Split brain surgery is a technique severing the corpus callosum splitting the right and left hemispheres in half (Split). This is usually a last resort for people with epileptic seizures and has no bad effect on the person. People who go through this surgery suffer the effects of the brain not being able to analyze an object with both sides of the hemispheres which is quite interesting in studies. The left side of the brain is associated with speech-control and the right hemisphere is the understanding hemisphere of the brain. When these two are in unison they work together and help analyze, interpret, and express perception of the outside world. A way to show how this works is through experimentation which is the main source in figuring out why the brain acts the way it does when split (without the corpus callosum converging them together). For example, when a person with split-brain surgery is presented with an object on the left visual field the person will not be able to vocally (left side of the brain) understand what has happened, but can recall it through feeling/analyzing (right-side of the brain) the object. This is vice-versa when presented on the right visual field, the person will be able to speak of what they saw but will not be able to physically recall what the object was.
This surgery is quite fascinating as it is actually a cure for epilepsy seizures with minimal after-effects to the brain. I think this actually helped psychologists greatly through understanding the cognitive functions of the brain and is only a start into understanding the complexity of it.
To really think about it the brain itself really has two personalities which are brought together by the corpus callosum, but can be split through this surgery. The brain is quite an amazing complex organ in which can be defined by nothing due to the many functions it serves. This amazing surgery has saved lives of many people and can do much more, but it's up to the studies to really find out what's going on after this surgery.