illusions- eyes supplement

December 2, 2009

Necker Cube

The Necker Cube is an ambiguous line drawing. It is a wire-frame drawing of a cube in oblique perspective, which means that parallel edges of the cube are drawn as parallel lines in the picture. When two lines cross, the picture does not show which is in front and which is behind. This makes the picture ambiguous; it can be interpreted two different ways. When a person stares at the picture, it will often seem to flip back and forth between the two valid interpretations.

Kanizsa triangle

The kanizsa triangle is an optical illusion  first described by the Italian psychologist Gaetano Kanizsa  in 1955. In the accompanying figure a white equilateral triangle is perceived, but in fact none is drawn. This effect is known as a subjective or illusory contour. Also, the nonexistent white triangle appears to be brighter than the surrounding area, but in fact it has the same brightness as the background.

McCollough effect

The McCollough effect is a phenomenon of human visual perception in which colorless gratings appear colored depending on ( contingent on) the orientation of the gratings. It is an aftereffect requiring a period of induction to produce it. For example, if someone alternately looks at a red horizontal grating and a green vertical grating for a few minutes, a black-and-white horizontal grating will then look greenish and a black-and-white vertical grating will then look pinkish. The effect was discovered by Celeste McCollough in 1965.

The Chubb illusion

The  Chubb illusion is an optical illusion wherein the apparent contrast of an object varies dramatically, depending on the context of the presentation. Low-contrast texture surrounded by a uniform field appears to have higher contrast than when it is surrounded by high-contrast texture. This was observed and documented by Charles Chubb and colleagues in 1989.

Grid illusion

grid illusion is any kind of grid that deceives a person’s vision. The two most common types of grid illusions are  Hermann Grid illusion and the Scintillating grid illusions.

Why do we see Illusions ?

The Human brain put images together because they have learned to expect things, and sometimes the data might get a little confused.

We may see an illusion because we know what we are expected to see, even though part of a picture or design may not be completely there. The basis of this is in how we perceive things.

That almost explains everything right there. If our brain and eyes did not function like they do, we would not see illusions like we do.

One example of optical illusion is the television. The television is just shows us a continuous flow of still pictures, one right after the other. Our eyes along with your brain fill in all of the empty spots. Our brain has learned to expect movement. As a result, our brain can fill in all of the missing pieces and the television appears to be actually moving to you, even though it really isn’t!

A computer monitor is also one big optical illusion. Sometime when you have a chance, look at a computer screen really close for a minute or two. You will notice that you computer screen is made up of tiny red, green, and blue dots. The illusion is, you see more than just red, green, and blue dots; you see thousands of different colors. Our brains put the red, green, and blue dots together to make the colors.

Optical illusions just trick you into seeing something else. They are an error in our perception of the illusion.


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