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Mark Dombeck, Ph.D.Mark Dombeck, Ph.D.
Essays and Blogs Concerning Mental and Emotional Health

The New Science of Lie Detection

Mark Dombeck, Ph.D. Updated: Sep 7th 2006

Time Magazine's online version recently posted a very nice article summarizing various new lie-detection technologies that are or may shortly become alternatives to the traditional polygraph technology.

The name "polygraph" betrays its function. "Poly" means "many", while "graph" means to write or record things. So a polygraph is a device for recording many signals. The signals that a polygraph measures and records are body signals of various kinds, including heart and breath rates, and skin conductance (how easily the skin resists or passes a weak electric current; something that varies with how much sweat a person produces). All of these body signals tend to change when people lie. The theory (in an oversimplified nutshell) is that lying produces a sort of anxiety that is expressed unconsciously and physiologically (through the body) even though it is denied at the verbal level.

Polygraph machines are thus essentially a biofeedback devices. Where a traditional biofeedback device that might be used for self-therapy would provide feedback to the person producing the signal, a polygraph gives feedback to law enforcement types who are looking for evidence.

Even with a trained and skillful administrator, polygraph technology is not altogether perfect at detecting lies. There is a lot of variability in how different people react when lying first of all. The act of being measured tends to produce anxiety which creates the potential for false positives. The worst part is that there are people out there who are so good at lying that they believe their own lies (or at least are in large part nonreactive) and thus don't perturb the polygraph. Because of these flaws, there is a lot of interest in alternatives.

The promising candidates for polygraph alternatives or adjunctive technologies are fMRI, EEG/ERP, eye scan techniques and Paul Ekman's facial coding system. I'll leave it for the article to describe how these newer technologies work, but in the end they are just more subtle versions of the polygraph, I think, and end up suffering from the same root problems that plague the polygraph.

IMHO, the most promising lie detection technology is probably the least technologically dependent one; namely Ekman's FACS. It costs much less than these other "device-oriented" techniques, and is much easier to train people to use. It is also the only technique that can be easily used in a natural setting. While it may not ultimately be as sensitive as an EEG, it will be ultimately far more cost effective to disseminate. In these budget challenged and highly terrorized times, it is exactly the sort of screening technology we most need.

Mark Dombeck, Ph.D.

Mark Dombeck, Ph.D. was Director of Mental Help Net from 1999 to 2011. Presently, he is an Oakland Psychologist (Lic#PSY25695) in private practice offering evidence-based acceptance and commitment therapy (ACT) and cognitive behavioral therapy (CBT) and addressing a range of life problems. Contact Dr. Dombeck by calling 510-900-5123, send Dr. Dombeck email or visit Dr. Dombeck's practice website for more information.

Reader Comments
Discuss this issue below or in our forums.

Tourette can influence a polygraph - Edwin - Nov 26th 2014

Coz of Tourette  one may have involuntary muscle spasms. These may influence the polygraph.
More important though: Since contracting Pelvis muscles is done as a 'trick' to get 'good' results during a polygraph test, someone with Tourette taking the test may be accused  of trying toinfluence he has something to hide.
So: if positive "you are guilty" If negative: inconclusve, but trying to hide something =>guilty

I have terets - Norman - Jan 27th 2012

I would really like to know this too. My terets manifests itself on a physical non-verbal form. I'm a nervous person in general and may have a polygraph test to take and even though I have nothing to hide every time I even think about this dam test I get my twitches real bad. I need to know. Will this make me fail? Should I refuse the test?






Tourettes syndrome - DT - Oct 23rd 2009

Can Tourette's syndrome cause false positives (or would that be negatives?) on polygraph exams?

In other words, can it make the test inconclusive or give what would seem like a lie, even though the person is telling the truth?

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