Lie detection  

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Lie detection is the practice of determining whether someone is lying. Activities of the body not easily controlled by the conscious mind are compared under different circumstances. Usually this involves asking the subject control questions where the answers are known to the examiner and comparing them to questions where the answers are not known. Critics claim that "lie detection" by use of polygraphy has no scientific validity because it is not a scientific procedure.



Lie detection commonly involves the polygraph. Voice stress analysis may also be commonly used because it can be applied covertly to monitor voice recordings. The polygraph detects changes in body functions not easily controlled by the conscious mind. These include bodily reactions like skin conductivity and heart rate.

Cognitive polygraphy

Recent developments that permit non-invasive monitoring using functional transcranial Doppler (fTCD) technique showed that successful problem-solving employs a discrete knowledge strategy (DKS) that selects neural pathways represented in one hemisphere, while unsuccessful outcome implicates a non-discrete knowledge strategy (nDKS). A polygraphic test could be viewed as a working memory task. This suggests that the DKS model may have a correlate in mnemonic operations. In other words, the DKS model may have a discrete knowledge base (DKB) of essential components needed for task resolution, while for nDKS, DKB is absent and, hence, a "global" or bi-hemispheric search occurs. Based on the latter premise, a 'lie detector' system was designed as described in Template:US Patent. A pattern of blood-flow-velocity changes is obtained in response to questions that include correct and incorrect answers. The wrong answer will elicit bi-hemispheric activation, from correct answer that activates unilateral response. Cognitive polygraphy based on this system is devoid of any subjective control of mental processes and, hence, high reliability and specificity; however, this is yet to be tested in forensic practice. See also cognitive biometrics.


An fMRI can be used to compare brain activity differences for truth and lie. Research does not currently support the use of fMRI to detect deception in "real world individual cases" (Kozel et al., 2004).

In episode 93 of the TV program Mythbusters, the three members of the build team attempted to fool an fMRI test. Although two of them were unsuccessful, the third was able to successfully fool the machine, suggesting that fMRI-based lie detection still requires further development.

Brain observations

Electroencephalography is used to detect changes in brain waves.

Brain fingerprinting uses electroencephalography to determine if an image is familiar to the subject. This could detect deception indirectly but is not a technique for lie detecting.

Cognitive chronometry, or the measurement of the time taken to perform mental operations, can be used to distinguish lying from truth-telling. One recent instrument using cognitive chronometry for this purpose is the Timed Antagonistic Response Alethiometer, or TARA.

Brain-reading uses fMRI and the multiple voxels activated in the brain evoked by a stimulus to determine what the brain has detected, and so whether it is familiar or not.


Truth drugs such as sodium thiopental and marijuana (historically speaking) are used for the purposes of obtaining accurate information from an unwilling subject. Information obtained by publicly disclosed truth drugs has been shown to be highly unreliable, with subjects apparently freely mixing fact and fantasy. Much of the claimed effect relies on the belief of the subjects that they cannot tell a lie while under the influence of the drug.


In the peer-reviewed academic article "Charlatanry in forensic speech science", the authors reviewed 50 years of lie detector research and came to the conclusion that there is no scientific evidence supporting that lie detectors actually work. Lie detector manufacturer Nemesysco sued the academic publisher for libel and forced a removal of the article from the online databases. In a letter to the publisher, Nemesysco's lawyers wrote that the authors of the article could be sued for defamation if they wrote on the subject again.

The cumulative research evidence suggests that machines do detect deception better than chance, but with significant error ratesTemplate:Citation needed and that strategies used to "beat" polygraph examinations, so-called countermeasures, may be effective. Despite unreliability, results are admissible in court in some countries such as the United States.

Clark Freshman, Professor of Law at University of California, Hastings College of Law, studies lies in negotiations and lies involving lawyers. Together with Michael Wheeler at Harvard Business School, he developed a series of clips of how lies – and concealed emotions – show up in real estate negotiations Template:Citation needed. His scholarship on lies and negotiations goes well beyond Paul Ekman's original theories. According to Ekman in his book Lie to Me, people expect lies in negotiations so Ekman doubted lies would reveal themselves with the same clues as in other areasTemplate:Citation needed. But Freshman and Wheeler found microexpressions of emotion and other clues in their research on negotiation.

See also

Unless indicated otherwise, the text in this article is either based on Wikipedia article "Lie detection" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on research by Jahsonic and friends. See Art and Popular Culture's copyright notice.

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