Optical Illusion

Optical illusions prove human senses are fallible, that what you see does not always correspond to reality. People tend to think of optical illusions as tricks in books, but they actually effect nearly every part of modern life as the eye's capacity to be manipulated is what makes all print and visual media possible. Learning some facts about optical illusions is to learn essen
tial information for understanding the information age.

History

In the ancient world, people didn't know if optical illusions were the "fault" of the eyes or the mind. The first recorded theorizers on optical illusions were the Greek thinkers Epicharmus and Protagorus in 450 BCE. Epicharmus implicated the body whereas Protagorus implicated the mind. One hundred years later, Aristotle came up with a view balancing these extremes. In the twentieth century, artists began experimenting with illusions, in a movement known as optical art or "op art." By challenging the viewer to make sense of all sides of the illusion, op art made its audience participants in the artwork.

How Optical Illusions Work

Optical illusions occur when what the eyes see conflicts with what the brain expects. For example, if a series of concentric unconnected curved lines appears like a spiral, it is because the brain is so accustomed to perceiving such figures as spirals that it takes work to realize the drawing is, in fact, not a continuous spiral. Similarly, the "infinite staircase" illusion is possible, in part, because the brain is so used to the length of a drawing representing three-dimensional height.

Dithering

Nearly all forms of media are optical illusions. Print in books and newspapers is not made up of solid letters, but are in fact dots of black, red, yellow and blue ink placed so closely together the mind perceives them as solid. Television screens work in a similar way -- images on screen are not always the colors they appear to be but are in fact tiny dots of red, blue and green light projected so closely together that they are perceived as all different colors. This illusion of making a full-color image from only primary colors is called dithering.

Movies and Colorblindness

Movies are possible because of principle called "persistence of vision," the principle that images remain on the eye for 1/17 of a second, meaning images flashed faster than that (most movies are shot at 24 frames per second) cannot be perceived as separate images, creating the illusion of moving images. Common colorblindness tests are types of optical illusions. Everyone sees the same image, but a normal sighted person perceives the pattern of dots in a circle as one number, and colorblind people will perceive different numbers depending on their type of colorblindness.