Roger Sperry discovered and developed the concept of left brain and right brain theory. He found that the two hemispheres of the brain think differently - the left brain is more logical and methodical, dealing with language and numbers, while the right brain is more creative and intuitive, focusing on visuals, images, and emotions. Sperry proved this theory by studying patients who had undergone surgery to cut the corpus callosum connecting the two sides. Further research identified differences in how left-brained and right-brained people process information and make decisions.