How the Split Brain Undermines Our Understanding of Consciousness

Human higher-order cognition is not what it seems.

David Wolman, The split brain: A tale of two halves, Nature 483, 260–263 (15 March 2012)
Dr. Brenda Milner

This young woman — NG — she blushed a little. Of course, emotion can get transmitted by lower centers that are not separated [by the commissurotomy surgery], you see. So, this patient probably felt a bit uncomfortable. And the left hemisphere said, “Oh, Dr. Sperry, what a strange machine you have there,” or made some comment about the machine, or what Sperry was doing. Because she obviously had no idea of what actually had happened — did not have access — but had access to the emotion and was rationalizing, trying to understand the way she was feeling, I suppose.

Dr. Michael Gazzaniga

To our surprise, our patient drew a bow and arrow! It appeared as though he had internally integrated the information in one hemisphere; that hemisphere had, in turn, directed the drawn response.

We were wrong. We finally determined that integration had actually taken place on the paper, not in the brain. One hemisphere had drawn its item — the bow — and then the other hemisphere had gained control of the writing hand, drawing its stimulus — the arrow — on top of the bow. The image merely looked coordinated. We discovered this chimera by giving less easily integrated word pairs like “sky” and “scraper.” The subject did not draw a tall building; instead he drew the sky over a picture of a scraper […] Finally, we tested to see whether each hemisphere could, on its own, integrate words. We flashed “fire” and then “arm” to the right hemisphere. The left hand drew a rifle rather than an arm on fire, so it was clear that each hemisphere was capable of synthesis.

Author of Darwin’s Apple: The Evolutionary Biology of Religion, a new take on the function and purpose of religion.

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