THE THEME FOR VlSlON AWARENESS WEEK WAS SELECTED BY THE CANADlAN ASSOCIATlON OF OPTOMETRISTS TO REMIND EVERYONE THAT MAINTAINING GOOD VlSlON REQUIRES NO SPEClAL MAGlC. SlMPLY A REGULAR EYE EXAMINATION. (YOUR OPTOMETRlST WILL TELL YOU WHAT "REGULAR" MEANS FOR YOU.)

 

MEANWHILE, DON'T FEEL BAD IF YOU'RE TRICKED BY THESE OPTlCAL ILLUSIONS. AS THE FOLLOWlNG EXPLANATlONS REVEAL, THE BRAlN DOESN'T ALWAYS PUT THE CORRECT lNTERPRETATlON ON THE lMAGES IT RECEIVES FROM YOUR EYES --- NO MATTER HOW GOOD YOUR VISION!

 

 

Why do these figures seem to be different in height?

They are identical.

The brain determines "perception" not only from what the eyes actually see. It adds interpretation from clues offered by a particular object's surroundings. But the brain's interpretation is not always right and this figure is a perfect example of such distorted reality.

 

From birth, we encounter examples of seeing things that are the same size -- like a line of hydro towers -- which seem to become smaller the farther away they are. This illustration provides a very powerful visual suggestion that the figures are moving into the distance, a perception that is created by the "leading lines" which come to a point at the right side of the image.

 

Our brain tries to tell us, therefore, that the figure on the right is "farthest" from us, in spite of the fact we know this cannot logically be true on a two-dimensional surface like a sheet of paper. So even though the figure is actually the same size as the other two figures (measure them, our brain is overpowered by the false "distance" clues in the picture, and decides wrongly that the figure on the right must be bigger than the other two.

 

Why do you see three arms?
Then four?
Then three again?

This is an example of an impossible figure. Even though our brain seems at first to tell us the figure is quite normal, we quickly realize that if we tried to construct it, say from lumber, it could not be brought into existence.

 

If we look at what seems to be the face closest to us, we see what appears to be a three-dimensional "E", that is, a figure with three arms. But when we shift our gaze deeper into the object, particularly along the right edge, we find there now appear to be four arms to the same structure.

 

The image is not so much an "illusion" as it is an example of tricking the brain with cleverly placed lines. This type of impossible figure was extensively used by Dutch artist MC Escher to create elaborate, but impossible staircases, waterfalls and various other structures in his art. Your public library undoubtedly has one or more published collections of Escher's work, many of which have also been reproduced as art posters.

 

When you stare at the wheel,

why do you see spokes?

There are none.

 

This an example of apparent movement. You may see ghostly "spokes" in the wheel and, to add to the confusion, these spokes may even refuse to stand still 

The illusion is even more pronounced when you hold a copy of the illustration and move it in small circles. The figure actually appears to rotate in the direction in which you are making the circular motion.

 

The eyes are the "front entrances" to a person's visual system, but your eyes are not perfect and what they see is subject to the brain's interpretation. The harder you concentrate, the more your eyes tire of the exercise. They flick around from point to point on the image and, as they do so -- even though you might not realize it they create a conflicting pattern of images and after-images. The resulting image confusion can seem to create "spokes" or "airplane propellers" in the concentric lines, an illusion called "moiré" that was first reported in 1876.

 

Why do the long,
dark lines seem to bend?

They are straight.

It is really very easy for our eyes to "trick" our brain. An example we encounter probably most often is at the movie theatre. What we think is a motion picture is nothing more than a series of still pictures flung so quickly at the eyes that the brain cannot keep up with all the visual input. So, rather than see the images as a series of still pictures, our brain takes the lazy way out, jumbles the film images together almost, but not exactly as fast as they appear, and we "see" motion.

 

This image shows another way the brain can be tricked. By changing the surroundings of an image, we can change what we seem to see. On a piece of white paper, two straight, parallel lines are clearly seen as two straight, parallel lines. But if we overlap them with another series of lines which seem to expand outwards from a single point, then our brain believes it perceives a similar expansion, or bulge, where those radiating lines cross the first two straight, parallel lines.

 

This figure is called the Hering Illusion after its discoverer in 1861.

 

Why do the two centre squares seem to be different in size?

They are exactly the same.

 

Our brain's ability to judge the size of an object that our eyes see is very much affected by that object's surroundings. By taking two objects the same size (the centre squares) and putting them in very different sized surroundings, the brain makes false judgments concerning the original objects.

 

In this figure, a square appears smaller and more compact when its surroundings are large and imposing. But when the size of the surrounding objects is reduced, the centre square appears to have grown and, even though it is the same size, it seems noticeably larger than its more heavily surrounded counterpart.

 

The illusion is a variation of the Delboeuf Illusion, first discussed in 1892.

 

 

James Cielen is an outstanding illusionist. At the 60th annual convention of the International Brotherhood of Magicians in Boston, MA, he was selected to receive the distinguished Gold Medal of Excellence, only the third magician in history judged worthy of this honour. James Cielen travels the world; formerly from Winnipeg, his home is now in Las Vegas.