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...