Illusions: Why You See What You Do

Optical Illusions: Why You See What You See

A popular dictum states, "seeing is believing". Most people understand that to be true enough, most of the time - but there are exceptions to this rule, as with most rules. From the simplest drawings to complex photographs and artwork and even in reality, optical illusions have always been around. Through out this paper you will be given examples of optical illusions, and learn why it is you see them.

The first illusion is known as the Muller-Lyer illusion. This illusion was discovered in 1888 and is quite famous (Komorotskaya). The picture below is an example of this illusion:

In this case the question is: are the two horizontal lines equal in length. The correct answer for this would be "yes." You can double check by measuring each side with a ruler. The reason most people would think that the top is slightly bigger, is because our brain makes mistakes about the relative depths of the two lines. We are used to seeing outside corners of buildings with lines sloping inward, away from them. In these situations, the brain knows that the line running down the outside corner is the closest part of the image to us. The brain realizes that this line is really shorter than it appears when compared to the rest of the building (Muller-Lyer). We are also used to seeing the inside corners of rooms with the lines of the roof and floor sloping outward away from them. In these situations, the brain knows that the corner is the furthest part of the image from us. The brain realizes that this line is really longer than it appears when compared to the rest of the room (Muller-Lyer). When the brain compares lines from these two situations to each other, it reduces the size of the line with the inward sloping tails (the corner of the building) because it thinks this line is closer to us. It increases the size of the line with the outward sloping tails (the corner of the room) because it thinks this line is further away. This makes the line with the outward facing tails look longer (Komorotskaya).

The second illusion is one that was found by Johann Zollner in 1860 (Gibilsco, 21). This is another well-known illusion. The picture below is an example of Zollner's illusion:

In this illusion the long diagonal lines, although seem crooked, are perfectly parallel with one another. The Kollner Illusion is pretty easy to explain. In this illusion, the brain tries to increase the angle between the