Split-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree.

The surgical operation to produce this condition is called corpus callosotomy. It is performed rarely, usually as a last resort in otherwise intractable epilepsy: to mitigate the risk of accidental physical injury by reducing the severity and violence of epileptic seizures.

A patient with a split brain, when shown an image in his or her left visual field (that is, the left half of what both eyes see), will be unable to name what he or she has seen.

This is because the speech-control center is in the left side of the brain in most people, and the image from the left visual field is sent only to the right side of the brain.

(Those with the speech control center in the right side will experience similar symptoms when an image is presented in the right visual field.)

Since communication between the two sides of the brain is inhibited, the patient cannot name what the right side of the brain is seeing. The person can, however, pick up and show recognition of an object (one within the left overall visual field) with their left hand, since that hand is controlled by the right side of the brain.