Physical mediums are believed to produce materialization of spirits, apports of objects, and other effects such as knocking, rapping, bell-ringing, etc. by using "ectoplasm" created from the cells of their bodies and those of seance attendees.
Channeling can be seen as the modern form of the old mediumship, where the "channel" (or channeller) allegedly receives messages from "teaching-spirit", an "Ascended Master", from God, or from an angelic entity, but essentially through the filter of his own waking consciousness (or "Higher Self") [REF].