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Axel Young
Axel Young


An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people.[1]


Illusions may occur with any of the human senses, but visual illusions (optical illusions) are the best-known and understood. The emphasis on visual illusions occurs because vision often dominates the other senses. For example, individuals watching a ventriloquist will perceive the voice is coming from the dummy since they are able to see the dummy mouth the words.[2]

Some illusions are based on general assumptions the brain makes during perception. These assumptions are made using organizational principles (e.g., Gestalt theory), an individual's capacity for depth perception and motion perception, and perceptual constancy. Other illusions occur because of biological sensory structures within the human body or conditions outside the body within one's physical environment.

The term illusion refers to a specific form of sensory distortion. Unlike a hallucination, which is a distortion in the absence of a stimulus, an illusion describes a misinterpretation of a true sensation. For example, hearing voices regardless of the environment would be a hallucination, whereas hearing voices in the sound of running water (or another auditory source) would be an illusion.

An auditory illusion is an illusion of hearing, the auditory equivalent of a visual illusion: the listener hears either sound which are not present in the stimulus, or "impossible" sounds. In short, audio illusions highlight areas where the human ear and brain, as organic, makeshift tools, differ from perfect audio receptors (for better or for worse). One example of an auditory illusion is a Shepard tone.

Examples of tactile illusions include phantom limb, the thermal grill illusion, the cutaneous rabbit illusion and a curious illusion that occurs when the crossed index and middle fingers are run along the bridge of the nose with one finger on each side, resulting in the perception of two separate noses. The brain areas activated during illusory tactile perception are similar to those activated during actual tactile stimulation.[6] Tactile illusions can also be elicited through haptic technology.[7] These "illusory" tactile objects can be used to create "virtual objects".[8]

A temporal illusion is a distortion in the perception of time, which occurs when the time interval between two or more events is very narrow (typically less than a second). In such cases, a person may momentarily perceive time as slowing down, stopping, speeding up, or running backward.

Illusions can occur with the other senses including those involved in food perception. Both sound[9] and touch[10] have been shown to modulate the perceived staleness and crispness of food products. It was also discovered that even if some portion of the taste receptor on the tongue became damaged that illusory taste could be produced by tactile stimulation.[11] Evidence of olfactory (smell) illusions occurred when positive or negative verbal labels were given prior to olfactory stimulation.[12] The McGurk effect shows that what we hear is influenced by what we see as we hear the person speaking; when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound.[13]

Some illusions occur as a result of an illness or a disorder. While these types of illusions are not shared with everyone, they are typical of each condition. For example, migraine sufferers often report fortification illusions.

The aim of this study was to evaluate the analgesic effect of transcranial direct current stimulation of the motor cortex and techniques of visual illusion, applied isolated or combined, in patients with neuropathic pain following spinal cord injury. In a sham controlled, double-blind, parallel group design, 39 patients were randomized into four groups receiving transcranial direct current stimulation with walking visual illusion or with control illusion and sham stimulation with visual illusion or with control illusion. For transcranial direct current stimulation, the anode was placed over the primary motor cortex. Each patient received ten treatment sessions during two consecutive weeks. Clinical assessment was performed before, after the last day of treatment, after 2 and 4 weeks follow-up and after 12 weeks. Clinical assessment included overall pain intensity perception, Neuropathic Pain Symptom Inventory and Brief Pain Inventory. The combination of transcranial direct current stimulation and visual illusion reduced the intensity of neuropathic pain significantly more than any of the single interventions. Patients receiving transcranial direct current stimulation and visual illusion experienced a significant improvement in all pain subtypes, while patients in the transcranial direct current stimulation group showed improvement in continuous and paroxysmal pain, and those in the visual illusion group improved only in continuous pain and dysaesthesias. At 12 weeks after treatment, the combined treatment group still presented significant improvement on the overall pain intensity perception, whereas no improvements were reported in the other three groups. Our results demonstrate that transcranial direct current stimulation and visual illusion can be effective in the management of neuropathic pain following spinal cord injury, with minimal side effects and with good tolerability.

