Final answer:
The theory that involves a split in consciousness during hypnosis is Dissociation.
Step-by-step explanation:
The theory that involves a split in consciousness during hypnosis is B. Dissociation. According to this theory, hypnosis is considered a dissociated state of consciousness, where the subject is focused on the hypnotist's suggestions with part of the brain while remaining conscious of other stimuli. This theory is supported by research into hypnosis and pain, which has shown a dissociation of consciousness while in a hypnotic state.