The Psychology of Visual Illusion

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Sarah Mae Sincero Sep 10, Types of Illusions. Retrieved Jun 24, from Explorable. The text in this article is licensed under the Creative Commons-License Attribution 4. That is it. You can use it freely with some kind of link , and we're also okay with people reprinting in publications like books, blogs, newsletters, course-material, papers, wikipedia and presentations with clear attribution. Login Sign Up. Types of Illusion. Sarah Mae Sincero Discover 31 more articles on this topic. Don't miss these related articles:. Full reference:. Related articles Related pages:.

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8 Mind-Bending Optical Illusions (And What They Reveal About How Our Brains Work)

Leave this field blank :. Want to stay up to date? Follow us! Follow ExplorableMind. Footer bottom Explorable. Login Sign Up Privacy Policy. Search website. Complete Collection. Perhaps the best real-life example of a perceptual illusion is the Moon illusion. When the Moon is at the horizon, it appears to be much larger than it does when it is high in the sky. Yet when the Moon is photographed at various points across the sky, all the images on the negatives are the same size.

Considerable debate surrounds the source of the Moon illusion. Another explanation is that the lack of distance cues in the night sky causes the eyes to adjust to a near-focus position, which makes the high Moon appear smaller. Many sensory illusions may be described as the aftereffects of the stimulation, or overstimulation, of the senses.

Sensitivity in any of the senses may be measured as the just-perceptible intensity threshold , or limen of the appropriate stimulus. The smallest detectable stimulus is called the absolute threshold , while the smallest detectable change in the intensity of a stimulus is called the difference threshold.

Such thresholds can serve as points of reference, or anchors, against which subsequent stimuli are judged or perceived. Yet sensory anchors fluctuate within the same individual under different conditions, and in some cases they can mislead a person about the properties of subsequent stimuli. For example, two successive stimuli may be identical but nevertheless give the illusion of being different. The theory suggests that a physical trace in the form of temporarily excited nerve cells of an original stimulus remains in the brain even after that stimulus stops and that this trace influences the estimate or appreciation of a subsequent stimulus.

The strength of the trace, also called an aftereffect, and the speed of its disappearance vary greatly in individual cases.

Optical Illusions

People who are field dependent that is, who tend to observe a field in its totality are said to show weaker aftereffect traces. Conversely, field-independent subjects those who, by selective attention , are more likely to consider a specific stimulus apart from its context show stronger aftereffects. The normal human eye can detect about gradations of colour in the visible spectrum as in the rainbow , about 20 barely noticeable differences within a given colour, and about variations of brightness. However, when two spots of equally bright light are observed in close succession, the first intensity may seem brighter.

The first light may be said to serve the function of brightness adaptation or adjustment in the eye; therefore, the second light will fall on a partly adapted and therefore less sensitive retina. In a brief time, such excitement in the retina or even in the brain tends to subside, or fade. As a result of the fading traces of excitement, various hues of a given colour may appear to be lighter or darker when looked at successively.

Contrast-colour phenomena also may result from such fading traces. A successive contrast occurs when, after one has stared at a red surface, a green surface looks much brighter. As one enters a dark room from bright sunshine, the room at first seems quite dark by contrast.

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A simultaneous contrast occurs when an area of brightness is seen against a less intense or a more intense background. If a gray patch of paper is placed on a black background, it looks whiter than it did before; if placed on a white background, it looks darker. The felt perception of differences in weights received experimental attention in , when experiments indicated that a second weight feels either heavier or lighter than an immediately preceding identical weight.

This illusion results partially from the expectancy of the person doing the lifting. If the second weight is lifted quickly and easily, it will feel lighter than the first; if it comes up more slowly, it will feel heavier. Expectancy, or set, is also often invoked in efforts to explain the size-weight illusion, in which a large cardboard box feels lighter than a smaller box even though both weigh the same.

Smell olfactory discrimination is influenced by any odour to which the olfactory structures already have adapted. Receptors in the nose, however, adapt quickly and cease to respond to a particular stimulus. This effect is called olfactory fatigue. There also may be present the phenomenon of masking ; this is a decrease in sensitivity to one odour after exposure to another for example, a strong-smelling disinfectant. The human ear typically serves to distinguish between about 1, levels of pitch.

