Ouija board (Talking board or Spirit board) is a printed or written flat board with the letters of the alphabet, the numbers 0-9, the words “yes”, “no” and “goodbye”. One or more participants place their fingers on the heart-shaped or triangular planchette or the coin to spell out messages in response to the questions asked to the spirit called.
According to the Spiritual theory, ouija board is a channel to the spirits or ghosts and the ability to utilize the board correctly is determined by one’s magickal and spiritual training. It is regarded as an instant portal into the lower astral plance.
The modern automatism theory bases the phenomenon upon “ideomotor effect or response”. Ideomotor effect or Carpenter effect is a phenomenon wherein a subject performs motions unconsciously as a result of a movement mentally stimulated or watching another person moving. The Skeptic’s Dictionary defines the ideomotor effect as “the influence of suggestion or expectation on involuntary and unconscious motor behavior”. The “unconscious” or more specifically subconscious aspect of ideomotor effect is responsible for the sensation of external supernatural force controlling the movement.
Two principles of ideomotor action induction are distinguished: perceptual induction, in which people tend to perform the movements they see, and intentional induction, in which people tend to perform movements suited to achieve what they would like to see.
Carpenter provided a simple diagram in which he illustrated the basic ideo-motor reflex conceptualization of suggestion.
As per the book “A New Theory of Mind: The Theory of Narrative Thought”, in an experiment conducted by the author and his student on the ouija board, the dominant player (predicted by results on Need for Power test taken before the game started) always influenced the movement. The research showed that coherent communications that appear to both players to come from outside source are actually originating mostly in one player. 1A New Theory of Mind: The theory of narrative thought – Lee Roy Beach and Byron L Bissell
See what blindfolding the participants in the game of Ouija board yields.
According to Philip Shenefelt in the American Journal of Clinical Hypnosis, ideomotor actions happen when “intention or thought is transmitted to the motor cortex at a subconscious level, coordinated by the cerebellum, and sent down spinal nerves to the appropriate muscles, inducing movements not visible to the naked eye.” That’s when unconscious, muscular movement occurs. 2Shenefelt, Philip. (2011). Ideomotor Signaling: From Divining Spiritual Messages to Discerning Subconscious Answers During Hypnosis and Hypnoanalysis, A Historical Perspective. The American journal of clinical hypnosis. 53. 157-67. 10.1080/00029157.2011.10401754. 
Sunker Abaji Bisey said, “I have never been able to write anything intelligent upon an ordinary ouija board, but the fact that I am equally unable to write anything intelligible upon the board I have invented is the best claim I can advance that it is proof against the effort of any person to use it dishonestly. If any spirit has anything to say to me and will communicate it through the device which I have just invented then indeed I will believe that he is the spirit which he pretends to be.”