The Myth of Dual Consciousness in the Split Brain: Contrary Evidence from Psychology and Neuroscience

In his Nobel acceptance lecture in 1981, Roger Sperry, who was awarded the Prize for Physiology or Medicine, argued that his research and that of his collaborators had demonstrated that the right hemisphere of split-brain patients had a rich cognitive and emotional life that might be said to rival that of the left hemisphere in many respects. This cemented the belief that two consciousness may exist side by side, so to speak. Such a belief is not uncommon, even amongst distinguished researchers. It arose in great part because some split-brain patients have been afflicted by the “wild-hand syndrome,” in which the patient, say, would reach for an object with his right hand, only to have the left hand block or undue the action. This phenomenon made a strong impression on many observers, who then concluded that the two hemispheres, each with its own consciousness, were in conflict with each other. However, many considerations from psychology and neuroscience lead to a simpler and more nuanced explanation without recourse to extraordinary claims: The different hemispheres are conscious at different times, depending on the task. For example, in classical experiments by Gazzaniga and LeDoux, it seems obvious that the split-brain patient is not conscious of what his right hemisphere has processed. It is not merely that the patient is not able to verbalize his experience, or that he is confused. For the patient is quite confident, indeed adamant, that he has seen nothing, and even resorts to confabulation to explain his choices. Whatever mental process takes place in the right hemisphere clearly meets the McGovern-Baars operational criteria to qualify as an unconscious process. Moreover, lesions to the SMA also create the “alien hand syndrome” without any mysterious dual consciousness. The case of split-brain patients operates on similar mechanisms. Keywords-dual consciousness; split-brain; action control; operational definition; neuroscience