08: Eye's Right!
In the “Eye’s Right” chapter, a woman’s bizarre tendency to not ignore the left side of “the world” is discussed. Mrs. S, a woman in her sixties, experienced a stroke which impaired the deep/ back portions of her right cerebral hemisphere. The cerebral cortex is split into two hemispheres: right and left; these two sides exhibit “contralateral control” in which the left side of the brain controls the right side of your body and vice versa. When one side of the brain is damaged, the opposite side of the body is affected. For example, a stroke in the right hemisphere of the brain can leave the left arm and leg paralyzed.
In her case, because her “intelligence” wasn’t affected, she didn’t know she wasn’t seeing the “left side of the world;” she wasn’t aware of her wrong perception. As a result, items that were presented to her were invisible in that she didn’t see them because they were on her left side. Even when things were pointed out to her on the left side, it wouldn’t occur to her to tilt her head to the left. This further emphasizes the lack of existence of the left side of the world. With this came bizarre behaviors such as only putting makeup and fixing her hair on the right side only. In fact, when presented with a screen for her to visualize her left side, she freaked out due to invisibility of the left side.
The left and right hemispheres are connected by a group of white fibers called the corpus callosum. This structure allows for communication between the two hemispheres and allows for information from the left side to be carried out and processed on the right side and vice versa. When this part is impaired the communication between these two hemispheres is ceased. Patients that have this impairment are referred to as split brain patients in which the left and right sides act independently of each other.
Dr. Sperry, who did work on brain functions, presented an experiment that related to what Mrs. S experienced. A split brain patient was shown a toothbrush on the right side and identified is as a toothbrush. However, when the toothbrush was put on the left side he didn’t see anything at all. This is exactly what happened with Mrs. S. However, split brain patients could have both visual fields intact and identify both sides of the world, but don’t know how to put things together compared to Mrs. S who wasn’t aware of the left side world. Furthermore, because each half of the visual field projects to opposite sides of the brain, crossing at the optic chiasm, the left or right hemispheres could be observed.
We also have to take into consideration that each side of the brain has a certain dominance in terms of specific functions compared to the other side. In general, it is known that the right brain is dominant for spatial abilities, face recognition, visual imagery and music. With that being said, because her left side is paralyzed, we assume that the right hemisphere is impaired where visual imagery is dominant. However, she did come up with a strategy to see the left side: a rotating wheelchair. Now, if she cannot find something which she knows should be there, she can turn around in a circle until she finds what she knows is supposed to be there.
