Numerous researchers have noted the obvious parallels between hypnotic sleep and the trance state of the medium. In hypnosis the subject is controlled by the suggestions of the hypnotist. In the trance state, many investigators believe, the medium is controlled by autosuggestion—a kind of self-induced hypnotic state.
Good subjects for hypnosis can be made to assume any number of characterizations, from elderly people to babies, and will firmly appear to believe themselves to be the individuals they represent, complete with a set of habits and idiosyncrasies for the characters they are impersonating. Likewise mediums, through autosuggestion in the trance state, assume the guise of the spirit communicators who have come to speak to the sitters in the seance circle. Professional hypnotists have often claimed that all the phenomena of mediumship can be duplicated through their subjects by suggesting to them that they are under the control of discarnate entities.
A medium or a Spiritualist might counter such an assertion by saying that certain spirits may actually take possession of a hypnotic subject when they receive permission to do so, and that the subject may then truly be said to be in the control of the souls of the deceased.
Parapsychologists who have tested both the hypnosis hypothesis and the possibility of spirit possession have found that, in some instances, it is just as easy to obtain communication from a living person through a hypnotic subject or a medium as from a dead one, and from a fictitious person as from a real one, simply by making the proper suggestion to either entranced agent.
When mediums enter the trance state, they enter into a subjective condition that leaves them as open and amenable to the law of suggestion as is the subject of hypnosis. The potent suggestion that the spirit of a deceased person is about to enter their body and control them is ever present in the subjective mind of mediums. Such a suggestion has been a part of their educational development, and their religious beliefs are based on the "fact" of spirit survival and communication. All paranormal phenomena are considered by mediums to be a direct interaction of the spirit world with the material world. The trance state allows them to cooperate with spirit personalities and to become a vital link in communication between the two worlds. Since mediums believe so strongly in survival and their ability to establish contact with the departed, it is their mission to aid others in communicating with their beloved deceased.
Many parapsychologists theorize that with such a powerful autosuggestion constantly being directed to the transcendent or subjective level of the mind of a medium, all subjective knowledge gained by establishing telepathic rapport with the unconscious level of other minds will be immediately interpreted as information gained by the intercession of spirits. And so far as the transcendent mind of the medium is able to receive impressions of the "spirits," that mental image will be impersonated with all the creative abilities that reside in the almost limitless range of subjective intelligence.