I'll declare my interest straight out. I studied language and language acquisition as part of my degree, and the separate halves of the brain were always fascinating. When I was looking to get into sketching and painting some of the birds I saw I picked up a book called The New Drawing on the Right Side of the Brain by Betty Edwards. The concept is inspired: We have 2 halves of the brain and we know them to perform different functions. The left side is (usually) the logical, analytical side which deals with language; the right side has no linguistic capability but deals with more 'intuitive', parallel, spatial processing. We also know from experiment that the left, or linguistic, side tends to dominate, so when we try to draw we tend to use the left side, which is not properly suited to the task. This is why inexperienced drawers will draw a face by making eye shapes, and a nose shape, and generally constructing it from the little kit of shapes in their heads instead of drawing what they're looking at. I can vouch for this - faces drawn by me look much the same as they did when I was 7.
2 other important facts. The right side of your brain controls your left hand and vice versa. Also, in cases of severe epilepsy, a cure used to be severance of the Corpus Cerebellum, the large nerve cluster through which the two halves of the brain communicate. With that severed, the two halves continue to function perfectly normally but in complete isolation. People treated in this way have since been the subject of intense experimentation because, being as scientifically ethical as we are, we're unlikely to get others.
Having set the scene, what I mostly wanted to share was this extract from the book which made me laugh and think at the same time:
A few examples of the specially designed tests devised for use with the split-brain patients might illustrate the separate reality perceived by each hemisphere and the special modes of processing employed. In one test, two different pictures were flashed for an instant on a screen, with a split-brain patient's eyes fixed on a mid-point so that scanning both images was prevented. Each hemisphere, then, received different pictures. A picture of a spoon on the left side of the screen went to the right brain; a picture of a knife on the right side of the screen went to the verbal left brain. When questioned, the patient gave different responses. If asked to name what had been flashed on the screen, the confidently articulate left hemisphere caused the patient to say "knife." Then the patient was asked to reach behind a curtain with his left hand (right hemisphere) and pick out what had been flashed on the screen. The patient then picked out a spoon from a group of objects that included a spoon and a knife. If the experimenter asked the patient to identify what he held in his hand behind the curtain, the patient might look confused for a moment and then say, "A knife." The right hemisphere, knowing that the answer was wrong but not having sufficient words to correct the articulate left hemisphere, continued the dialogue by causing the patient to mutely shake his head. At that, the verbal left hemisphere wondered aloud, "Why am I shaking my head?"
In another test that demonstrated the right brain to be better at spacial problems, a male patient was given several wooden shapes to arrange to match a certain design. His attempts with his right hand (verbal left hemisphere) failed again and again. His left hand kept trying to help. The right hand would knock the left hand away; and finally the man had to sit on his left hand to keep it away from the puzzle. When the scientists finally suggested that he should use both hands, the spatially 'smart' left hand (right hemisphere) had to shove the spatially 'dumb' right hand away to keep it from interfering.
As I said at the start, the concept of the book is inspired; the idea that when drawing we want to reach a state where the usually dominant but spatially inadequate left brain is suppressed and the right brain takes over the processing. It's an almost trance-like state where perception of time disappears, and which most people will have experienced before (I get it when writing HTML/SQL, or driving long distances). I'm still only on the first few chapters and did my first exercises today which look awful, so I'm looking forward to comparing them with the results at the end of the book.