In 1961, the war veteran W.J. experienced two major seizures a week. He had been suffering from this for ten years. After each attack, he needed at least one day to recover. He experienced no problems in other areas: he had a good sense of humor and was pleasant to deal with. However, the attacks were so unpleasant that he would do anything to get rid of these attacks. Dr. Joseph Bogen, a neurologist, suggested that W.J. would undergo a surgery that would cause his corpus callosum to be broken. The corpus callosum is a structure in the brain that connects the left and right hemisphere. Breaking the corpus callosum would therefore also break the connection between the two hemispheres. This surgery was also performed 20 years ago on a number of patients in New York. None of these patients suffered from side effects, while they all were cured from their seizures! Psychological studies also showed no differences in behavior or brain function after these surgeries. So, splitting the brain of humans seemed to have no consequences. Also, for W.J. the same seemed to be true: at first it seemed as if he did not experience any negative side effects, while his seizures were completely gone. The strange thing about these findings is that in animals that have undergone the same type of surgery, large differences were found in behavior and brain function. Researchers therefore thought it was strange that in humans there would be no consequences or whatsoever of splitting the brain. To investigate this further, W.J. was asked to participate in research to help solve this 'mystery'. A new research method was now used that was based on the anatomy of the optic nerve. This is a research method that was not applied 20 years ago to the patients in New York who underwent the same surgery. This anatomy means that stimuli presented in the...