The procedure worked well as a "cure" for patients who suffered from severe epilepsy and did not respond to anti-epileptic drugs. It was soon discovered that patients who had a commissurotomy had some interesting difficulties. Patients were not able to communicate information from one hemisphere to the other, almost as though they now had two separate brains.
Here is an example of a standard experiment done to examine split brain perception.
Sperry and other scientists proceeded with further experimentation in order to determine the relationship between the right and left hemispheres of the brain. How (and what) the hemispheres communicate would provide valuable insight into the "mind" of a split brain patient. How did a commissurotomy affect one's perceptions of the outside world?
In one experiment, a word (for example "fork") was flashed so only the right hemisphere of a patient could receive the information. The patient would not be able to say what the word was. However, if the subject is asked to write what he saw, his left hand would begin to write the word "fork". If asked what he had written, the patient would have no idea. He would know that he had written something, he could feel his hand going through the motion, yet he could not tell observers what the word was. Because there is no longer a connection between the two hemispheres, information presented to the right half of the brain cannot convey this information to the left. Interestingly enough, the centers for speech interpretation and production are located in the left hemisphere. Similarly, if the patient is blindfolded and a familiar object, such as a toothbrush, is placed in his left hand, he appears to know what it is; for example by making the gesture of brushing his teeth. But he cannot name the object to the experimenter. If asked what he is doing with the object, gesturing a brushing motion, he has no idea. But if the left hand gives the toothbrush to the right hand, the patient will immediately say "tooth brush".
Micheal Gazzaniga, who did his graduate work in Sperry's laboratory, did further experiments which showed the attempts of the left hemisphere to compensate for it's lack of information, as well as attempts by the right hemisphere to get it's knowledge conveyed.
These experiments, pioneered by Sperry and colleagues, provided insight into the functionings of the two hemispheres and how they are different.