For loudness, differential-threshold studies reveal about separately perceived levels in the region of greatest auditory sensitivity about 1, to 4, cycles per second. For humans, the number of discriminable tones is in the hundred thousands. Yet when two sounds are heard in close succession, the intensity or loudness of the second is judged by comparing it with the first. The steady hum of an electric fan may help to diffuse the noises of traffic outside and thus improve the discrimination of sounds in the room.

It can happen, however, that a very warm stimulus will produce a sensation of cold when placed on a spot that responds to cold.

A "Psychological" Optical Illusion

Thus, when a warm stimulus is perceived as cold, the illusion is called paradoxical cold. Paradoxical heat, a less frequent experience, results from stimulating warm and cold spots simultaneously. The sensation is sometimes called psychological heat. Sudden temperature contrasts can play tricks on the tactile sense.

If hot water is run over one hand and cold water over the other long enough for both to adjust to the temperatures and then both hands are plunged into lukewarm water, the cold hand will feel warm and the hot, cold. It would seem that, in plunging the cold-adapted hand, nerve cells for perceiving cold are suddenly inhibited and those for perceiving heat are suddenly stimulated, while in the heat-adapted hand the reverse takes place.

Normally, the senses combine to produce a kind of common, unitary, or integrated perceptual experience. In dining, for example, the visual array on the table, the conversational tones or background music, and the tactile sensations, aromas, and taste of the food all combine to enhance the gustatory experience, with each sense contributing to it.

Physiologically, taste and smell appear to be particularly subject to intersensory effects interdependent. In other situations, seeing, hearing, touching, and often smelling and tasting are all employed in an intersensory way in object identification or location. Sometimes, however, the stimulation of one sense may activate an illusory sensation that is normally perceived by another sense, or a strong sensation may mask the perceptions of other senses.

Some musicians and others report that they see particular colours whenever they hear given tones and musical passages; poets sometimes claim to hear sounds or musical tones when they see words, images, and colours. Synesthesia may be induced with drugs, and, in rare psychiatric disorders, sufferers may not be able to tell whether they are seeing or hearing. Stimulation through one sense may enhance the function of another. Seeing a boat rocked by waves may activate the sense of balance in an observer on a pier to the point at which it causes seasickness.

A painting of an Arctic scene of frost and snow may evoke the sensation of cold or a shiver that produces gooseflesh. An explosion or gunshots may give a bystander the illusion of being struck. A picture of appetizing food may evoke sensations of taste and smell. Sensory rivalry, in which one stimulus inhibits the perception of another, may result from a conflict of cues if sensory information is ambiguous or discrepant, as in the tilted-room experiment discussed above , during which the visual sense conflicts with cues from the sense of equilibrium.

States of pain, panic, monotony, or fatigue may create conditions in which various senses mask or inhibit each other.

The Psychology of Visual Illusion (eBook)

A witness of a terrifying sight, for example, may become oblivious to all sounds. Distraction also can elevate the pain threshold, as in the case of wounded soldiers whose injuries become painful only after the stress of combat has subsided. Similarly, some dentists have used auditory analgesia a masking of pain by sound. Illusions called pseudohallucinations occur at times when feelings of anxiety or fear are projected on external objects, as when a child perceives threatening faces or monsters in shadows at night or sees goblins in trees.

A soldier tense with apprehension may in his fear perceive inanimate objects as an attacking enemy or one of his own comrades as the foe. In literature the character Don Quixote perceived windmills as enemy knights. Psychiatric patients have perceived people as machines, teddy bears, and devils. Emotions , compelling associations, and strong expectations frequently cause illusional misperceptions in everyday life. John may think Tom is Gary because he is hoping to see Gary or because he definitely wants to avoid Tom. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.

Visual Illusion

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Written By: Louis Jolyon West. See Article History. Read More on This Topic. In dramatic production the magical property with which a performing area is invested is augmented by the fictional action of the drama. Start Your Free Trial Today. Learn More in these related Britannica articles:. The stage becomes another locale by an act of imagination undertaken by both actors and audience.

The illusion of place…. Those effects generally become intensified with increased loss of sleep, but they also wax and wane in a cyclic fashion in line with hour fluctuations in EEG alpha-wave 8 to 12 hertz phenomena and with body temperature, becoming most acute in the….