Split Brains and Self-Deception

I recently attended a presentation of the Center for the Explanation of Consciousness at Stanford University. The speaker was Michael Gazzaniga, who directs the University of California at Santa Barbara’s SAGE Center for the Study of the Mind. For decades I have been citing Michael’s fascinating work with split-brain patients. He discusses these cases and many other professional and personal adventures in his new book, Tales from Both Sides of the Brain: A Life in Neuroscience. See:


The two hemispheres of the brain are connected by an array of nerve fibers called the corpus callosum. Some people have a form of epilepsy that can best be relieved by severing this link. After the surgery, the two hemispheres no longer communicate with each other through this informational bridge. Remarkably, these patients notice little change in their own conscious experiences and it is quite difficult to detect behavioral changes. But Gazzaniga and others have designed clever experiments showing that each hemisphere deals with the world in its own way. For example, they have set up visual displays that are sent to either the left or the right hemisphere, but not both.

In most people language seems to be housed in the left half of the brain. If the left hemisphere of a split-brain patient sees an image, he or she can say what it is. But what if the right hemisphere sees something and the left side does not? In that case the patient cannot verbally identify the object but can point to it on a screen with the left hand.

Gazzaniga believes that the left hemisphere contains a mechanism that fabricates theories about the way the world works. He calls it the interpreter. Some of the interpreter’s theories try to explain why we feel and act as we do. In an interview by Science News, February 24, 1996, he stated:

“There seems to be a left-brain mechanism that’s constantly trying to find relationships between events that you encounter in the world and constantly assessing where you stand in relation to others.” As the article explained, researchers have noticed this phenomenon “in tests of split-brain patients shown two pictures simultaneously, one to each hemisphere. Participants then perused an assortment of additional pictures and chose the item most closely related to each of the original pictures. For instance, one man had a picture of a chicken claw flashed to his left hemisphere and a picture of a snow scene presented to his right hemisphere. From the ensuing selection of pictures, he correctly chose a shovel with his left hand (controlled by the right hemisphere) and a chicken with his right hand (controlled by the left hemisphere). When asked to explain his choices, he responded: ‘Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.’ Gazzaniga concluded that the left brain observed the left hand’s choice of a shovel – which stemmed from the right brain’s nonverbal, inaccessible knowledge [of the snow scene] – and proffered an explanation based its own fowl information” (http://pegasus.cc.ucf.edu/~fle/gazzaniga.html; paragraph breaks have been deleted).

Here’s the disturbing bottom line: It’s not just split-brain subjects who concoct false explanations of their own behavior and blithely believe these fictions, Gazzaniga has seen overwhelming evidence that “normal” people do the same thing. As Richard Feynman once put it, “The first principle is that you must not fool yourself, and you are the easiest person to fool.”*

Roger Christan Schriner

*(Quoted by Christof Koch, Consciousness: Confessions of a Romantic Reductionist, p. 159.)