Chapter 1. The Split Brain: Lessons on Language, Vision, and Free Will
1.1 The Split Brain: Lessons on Language, Vision, and Free Will
Short Description
Twenty years ago Joe underwent surgery that split his brain. Surgeons severed the corpus callosum, the bundle of fibers connecting the two hemispheres.
Long Description
As a result, information no longer travels from one side of Joe’s brain to the other. He became an important participant in neuroscientist Michael Gazzaniga’s continuing study of hemispheric differences. The video suggests that studying split brain patients such as Joe could provide valuable insight into the source of the illusion of conscious free will.
Gazzaniga tests the linguistic abilities of the right and left hemispheres of Joe’s brain. Words presented on the right side of Joe’s visual field go to his left hemisphere and he calls them out easily. Words flashed on the left side of his visual field go to his right hemisphere and Joe says he sees nothing. Nonetheless, he draws a picture of the word that was presented. Because speech comes from the left hemisphere, Gazzaniga also believes that the left hemisphere may be dominant in generating consciousness.
Joe reports that he feels unchanged by his surgery. If the conscious feeling of self-identity comes from both hemispheres Joe would likely feel quite different. Thus, Gazzaniga’s bold conclusion is that Joe’s inner voice must come from only one side of his brain. Since our inner thoughts are all in words, that voice must come from the left linguistic side.
In another experiment, Joe sees two words simultaneously. After seeing the word “hour” in his left visual field and “glass” in his right visual field, Joe draws the picture of an hourglass. With his left hemisphere, he names the hourglass immediately. However, when asked, he reports only having seen the word glass. When asked why he drew an hourglass, he invents an explanation. Joe seems to have been fooled by his own left hemisphere.
Gazzaniga notes that this tendency to offer after-the-fact explanations for behavior is not unique to split brain patients. Rather, it is what we all do as we seek to understand and explain the automatic nature of many of our own behaviors.