Lie detection

Overview
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.

Lie detection commonly involves the polygraph. Voice stress analysis may be also be more 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. This includes bodily reactions like skin conductivity and heart rate.

An fMRI can be used to compare brain activity differences for truth and lie. In episode 109 of the popular science show 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 technology still requires further development.

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.

Truth drugs such as sodium thiopental 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 subject that they cannot tell a lie while under the influence of the drug.

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.

Cognitive Polygraphy
Recent developments that permit noninvasive monitoring using functional transcranial Doppler (fTCD) technique led Njemanze to postulate 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, 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 United State Patent No. 6,390,979. A pattern of blood flow velocity changes is obtained in response to questions, that include Wrong and Correct 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.

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