Complex sentence: His research on the hidden observer during hypnotic pain management was intended provided support for his neodissociationist theory, which held that a person undergoing hypnosis can still observe his/her own pain without consciously experiencing any suffering.
Split into simpler sentences: His research on the hidden observer during hypnotic pain management was intended provided support for his neodissociationist theory. This theory held that a person undergoing hypnosis can still observe his or her own pain without consciously experiencing any suffering.