Vision in the fovea, the center of the visual field, is much more accurate and detailed than vision in the periphery. This is not in line with the rich phenomenology of peripheral vision. Here, we investigated a visual illusion that shows that detailed peripheral visual experience is partially based on a reconstruction of reality. Participants fixated on the center of a visual display in which central stimuli differed from peripheral stimuli. Over time, participants perceived that the peripheral stimuli changed to match the central stimuli, so that the display seemed uniform. We showed that a wide range of visual features, including shape, orientation, motion, luminance, pattern, and identity, are susceptible to this uniformity illusion. We argue that the uniformity illusion is the result of a reconstruction of sparse visual information (from the periphery) based on more readily available detailed visual information (from the fovea), which gives rise to a rich, but illusory, experience of peripheral vision.

Why does the Moon look so big when it's rising or setting? The Moon illusion is the name for this trick our brains play on us. Photographs prove that the Moon is the same width near the horizon as when it's high in the sky, but that's not what we perceive with our eyes. Thus it's an illusion rooted in the way our brains process visual information. Even though we've been observing it for thousands of years, there's still not a satisfying scientific explanation for exactly why we see it.

But here's the thing: it's all in your head. Really. The Moon's seeming bigness is an actual illusion, rather than an effect of our atmosphere or some other physics. You can prove it for yourself in a variety of ways.

Photographers can simulate the Moon illusion by taking pictures of the Moon low on the horizon using a long lens, with buildings, mountains, or trees in the frame. So, remember when you see dazzling photos that feature a giant Moon above the landscape: those images are created by zooming in on distant objects near the ground. In other words, the Moon looks bigger in those photos because it's a zoomed-in view.

Brace yourself: we don't really know. Well, not really. Depending on your mindset, this news might be unsatisfying, or it could be a reason to marvel at our mysterious brains. But despite the fact that people have been observing this illusion for thousands of years, we still don't have a rock-solid scientific explanation for it.

There's also some thinking that objects in the foreground of your lunar view play a role. Perhaps trees, mountains, and buildings help to trick your brain into thinking the Moon is both closer and bigger than it is? There's an effect discovered a century ago called the Ponzo illusion that describes how this works. In the illusion, you have a scene where two lines are converging, like railroad tracks stretching away into the distance. On top of these lines are drawn two horizontal bars of equal length. Surprisingly, the horizontal bars appear to be different sizes, because your brain's hard-wired sense of how distance works forces you to perceive it this way. This effect is related to how forced perspective works in paintings.

A similar illusion was discovered in 1913 by Mario Ponzo, who drew two identical bars across a pair of converging lines, like the railroad tracks pictured left. The upper yellow bar looks wider because it spans a greater apparent distance between the rails. This is the "Ponzo Illusion."

A fun activity: Look at the moon directly and then through a narrow opening of some kind. For example, 'pinch' the moon between your thumb and forefinger or view it through a cardboard tube, which hides the foreground terrain. Can you make the optical illusion vanish?

mid-14c., "mockery, scorning, derision;" late 14c., "act of deception; deceptive appearance, apparition; delusion of the mind," from Old French illusion "a mocking, deceit, deception" (12c.), from Latin illusionem (nominative illusio) "a mocking, jesting, jeering; irony," from past-participle stem of illudere "mock at," literally "to play with," from assimilated form of in- "at, upon" (from PIE root *en "in") + ludere "to play" (see ludicrous). Sense of "deceptive appearance" first developed in Church Latin. Related: Illusioned "full of illusions" (1920).

While the main vision of DeFi's proponents is intermediation without centralised entities, we argue that some form of centralisation is inevitable. As such, there is a "decentralisation illusion". First and foremost, centralised governance is needed to take strategic and operational decisions. In addition, some features in DeFi, notably the consensus mechanism, favour a concentration of power. 041b061a72


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