Optical Illusion and How They Work

Optical Illusion: Your eyes are incredible structures. Did you know that if you have blue eyes, you and every other person with blue eyes on the planet share a common forefather? This is due to the mutated gene that gave rise to blue eyes more than 6,000 years ago. Brown eyes were the primordial colour for humans.

You can learn how your eyes function by going much further than the intriguing tales they tell. You see the world the way you do because your eyes and brain constantly communicate with one another.

For instance, the layer in your eyes called the retina, which is responsible for creating visual images, actually “sees” images that are reversed and upside down. Your brain turns the images around so that you see them inverted and backward. Each and every time. Yes, your brain is the original Photoshop genius.

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Types of Optical Illusion

Physiological illusions, cognitive illusions, and literal illusions are the three basic categories of optical deception. There is a common thread among all three sorts of illusions. The perception of the image that is presented to the brain is inaccurate. For this reason, optical illusions are referred to as an “eye trick.”

Lateral Optical Illusion: A literal illusion is when the image you see is different from the images that make it up. For example, the illustration Hill created which is actually two images strategically drawn to look like one fluid image is a literal illusion. Think of it as a reversible figure. The end result you see in a literal illusion is based on your perception.

Physiological Optical Illusions: Because they capitalise on the excitability of the brain’s senses, these kinds of visual illusions are more complicated. The brain is confused by the amount of light, motion, colour, depth, and size that the eye “sees.”

Physiological optical illusions give you the ability to view mind-bending things like impossible images and geometric illusions. Multiple figures initially appear to be three-dimensional.

That’s because the brain interprets it that way right away. Following further investigation, the brain realises what the eye is seeing. Nature does not have the image in question.

Cognitive Optical Illusions: Scientists and psychologists are most interested in this type of illusion because it is the most complex type of trick the eye can play on the brain.

Unlike other optical illusions, these rely on the unconscious level mind’s thoughts and how it connects one object to another.

In other words, what you see is thought to reveal the depths of your thinking. A cognitive optical illusion reveals your brain’s inferences and understandings about something that has not been explained.

Hering Illusion

The Hering illusion is a geometrical-optical illusion that was unearthed in 1861 by German physiologist Ewald Hering. When two straight and parallel lines are placed in front of a radial background (such as bicycle spokes), the lines appear to be nodded forwards.

There are numerous explanations for why the radiating pattern causes perceptual distortion. Hering attributed the illusion to an overestimation of an angle made at the points of an intersection.

If correct, it’s interesting that what yields is the straightness of parallel lines rather than emanating lines, implying that there is a hierarchical ordering among illusion elements.

Others have suggested that angle overestimation results from lateral inhibition in the visual cortex, while others have suggested a bias inherent in extrapolating 3D angle information from 2D projections.

Simultaneous Contrast Illusion

The horizontal bar in the preceding image appears to be graduated, moving from light grey to dark grey in the opposite direction as the background. If you cover everything except the bar, you’ll notice that it’s black and white. There is only one solid-coloured bar.

The checker shadow illusion is similar to the “simultaneous contrast illusion.” The brain interprets two ends of the bar as having different lighting and deduces what the bar’s true shading is (if it were lit evenly along its length). 

It thinks that the left end of the bar is a light grey object in dim lighting. The right end looks like a darker object that is well-lit.

Cafe wall illusion

The café wall illusion is a geometrical-optical illusion in which the parallel straight dividing lines between staggered rows of black and white “bricks” appear to be sloped.

Each “brick” is surrounded by a layer of “mortar” that is transitional in colour between the dark and light “bricks.”

The illusion was largely attributed to illumination, the light spreading from dark to bright zones in the retinal image, in the first successful attempt at its reinterpretation, and indeed the image disappears when black and white are replaced by different colours of the same luminance (isoluminant).

But a component of the illusions remains even when all optical and retinal components are factored out. Contrast polarities seem to be the determining factor in the tilt’s direction.

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