How Do Optical Illusions Work?

How do optical illusions work?

The eyes and the brain have an interesting relationship. You would think that what we see is transferred to the brain and then the brain tells us exactly what our eyes transmitted. However, that is not the case.

For example, one type of optical illusion is the physiological illusion. This type of illusion includes afterimages. Afterimages are really not "there," but the brain perceives them as being real because the brain was over stimulated by, in this case, bright colors.

The brain also uses information learned in the past to help it perceive the images that the eyes send. The brain loves familiarity and dislikes "seeing" things that are out of the norm. Therefore, the brain can have a tendency to "force" an image into something that the image is not, just so the image looks more familiar. These are called cognitive illusions.

There are several types of cognitive illusions, including distorting, paradox and ambiguous illusions. Distorting illusions, the most common type, can also have a physiological basis. These types of illusions take advantage of our perceptions of size, length or curves. Paradox illusions are physically impossible, but there they are real. If you have ever looked at M. C. Escher's work, you know what paradox illusions look like. Ambiguous illusions offer more than one image to consider, annoying the brain because it can't focus on a single picture.

Some famous optical illusions to take a peek at include:

The Necker Cube, by Louis Albert Necker. First published in 1832, the Necker Cube is an example of an ambiguous illusion.

The Mueller-Lyer Illusion, a distorting illusion

The Penrose Stair, a paradox illusion

Interestingly, nature also conspires to confuse us. For example, a mirage is a naturally occurring optical illusion.

The bottom line is that an optical illusion isn't "real," although the brain interprets the illusion as being true.