The Split Brain Revisited; The Hidden Mind; Special Editions; by Michael S. Gazzaniga; 6 Page(s)

About 35 years ago in Scientific American, I wrote about dramatic new studies of the brain. Three patients who were seeking relief from epilepsy had undergone surgery that severed the corpus callosum-the superhighway of neurons connecting the halves of the brain. By working with these patients, my colleagues Roger W. Sperry, Joseph E. Bogen, P. J. Vogel and I witnessed what happened when the left and the right hemispheres were unable to communicate with each other.

It became clear that visual information no longer moved between the two sides. If we projected an image to the right visual field-that is, to the left hemisphere, which is where information from the right field is processed-the patients could describe what they saw. But when the same image was displayed to the left visual field, the patients drew a blank: they said they didn't see anything. Yet if we asked them to point to an object similar to the one being projected, they could do so with ease. The right brain saw the image and could mobilize a nonverbal response. It simply couldn't talk about what it saw.