Mind Hacks has posted a report on the classic research that Roger Sperry and Michael Gazzaniga did in the 1970s with people suffering from epilepsy so severe that the corpus callosum of their brains had to be severed. This procedure effectively isolated the two hemispheres of their brain from each other. Although the effects are not at all obvious in normal conversation, when one contrives to direct different sorts of information to each of the independent hemispheres, the results are quite fascinating. Here is a link to a short video of Gazzinaga working with one such patient.