The ideomotor effect

is a psychological phenomenon wherein a subject makes motions unconsciously. As in reflexive responses to pain, the body sometimes reacts reflexively to ideas alone without the person consciously deciding to take action. For instance, tears are produced by the body unconsciously in reaction to powerful emotions. Automatic writing, dowsing, facilitated communication, and Ouija boards have also been attributed to the effect of this phenomenon. Mystics have often attributed this motion to paranormal or supernatural force. Many subjects are unconvinced that their actions are originating solely from within themselves.
The term was first used in a scientific paper discussing the means through which the Ouija board produced its results by William Benjamin Carpenter in 1852. In the paper, Carpenter explained his theory that muscular movement can be independent of conscious desires or emotions.
Scientific tests by the English scientist Michael Faraday, the French chemist Michel Eugène Chevreul, and the American psychologists William James and Ray Hyman have demonstrated that many phenomena attributed to spiritual or paranormal forces, or to mysterious "energies," are actually due to ideomotor action. Furthermore, these tests demonstrate that "honest, intelligent people can unconsciously engage in muscular activity that is consistent with their expectations”. They also show that suggestions that can guide behavior can be given by subtle clues.
Some practitioners claim they can use the ideomotor effect to communicate with a patient's unconsciousness using a system of physical signals (such as finger movements) for the unconscious mind to indicate "yes", "no" or "I'm not ready to know that consciously".
A simple experiment to demonstrate the Ideomotor effect is to allow a hand-held pendulum to hover over a sheet of paper. The paper has keywords such as YES, NO and MAYBE printed on it. Small movements in the hand, in response to questions, can cause the pendulum to move towards key words on the paper. This technique has been used for experiments in ESP, lie detection and ouija boards. The validity of these experiments has not been proven.
Michael Faraday, FRS (1791 – 1867) was an English chemist and physicist (or natural philosopher, in the terminology of the time) who contributed to the fields of electromagnetism and electrochemistry.

William James (1842 –1910) was a pioneering American psychologist and philosopher who was trained as a medical doctor. He wrote influential books on the young science of psychology, educational psychology, psychology of religious experience and mysticism, and on the philosophy of pragmatism. He was the brother of novelist Henry James and of diarist Alice James.

James defined true beliefs as those that prove useful to the believer. His pragmatic theory of truth was a synthesis of correspondence theory of truth and coherence theory of truth, with an added dimension. Truth is verifiable to the extent that thoughts and statements correspond with actual things, as well as the extent to which they "hang together," or cohere, as pieces of a puzzle might fit together; these are in turn verified by the observed results of the application of an idea to actual practice.