Dr. Harold Nemur is a psychologist who comes up with the idea of Charlie's brain surgery to increase his intelligence, while Dr. Jayson Strauss is a neurosurgeon and psychiatrist who carries out the operation and later sees Charlie for therapy. As Charlie says at the beginning of the book, even when he can't understand everything the two doctors are saying, "it sounded like Dr. Strauss and Burt was [sic] on my side and Prof Nemur wasn't" (page 10).
As the story goes on, Dr. Strauss is more sympathetic towards Charlie than Dr. Nemur. Dr. Nemur sees Charlie simply as an experiment and forces him to go through mazes and take puzzles again and again, with little regard for how Charlie is feeling. Dr. Strauss, on the other hand, attempts to help Charlie and is attentive to how Charlie feels. Dr. Nemur grows frustrated when Charlie asks questions about how to use the special TV that is supposed to help him gain knowledge, while Dr. Strauss thinks it's important for Dr. Nemur to explain how it works to Charlie. Dr. Strauss also helps Charlie adjust the TV so that he can sleep (page 27), as the TV was keeping him awake.
Dr. Strauss is not afraid to show Charlie what he doesn't know. For example, he tells Charlie, "I'm an even worst linguist than he is," (page 138), referring to Dr. Nemur. On the other hand, Dr. Nemur won't show his vulnerable or human side to Charlie and continues to treat him like he is simply a lab rat. To Dr. Nemur, Charlie is merely an experimental subject, while Dr. Strauss treats Charlie like a human being.