The ideomotor effect was first recognised as early as the beginning of the 19th century, although Carpenter did not name it as such until 1852. It came to be recognised when scientists looked into 19th century fascinations such as dowsing, pendulums, table tipping in séances, automatic writing, Ouija boards etc. It being a non-paranormal explanation for the results of these practises.
In more modern times, the ideomotor effect has shown itself to be prevalent in medical quackery, especially in the diagnosis of ailments. Radionic devices; chiropractors' rubbing plates; applied kinesiology; and radiesthesia, medical dowsing often with crystals; are examples of where the ideomotor effect is what is actually going on rather than real medical diagnosis.
Another disturbing area where the ideomotor effect shows up is in the pseudoscientific practise of "facilitated communication". This is where people who are otherwise unable to communicate, due to say autism or cerebral palsy, have their hand held over a keyboard by a person known as a "facilitator". When asked questions, the disabled person is now able to communicate with help from the facilitator by typing out answers on the keyboard.
Of course what is really going on is that it's the facilitator who's giving the answers; albeit unconsciously.
1.The ideomotor effect causes small, unconscious motor movements because of the person's expectations, preconceptions or suggestibility.
2.The person is not aware that they are causing the movements; therefore they ascribe the movement to an external force or power. The movement feels unnatural.
3.The "external forces" perceived are usually thought of as being paranormal in nature.
4.The effect is real and therefore can be repeated. This can lead to self-reinforcement of the paranormal explanation of the effect, which can create a belief in some special paranormal ability.
5.Once a belief is formed and reinforced, the believer does not usually ever give it up. Dowsers, healers, etc., who continually fail to pass objective, scientific tests do not give up their belief: they tend to make (often fantastical) excuses for their failures rather than accept a rational explanation for their "ability".
The ideomotor effect has been known for over 150 years, yet it is still not a widely known phenomenon. It tends to be used, rightly, as an explanation for dowsing and the Ouija board. Its scope however, is much wider than that and it should be a more widely known explanation for delusions, especially those of medical quacks.
The ideomotor effect is a classic example of how we can be fooled by our senses and ourselves. Many people believe in things because they have experienced them for themselves; they trust in the perceived infallibility of their senses.
The ideomotor effect is just one example of why we should use objective, scientific testing rather than rely on subjective, personal experience to work out what is real and what is not.