I'm curious what the extent of the ideomotor effect is, and how it is precisely defined.

I often hear it used to explain things as widely diverse as Ouija boards, assisted communication frauds, and even accidental animal training! (Clever Hans)

I don't doubt that some mechanism is at work, and I don't doubt it's powerful, but I often hear the ideomotor effect cited as a cause of a phenomenon, without it being really made clear HOW it's the cause.

I occasionally worry that it's being overused as an explanation in situations where "We don't know why" is the honest truth, and as such is a sort of skeptical version of the God of the Gaps fallacy.

What studies are there to support that the ideomotor effect is a real, measurable phenomenon?


3 Answers 3


The following argument is a "strong opinion, weakly held" - very weakly held. I am not offering it as a real answer, but instead as a deliberately provocative position to be attacked, in order to trigger some more robust answers than we have seen in skeptical publications. If we can't produce a more robust answer, perhaps it is time to question the theory.

When a dowser claims that "The corpuscles ... that rise from the Minerals, entering the rod, determine it to bow down" [William Pryce, 1778] I smile at the invented explanation that has no explanatory or predictive power.

When skeptics claim that dowsing is just the "ideomotor effect" [for example], I frown, because it sounds like just another invented explanation that has no explanatory or predictive power.

I recently read a passage in a Tom Stafford BBC Future story about the (unrelated) Zeigarnik Effect explaining that the term:

describes a phenomenon, but it doesn’t really give any reason for why it happens. This is a common trick of psychologists, to pretend they solved a riddle of the human mind by giving it a name, when all they've done is invented an agreed upon name for the mystery rather than solved it.

This immediately brought to mind this issue with the ideomotor effect.

I understand that there are volitive movements and reflexive movement [ref], but simply declaring that there is a third type of movement between the two (where our bodies secretly act in line with our expectations, without any conscious awareness), and referencing a study 150 years old to back it up, is not terribly convincing.

Even if a person has the expectation that the dowsing rods will cross, the idea that that will be automatically turned into exactly those movements requirement by the hands to enact such movement is an extraordinary claim. That those movements would turn out to be extremely subtle (as opposed to macro-level movements, immediately perceptible to anyone watching) is another extraordinary claim. Finally, that, unlike breathing or the reflex to retract from a hot surface, the conscious mind will be completely unaware of these movements (post hoc), even when thinking about them - seems quite unbelievable.

If skeptics are to dismiss many different paranormal effects as being due to the "ideomotor effect" they should have substantially more evidence (and preferably a model of the mechanism) than a Latin phrase and the same 1852 paper that seems to be the primary source to many of their documents.

It is not enough to prove that dowsing doesn't work under controlled conditions. If you are going to make the positive claim that dowsing appears to working under uncontrolled conditions purely through the mechanism of the ideomotor effect, you need to have some substantial evidence to support that the ideomotor effect exists and can meet all of the above extraordinary claims.

  • I don’t think that we need more than volitive and reflexive movements to explain this effect. I do agree that a comprehensive, empirically backed explanation should be available before we can use this effect to brush aside alternative explanations. Apr 2, 2012 at 13:06

The ideomotor effect article on Skeptic's Dictionary says of the effect:

The ideomotor effect refers to the influence of suggestion or expectation on involuntary and unconscious motor behavior. The movement of pointers on Ouija boards, of a facilitator's hands in facilitated communication, of hands and arms in applied kinesiology, and of some behaviors attributed to hypnotic suggestion, are due to ideomotor action.

That's just an excerpt. The whole thing is worth reading.


Ideomotor action simply refers to small, unconscious movements. Since they are so subtle, those tiny movements aren't normally studied directly, but they can be "magnified" into a larger, more measurable effects. One of the easiest to study is the hand-held pendulum:

The hand-held pendulum first came under scientific scrutiny during the early 1800s in studies by the highly regarded French chemist Michel-Eugene Chevreul. His investigation of the mysterious pendulum was prompted by an 1808 book published by a group of physicists who claimed "such phenomena were attributed to a new force which inaugurated a new chapter in physics." Chevreul found this theory scientifically unacceptable. (snip) The conclusions of Chevreul's study were reduced to a single principle: The swing pattern of the pendulum was caused by "nonconscious (involuntary) muscle movements initiated by autosuggestion." http://www.magician.org/portal/node/769

Sometimes called "Chevreul pendulum illusion", this effect has been widely studied (1975, 1996, 1998). A 1976 study by Easton and Shor, An experimental analysis of the Chevreul pendulum illusion, found that the effect was enhanced when the subject was concentrating harder, or when the subject was under more physical strain.

