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Optical Illusions

Your Eyes Playing Tricks!

What Are Optical Illusions?

Optical illusions are an interesting phenomenon that involves a shifting of perception. Often an image is seen that does not exist or exists in a different manner than it initially appeared. These changeable images are due to the way the human eye interprets size, shape, distance, linear lines, and so forth.

The information that is gathered by the eye will be processed by the brain. This gives rise to a specific perception of what is viewed. Sometimes the perception and the reality are two separate entities. These perception mistakes come in three illusory types primarily.

These types are: cognitive illusions where an image in view is inferred though it does not actually exist, physiological ones which affect the eyes and brain via excessive amounts of specific stimulation such as lighting and color, and Literal optical illusions which are images created by way of the objects that make them.

Examples of Cognitive Illusions

The Necker Cube is one of the most commonly cited cognitive illusions around. This simplistic design is basically a wire frame box that shifts the angle and direction of the cube’s point of view in reference to the viewer’s vision. It draws on the human eye’s ability to perceive two dimensional objects in a three dimensional manner.

This capacity is used to turn simple lines into a completely rendered box. Depending on where the viewer focuses their vision it can be seen from a downward position or an upward point position.


Another cognitive illusion that is based on the concept of the Necker Cube is the Impossible Cube. The Impossible Cube is designed similarly to the Necker Cubeexcept that it appears to be made of solid beams. This particular optical illusion is not completely solid like the original derivation it was born of. When it is drawn, or otherwise rendered, an impossible cube has two missing sections in the front.

These missing sections allow for human perceptions to misinterpret what is actually being seen so that a solid three dimensional box with variable angles can be viewed.


Beyond the simplicity of the Necker and Impossible Cubes there are many cognitive illusions throughout the world. One of the most famous is the Cafe wall illusion found on a local cafe at the bottom of St. Michael’s Hill in Bristol. This illusion is comprised of perfectly horizontal lines combines with staggered black and white bricks.

To make the illusion work each brick must be mortared with a gray mortar that comes close to being a perfect intermediary of the two colours. The end result is that the perfectly parallel lines look as though they are curving or bent.


Examples of Physiological Illusions

A prime example of a physiological illusion that is crafted by the hand of man, as opposed to the natural ones seen when afterimages occur due to over-stimulation from bright light and similar occurrences, is the Hermann grid illusion. The Herman grid illusion, first reported by Ludimar Hermann in 1870, is a series of white intersections around black squares.

The contrast between the two images causes the human eye to see gray blobs in the centre unless an specific intersection is focused on.


Similar to the Hermann grid illusion is the scintillating grid illusion. While fundamentally created in the same way this particular illusion trades in the white intersecting lines for gray ones. At each intersection there is a superimposed white dot. When the grid is viewed, black dots will appear inside the white ones in a dynamic manner.

Just like the Hermann grid illusion, however, if a particular intersection is gazed upon then the black dot will not appear within said intersection.


Another equally interesting example of physiologically based optical illusions is via a natural or contrived phenomenon known as mach bands. Named after Ernst Mach these bands are the creation of the human eye when viewing two different uniform shades on the same surface.

A region that is uniformly white connected with one that is uniformly white will cause this when an intermediary colour strip is placed through the center of the connecting location. The illusion is that at either side of the center strip a lighter band of colour will appear while on the darker side a darker band will appear.

This can appear in many natural locations and also plays havoc in dental radiology if the dental practitioner does not take them into account when diagnosing a problem while viewing the grayscale images taken of the mouth.


Examples of Literal Optical illusions

Literal optical illusions are caused by the interaction of one or more objects. One of the most well known types of illusion in this category is the “gravity road” or “Magnetic hill”. While some would have it seem that places like this are supernatural or paranormal the truth is that when viewing such a location a very gentle downward slope appears to be an upward one due to a lack of horizon in view.

This means that something as simple as a ball or rolling car might appear to move uphill against the force of gravity. It is actually rolling downhill in reality.

Less spectacular in scope but equally interesting versions of literal optical illusions include the strange ability of the eye to fill in details that do not naturally exist. The eye and brain connection to perfect perception will often pick and choose specific objects in view to focus on.

This is the primary method through with a literal optical illusion works. One topographical illusion that is quite interesting involves an elephant with more than four feet.


Another interesting literal optical illusion is world famous. The interplay of light and shadow mixed with natural terrain formed together to insight wild speculation and rumour for quite some time. The rumour was that there was possible intelligent life at one time on the planet Mars due to what appeared to be a carved face on its surface.

Later satellite surveillance and other information would disprove this as simply a trick of the light.

For more information on this phenomenon visit the NASA web site.


After Thoughts

The capacity for the human mind in accordance with the physical capacity of the eye often leads to interesting, sometimes dangerous, other-times hilarious visual imagery that does not exist objectively but seems to be real subjectively.

These optical illusions are perfectly normal parts of the human experience and are not caused by malfunctioning eyes or brain damage normally. The ability to interpret patterns in bizarre ways is not only entirely natural it can be quite entertaining as well.

In the end these “tricks of the light” as some call them, are normal and commonplace for individuals that actually take the time to truly look at the world around them.

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