baingio Pinna 2012 Neural Dynamics of Gestalt Principles of Perceptual Organization From Grouping to Shape and Meaning PDF Gestalt Theory 34 3 4 399 482 Archived from the original PDF on 2013 10 04 Retrieved 2013 07 14 Pinna B Gregory R L 2002 Shifts of Edges and Deformations of Patterns Perception 31 12 1503 1508 doi 10 1068 p3112pp PMID 12916675 S2CID 220053062 CS1 maint multiple names authors list link Pinna Baingio 2009 Pinna illusion Scholarpedia 4 2 6656 Bibcode 2009SchpJ 4 6656P doi 10 4249 scholarpedia 6656 Baingio Pinna Gavin J Brelstaff 2000 A new visual illusion of relative motion PDF Vision Research 40 16 2091 2096 doi 10 1016 S0042 6989 00 00072 9 PMID 10878270 S2CID 11034983 Archived PDF from the original on 2013 10 05 References EditBach Michael Poloschek C M 2006 Optical Illusions PDF Adv Clin Neurosci Rehabil 6 2 20 21 Changizi Mark A Hsieh Andrew Nijhawan Romi Kanai Ryota Shimojo Shinsuke 2008 Perceiving the Present and a Systematization of Illusions PDF Cognitive Science 32 3 459 503 doi 10 1080 03640210802035191 PMID 21635343 Eagleman D M 2001 Visual Illusions and Neurobiology PDF Nature Reviews Neuroscience 2 12 920 6 doi 10 1038 35104092 PMID 11733799 S2CID 205023280 Gregory Richard 1991 Putting illusions in their place Perception 20 1 1 4 doi 10 1068 p200001 PMID 1945728 S2CID 5521054 Gregory Richard 1997 Knowledge in perception and illusion PDF Phil Trans R Soc Lond B 352 1358 1121 1128 Bibcode 1997RSPTB 352 1121G doi 10 1098 rstb 1997 0095 PMC 1692018 PMID 9304679 Purves D Lotto R B Nundy S 2002 Why We See What We Do American Scientist 90 3 236 242 doi 10 1511 2002 9 784 Purves D Williams M S Nundy S Lotto R B 2004 Perceiving the intensity of light Psychological Review 111 1 142 158 CiteSeerX 10 1 1 1008 6441 doi 10 1037 0033 295x 111 1 142 PMID 14756591 Renier L Laloyaux C Collignon O Tranduy D Vanlierde A Bruyer R De Volder A G 2005 The Ponzo illusion using auditory substitution of vision in sighted and early blind subjects Perception 34 7 857 867 doi 10 1068 p5219 PMID 16124271 S2CID 17265107 Renier L Bruyer R De Volder A G 2006 Vertical horizontal illusion present for sighted but not early blind humans using auditory substitution of vision Perception amp Psychophysics 68 4 535 542 doi 10 3758 bf03208756 PMID 16933419 Yang Z Purves D 2003 A statistical explanation of visual space Nature Neuroscience 6 6 632 640 doi 10 1038 nn1059 PMID 12754512 S2CID 610068 Dixon E Shapiro A Lu Z 2014 Scale Invariance in brightness illusions implicates object level visual processing Scientific Reports 4 3900 Bibcode 2014NatSR 4E3900D doi 10 1038 srep03900 PMC 3905277 PMID 24473496 Further reading EditPurves Dale et al 2008 Visual illusions An Empirical Explanation Scholarpedia 3 6 3706 Bibcode 2008SchpJ 3 3706P doi 10 4249 scholarpedia 3706 David Cycleback 2018 Understanding Human Minds and Their Limits Publisher Bookboon com ISBN 978 87 403 2286 6External links EditWikimedia Commons has media related to Optical illusion Optical illusionat Wikipedia s sister projects Definitions from Wiktionary Quotations from Wikiquote Data from Wikidata Retrieved from https en wikipedia org w index php title Optical illusion amp oldid 1053041205, wikipedia, wiki, book,

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