The pendulum test is sometimes used as a measure of a subject's susceptibility to suggestion when studying other phenomenon, like facilitated communication:

Next, ideomotor responsiveness was assessed via the Chevreul pendulum illusion (Easton & Shor, 1976). The stimulus was a pendulum consisting of a metal washer fastened to a 30-cm string. Participants were asked to grasp the end of the string and to hold the pendulum directly above a line on a page that was placed on the desk in front of them. Ideomotor responding was indicated by movement in the direction of the line. The Chevreul pendulum illusion can be produced either by asking people to imagine the pendulum moving in the indicated direction (Easton & Shor, 1976) or by asking them to prevent the pendulum from moving in the desired direction (Ansfield & Wegner, 1996). Facilitated Communication As An Ideomotor Response, Burgess et al, 1997 (PDF)

This study found a significant correlation between the subject's response to suggestion using the pendulum and their success at the facilitated communication tasks. (Facilitated communication involves a helper guiding the hand of an impaired patient to type messages using a keyboard; controlled studies such as this show the message is really coming from the facilitator, not the patient.)

With this background, then, research into other mysterious phenomenon typically involves identifying a plausible mechanism to magnify these small involuntary movements, and tests carefully designed to rule them out. One further example:

Dowsing typically involves a forked stick held at high tension, or one or two freely-pivoting wires held at their balance point. Small involuntary movements are magnified into dramatic dips or swings:

With one rod in each hand, I first demonstrated how dowsing works by holding the rods in front of me, aimed straight ahead and with their horizontal arms parallel to each other and to the floor. I then slowly walked about the room until the rods suddenly crossed one another. I walked away from that spot and showed how the rods uncrossed and became parallel again. I suggested that the place where the rods had crossed must be near a source of flowing water, perhaps a water pipe under the floor. I then requested that each of the students try the rods. To their amazement, the rods crossed when they walked over the spot I had indicated. ...

I did similar demonstrations for the second group of students. However, this time I let them see my dowsing rods crossing at a different arbitrarily chosen location in the room. Sure enough, for these students, too, the rods crossed just at the spot where mine had.
(How People Are Fooled by Ideomotor Action by Ray Hyman, originally printed in The Scientific Review of Alternative Medicine, 1999)

This seems to me to be a clear demonstration of how much subject expectation contributes to the effect, since it is unlikely these students had a stake in the outcome, like a professional dowser does.

Other related phenomenon include the "Clever Hans effect", named after a horse who appeared to be able to perform arithmetic, but was eventually shown to be responding to the (involuntary) cues of his trainer.

Further reading:

  • Can you bring some more sources into the answer? As it stands now the article sourced is more from a debunking standpoint and really doesn't seem back up it being accepted or well understood by the medical community.
    – rjzii
    Nov 8, 2012 at 15:05
  • I think the linked article itself is pretty well sourced, including some of the original work going back to the 19th century (to which I don't have direct access). And I would tend to think that any fair treatment of the ideomotor effect will read like a debunking, since the research itself is, by its very nature, debunking the traditionally offered "metaphysical" explanation for an effect like dowsing. But I'll see if I can find additional sources.
    – BradC
    Nov 8, 2012 at 15:25
  • Right, but seeing as how the question is if the effect is well understood and defined as opposed to if, say, dowsing works, we need to make sure that a robust explanation of it is provided. For example, while your answer provides a good summary as to how meaning can be applied to the effect, it doesn't provide an explanation as to how the effect itself arises which is needed for a proper explanation.
    – rjzii
    Nov 8, 2012 at 15:59
  • 1
    Rewritten with more and broader references
    – BradC
    Nov 8, 2012 at 18:13

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