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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. 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. In addition, Gestalt theory can be used to explain the illusory contours in the Kanizsa's Triangle.

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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. 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. Our brain makes sense of shapes and symbols putting them together like a jigsaw puzzle, formulating that which isn't there to that which is believable. The Gestalt principles of perception govern the way we group different objects. 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.

Rotating Rings

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. 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.

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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 M. 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.

Visual Phenomena & Optical Illusions

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.

Perceptual constancies are sources of illusions.

Optical 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 compared to 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.

21 Optical Illusions That Prove Your Brain Sucks

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. 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 [22] is an example of an illusion based on distortions in shape constancy. 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.

Cypress Hill - Illusions

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. 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.

The "can't un-see" feeling that many people have when looking at illusions is a perfect example of the brain doing more than just translating what our eyes see. And optical illusions are not just a function of our eyes and brains; our perception may also largely be influenced by cultural factors. While the biological basis for how optical illusions might work is universal across humans, when some illusions are shown to people in different cultures, not everyone saw the same thing or missed the same visual cues [sources: Schultz , Alter ].

In a study, most European South Africans thought the lines were of different lengths but bushmen in some South African tribes correctly noted they were the same lengths. Scientists have theorized that people in western societies are used to seeing straight lines and geometric shapes, and people with other cultural experiences aren't exposed to the same geometric configurations, so their brains don't leap to the same conclusions when exposed to illusions that are built upon geometric trickery [source: Schultz ].

However, when test computers designed to mimic the brain's activities were given the same illusion, they are also duped. So the cultural influence on perception of illusions, if it actually exists, is still a big question [source: Schultz ]. Most of the optical illusions we are used to seeing, such as the "devil's tuning fork", have been around for a long time. The solution to this apparent mystery is contained within the replies to the initial Tweet, but we'll let you enjoy it in the meantime. This illusion requires you to stare at the white dot on the woman's nose on the left for 15 seconds, then look to the right of the image at the blank space.

You should see a flicker of the full colour photo of the woman. You would be forgiven for thinking this image is just a really bad Photoshopping, but it isn't. The difference in air temperature acts as a lens - refracting light and distorting images as we see them. This photo appeared on Imgur and caused a bit of a splash. A little girl appears to be jumping into a swimming pool while simultaneously blowing bubbles like she's already underneath the surface.

Commenters quickly pointed out that her hair is dry and the apparent air bubbles could just be droplets of water from the splashing, but no conclusion was reached as to what was actually happening. This simple illusion is created by having a reflection of a nearby lamp showing in the lenses of a pair of spectacles. The resulting photo seems to show eyeballs staring back at the viewer from the glass.

What animal do you see? (Hint: there are two right answers.)

This one is a simple trick of the eye. This is not an animated picture, it's a static file that shows a mass of intertwined snakes. But if you stare at different sections you'll see the snakes writhing and squirming. Another classic deception. This image is not animated, it's just a simple JPG, but if you're reading this text then you're probably seeing it spin out of the periphery of your vision.

This optical illusion has taken on many different forms since it first found its way into publication in a book "Philosophical Investigations" by Ludwig Wittgenstein in Here it is suggested that there are ambiguous images that can be seen in two or more different ways. In this instance, the drawing could be a rabbit or a duck or both and what you see first will be down to your perception of the world or based solely on suggestion - the duck and rabbit axis in this version make it easier to quickly decipher both variations.

This photograph taken on the beach seems to show the speaker on a floating platform. No doubt down to our brain interpreting the shadow of the flag blowing in the wind as the shadow of the speaker's platform and microphone instead. There are a few of these sorts of optical illusions on the web — a simple image of two people embracing throws your brain into confusion where the couple are at strange angles and it's hard to immediately decipher which head or other body part belongs to which person.

Here Stuart Rutherford managed to magic an owl's face inside his coffee mug by simply dropping a couple of Hula Hoops into the mix. Who'd a thunk dunking a couple of Hula Hoops in your coffee would be so beautiful pic. One of the finalists for the " Best Illusion of the Year Contest " makes for pretty mind-bending viewing. Here Kokichi Sugihara places a set of cylinders in front of a mirror. The reflection shows a different shape until the object is revolved and then we see the opposite.

It's best viewed in the video below. If you're left scratching your head after watching that video, you can see a breakdown of how it works here:. Last year Blake Lively posted an image to her Instagram account showing a Magic Eye-like image to help promote her shark movie "The Shallows". If you're struggling, the official Magic Eye website has instructions on how to view the 3D images but basically you're trying to focus through the image while looking at it or blurring your vision until it becomes clear.

Erik Johansson is a Swedish photographer and a whizz with Photoshop who likes to take real photographs and turn them into surreal optical illusions. Common sense crossing is just one of his many works and one that we find particularly messes with our eyes! At first glance, you'd be forgiven for thinking that this helicopter was using some sort of new military stealth technology to take off without spinning its propellers.

In fact, it's just an illusion created by matching the video camera's shutter speed to the rotation speed of the rotors. Magnificent artist Howard Lee creates hyper-realistic drawings that are so brilliant it's hard to tell them from the real thing. This talent for creating optical illusions is demonstrated in his Youtube video which shows him cutting, bashing and setting fire to the real versions of his creations.