04: The Zombie in the Brain

The Zombie in the Brain is about a neurophychologist named David Milner who ran experiments on a girl named Diane Fletcher. Diane had moved into a new house, and while taking a shower, lost conscience because of a carbon monoxide leak. She awoke after being saved by her husband only to be blind. After a few days she noticed she was able to distinguish colors and textures but was still blind. Intrigued by this, Milner ran an experiment where he held up a pencil and asked Diane to identify it. Although she was unable to tell him what it was she was able to swipe it out of his hand to feel it. The next experiment was with an envelope and a slit. Though she could not see the slit at all, she was able to put an envelope through it with ease.

These experiments prove that vision is a very complicated process which is controlled by many different variables. Milner says that we would be able to understand more by being able to read nerve impulses, which code for one’s vision. He then uses a few optical illusions to show that the brain recognizes patterns in the same way you use words and letters to describe things in your everyday life. He uses the patterns on a peacock tail as an example. Due to the lighting of the sun, the spots seem to protrude from the tail feathers making them even more noticeable.

Milner says that there about 30 different known areas of the brain that interpret vision. One part controls motion vision (MT) and one controls color blindness (V4). The other 28 serve unknown purposes. While Diane's case is unusual, there can be many ways to distort vision.

We are then given a simple visual pathway for signals from the retina. The signals start in the retina, travel to the optic nerve, travel to the optic chiasm, and split to make their ways to the superior colliculus and the lateral geniculate nucleus. He also mentions a patient who was missing his primary visual cortex. Though he was not able to see on his left side, he was able to distinguish dots of light to perfect accuracy. He believe this happened because the signal gets transmitted to the superior colliculus to the parietal lobes, which are guiding his hands. He labeled this sensation “blindsight.”