Three Brain Mysteries

Why do we see optical illusions?
What causes amnesia?
Why is our handwriting unique?

Why do we see optical illusions?
Optical illusions occur because our brain is too good at interpreting what it sees. We live in a three-dimensional world (up-down, right-left, backwards-forwards). We are accustomed to viewing the depth cues of this three-dimensional world. When presented with a two-dimensional drawing, the brain tries to reinterpret the flat image as if it were three-dimensional. "The brain is not built to look at pictures, that's the basis for many illusions," claims Dr. Rudier von der Heydt, a physiologist at Johns Hopkins University in Baltimore.

In the famous Ponzo Illusion, the top horizontal line appears longer than the bottom line, even though they're really the same length. This is so because the brain is accustomed to observing in real life that the parallel sides of a road appear to converge as the road disappears into the distance. Because the brain is used to reading perspective cues this way, it concludes that the horizontal line in the top part of the Ponzo illusion---where the vertical lines almost converge---is more distant than the line in the bottom part of the picture. But since the "more distant" line doesn't appear smaller than the "nearer" line, the brain mistakenly concludes that it must have been larger in the first place.

In the equally famous Vase-Face Illusion, again the brain thinks in 3-D. In the everyday world, our visual surroundings consist of objects set in front of other objects or backgrounds. The brain gets used to this and "looks" for an object in the foreground and an object for the background. In the Vase-Face Illusion, it "sees" a vase if it chooses white for the foreground and black for the background. It "sees" two faces if it chooses black for the foreground and white for the background. We can control the process by flip-floppying back and forth between the two images as we wish.

The Kanizsa Triangle, also a famous illusion, shows that even looking for the outlines of objects can fool the brain. In trying to distinguish an object from its surroundings, the brain always "looks" for the object's contours. This is so even when the object is the same colour as its background or when its edges are partially hidden by something in front of it. This ability to infer objects and contours when they don't exist deludes you into seeing two triangles and three circles.

Studies show that you can't refuse to experience an optical illusion. The ability to interpret depth cues or complete broken contours is simply too important to perception to be turned on and off at will. Dr. von der Heydt has found evidence that seeking out contours is hardwired into our brain cells. Other studies show that even infants have some sense of depth, edges, and when something is partially hidden.

"The brain is always striving for a three-dimensional interpretation", claims Dr. von der Heydt.

What causes amnesia?
Functional amnesia (FA), the condition in which a person blanks out the past, but is still able to form new memories is extremely rare. Brain specialists contend that this kind of memory loss is much more likely to result from an extremely stressful experience, rather than from an injury.

The current thinking among brain scientists is that memories are storied throughout the brain and not in a single memory centre. This means that it's unlikely that a single physical injury could wipe out all old memories. The brain is not so stupid as to put all of its memory eggs into one basket so to speak---just in case the basket gets overturned.

Neurological amnesia (NA), a more common type of amnesia, does result from brain injury. Victims of NA are more likely to have trouble forming new memories, rather than recalling old ones, either temporarily or permanently. The brain's temporal lobes, located at the sides of the head just above the ears, contain areas crucial to much memory storage. If you disrupt the temporal lobes, there's a strong likelihood you'll be left with a memory gap.

A mild concussion that doesn't cause permanent damage may still leave the brain unable to retain the memory of what led up to the injury or to recall the first few hours or days of recovery. This frequently happens to rugby players, boxers, and other athletes in high contact sports. A more severe blow could erase slightly older memories and interfere with new memory formation for a longer time. Still more serious trauma may completely destroy the ability to retain anything that happens after the injury.

The brain can only take so much.

Why is our handwriting unique?
Handwriting is an extraordinarily complex brain activity. Think of all the elements involved. For starters, the brain must determine what you think the written letters should look like, how you should hold your pen, how fast or slow you should write, how the nerves carrying the brain's instructions to the muscles innervate muscle fibers, and so on. Any change anywhere along this path will alter your handwriting. The system is really complex. No two people have the same brain, anatomy, muscle-nerve relationship, or mental image of letters.

Of course, it's possible to copy another person's writing. But it takes great skill and practice. And even if you trace someone's handwriting, you can't precisely duplicate the angle, pressure, or speed of the pen strokes of someone else. What's surprising is not so much that handwriting is unique, but that the handwriting of any two humans is even similar.

Your handwriting is as individual to you as your fingerprints.