How split personalities work vary from fiction to fiction. Each one of them looks at it in a different way, with several key aspects to show:
- Are all identities the same?
- * do they use the same name? or are they different in the same way?
- * for example, Dr. Jekyll and Mr. Hyde, The Doctor and The Cyber-Planner
- Do they share the same body?
- * Is the body changed in any way?
- Do they split control of the body? or is it in full control by whoever is dominant?
- Do they share memories of the original personality?
- Do they share experiences, while the other is in power?
- Are they aware of each other?
- With Dr. Jekyll and Mr. Hyde, they shared the same body, but it was changed in the switch. Neither side was aware of what the other was doing.
- With the Nutty Professor, Sherman becomes more aware of Buddy, while Buddy becomes a distant voice in the back of his mind.
- In the Doctor Who Episode Nightmare in Silver, the control of the body was split between the Doctor and the Cyberplanner; they each had an arm, and the head was in control of the dominant personality. They are fully conscience at the same time, and have full access to the memories of the doctor and what he is thinking about; except the remaining .238% that was up to battle.
Needs a lot of work. :)