The Mind's Eye

Like his book Musicophilia, Oliver Sacks' latest book The Mind's Eye is a collection of case studies concerning the brain. In this case Sacks discusses the brain's perception of visual data and how it relates to the rest of the brain.

One of the most striking phenomena is when the visual cortex is deprived of all input from the eyes in cases of blindness. The brain is flexible enough that the visual cortex can take over other perceptual functions, such as hearing or touch. But Sacks shows that the experience of the blind can take many different forms. In some they go into a "deep blindness", where they remember nothing of the visual world, colors, faces, shapes. Others still have a strong perception of the visual, including having a mental map of the world and an ability to visualize the faces of those they have never seen. This is one of the strongest sections of the book, reading about the different ways of perceiving the world. It is amazing and eye-opening to learn that some blind people can "see" their hands as they play the piano or do other things with their hands.

Another interesting phenomena is the condition of alexia, the loss of the ability to read. Some patients with alexia can see perfectly well and recognize individual letters, but cannot build the letters into words. Many can even write, but can't read what they have written. Others cannot even recognize letters or other familiar symbols. Some who have lost the ability to read also lose their spacial sense, so they easily get lost in their own neighborhoods or homes. It is fascinating to learn about the different connections in the brain and how they can go wrong. Sacks is great at explaining the basic workings of the parts of the brain and also shows how little we understand.

One of the longest sections describes his experience of losing most of his sight in one eye due to a tumor. He explains how in many patients the loss of vision in one eye can lead to a loss of recognition of things on that side of the body. If there is brain damage on one side of the visual cortex then one's whole perception of that space (the opposite side of the body) can go away. Some patients don't even recognize their own arms.

Another section talks about stereoscopy, the ability to see with depth perception. This is something that most of us take for granted until we lose it, as the author did when he had the tumor. But some people live without it and don't see what the big deal is. In the case he describes, a woman was able to achieve stereoscopy after living most of her life without it and was astounded with the results. She would be surprised to see a dinosaur's head coming at her in a museum or the many depths of the leaves of a tree.

Sacks has created another wonderful look at the brain with this book. He excels at describing experiences of people from their point of view, explaining what goes wrong in the brain, and how the brain is generally understood to work when it is working normally. There is a lot we can learn about the brain from these case studies where something stops working properly. The brain's processing of vision as presented here ties to our perception of the world around us and how we relate to it. Vision is related to our inner maps of the world, though our maps can be created and maintained with different sensory inputs like in the blind subjects. A-