Voice stress analysis

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Voice Stress Analysis (VSA) technology is said to record psychophysiological stress responses that are present in human voice, when a person suffers psychological stress in response to a stimulus (question) and where the consequences may be dire for the subject being "tested."[1]

Support and criticism[edit]

In a study published December 7, 2013, the International Journal of Electrical, Electronics and Computer Engineering (IJEECE) found that Voice Stress Analysis (VSA) technology can identify emotional stress better than polygraph.[2]

Proceedings of the 2005 Hawaii International Conference on System Sciences, identified that VSA technology can identify stress better than chance with performance approaching that of current polygraph systems.[3]

In a three year study conducted by the U.S. Air Force Research Laboratory in Rome New York, on voice stress analysis, it was determined that the voice stress units tested were able to recognize stress in the spoken voice. Additionally, these units performed equally whether the voice was a live test or a recorded one. The study also provided the caveat that caution should be taken when using voice stress analysis in that it should only be used as an investigative tool and not relied on for a case conclusion.[4]

Federally funded research via the American Polygraph Association in the United States showed "little validity" in the technique.[5]

There is tension between the voice stress analysis community and the polygraph community, due to the fact that the polygraph is heavily regulated and has been subject to numerous detailed, contentious scientific studies, while voice stress analysis is largely unregulated. However, there are studies which show VSA results to be even slightly better than chance.[6]

In Anders Eriksson and Francisco Lacerda's article "Charlatanry in forensic speech science: A problem to be taken seriously" voice stress analysis is described as charlatanry, and that analysis of studies shows that these methods perform at chance levels. They argue that "there are serious ethical and security reasons to demand that responsible authorities and institutions should not get involved in such practices."[7] This article was criticized by manufacturers of voice stress analysis machines. Due to the controversy, the International Association of Forensic Linguists' peer-reviewed journal International Journal of Speech, Language and the Law withdrew the article. However, there have no subsequent studies that refute the findings contained within that article.[8]

Principle and origins[edit]

VSA is distinct from Layered Voice Analysis (LVA). The main difference in the method of operation between LVA and VSA is based on the analyzed frequencies ranges: while VSA focuses on the 8–14 Hz range which is recorded via an omni-directional microphone. LVA utilises components of the voice such as pitch and tone, which are conrollable by the user, also varying according to his/her emotions at time of utterance. Change of emotions produce unreliable results being not particularly relevant to a Detection of Deception (DOD) scenario.[9]


VSA technology together with validated testing protocols, is designed to protect the innocent and avoid 'false positive' results. VSA is designed to assist any investigation by establishing the veracity of a subject's verbal responses.[10]

There are no known physical countermeasures for VSA. Conversely according to Honts et al., the simple use of a 'tack' placed under the tongue of the examinee, to be used as a countermeasure, can reduce the accuracy of polygraph results from 98% to 26%.[11][12][13][14][15]

They are illegal to use in California without consent, although peace officers are exempt from this law.[16][17]

Many intelligence agencies as well as private forensic psychophysiologists worldwide utilise VSA in preference to polygraph technology.[dead link][18]

Methodology and accuracy[edit]

The recorded "micro tremors" in a person's voice are converted via the algorithm into a scorable voice gram. The discrepancy in researched accuracy may result from incorrectly trained or non-trained persons utilizing the technology incorrectly.[speculation?] This is evident by some Polygraphists trying to "test" VSA technology without having received accredited training in the use thereof.[19][verification needed]

In 2002, Clifton Coetzee, a polygraph and VSA instructor, devised a scoring method for voice grams incorporating the 'UTAH 7 Point' scoring system, as used by modern day polygraphists. Reactive or Responsive patterns are assigned a weighting of +3 to -3.[20]

The American Polygraph Association's website lists conclusions from multiple studies, into the accuracy of voice stress analysis as a means of detecting the subject's truthfulness. Some researchers or polygraph professionals cast doubt on the validity of the results of such tests; many describe the results as no better than chance.[21]

The National Academy of Sciences published a 2003 study on the polygraph, in which they concluded that the evidence of its efficacy is "scientifically weak."[22] According to the American Psychological Association, "most psychologists agree that there is little evidence that polygraph tests can accurately detect lies".[23]

Notable examples of use[edit]

Following the 2012 case in which George Zimmerman fatally shot Florida teenager Trayvon Martin, Zimmerman was given a voice stress analysis test by the police department of Sanford, Florida. He passed the test.[24] A videotape of the test was publicly released in June 2012.[25]


  1. ^ Ruiz, Selye, & Guell, 1990. Voice analysis to predict the psychological or physical state of a speaker. Published in Aviation, Space, and Environmental Medicine, 1990. Ruiz et al. reports that their “research suggests that psychological stress may be detected as acoustic modifications in the fundamental frequency of a speakers voice” and “that the fundamental frequency of the vocal signal is slowly modulated (8-14 Hz) during speech in an emotionally neutral situation. In situations demanding increased ‘mental or psychomotor’ activity, the 8-14 Hz modulation then decreases as the striated muscles surrounding the vocal cords contract in response to the arousal, thus limiting the natural trembling”
  2. ^ Patil, V. P., Nayak, K. K., & Saxena, M. "Voice Stress Detection", 2, 148-154. (PDF File) International Journal of Electrical, Electronics and Computer Engineering, IJEECE (online) ISSN 1748-8893.
  3. ^ Sprague, R. H. (2005). "Evaluation of Voice Stress Analysis Technology". HICSS 2005 38th Hawaii International International Conference on Systems Science (03-06 January 2005/Big Island, HI). Los Alamitos: IEEE Computer Society Press.
  4. ^ Haddad, D., Walter, S., Ratley, R., & Smith, M. (2001). "Investigation and Evaluation of Voice Stress Analysis Technologies." Rome Laboratory Report (AFRL-IF-RS-TM-2001-7), 18-19.
  5. ^ Refer NAS 2003 in reference to all APA related research projects.
  6. ^ Haddad, Walters Study 2002, doc 193832
  7. ^ Eriksson, Anders; Lacerda, Francisco (2007). "Charlatanry in forensic speech science: A problem to be taken seriously". (PDF File) The International Journal of Speech, Language and the Law. Equinox Publishing. IJSLL (print) issn 1748-8885 IJSLL (online) issn 1748-8893
  8. ^ "Lie Detector Company Threatens Critical Scientists With Suit". Slashdot. 2009-01-29. Retrieved 2009-02-02. 
  9. ^ The Diogenes Company. Retrieved 9 February 2009.[dead link]
  10. ^ Heisse, J. “Is The Micro-Tremor Usable? - The Micro-Muscle Tremor In The Voice.” U.S. House Subcommittee of the Committee on Government Operations, 1974. Heisse analyzed 91 known-conclusion criminal cases utilizing voice stress analysis and determined that "Audio stress analysis seems to be valid in detecting changes in various psycho physiological parameters so that a trained examiner utilizing standardized techniques can evaluate these changes and thus utilize the instrument in truth and deception".
  11. ^ Honts 1993
  12. ^ Honts, C. R., and Hodes, R. L., “The Effect of Simple Physical Countermeasures on the Detection of Deception," paper presented at meetings of the Society for Psychophysiological Research, Minneapolis, Minn., 1982.
  13. ^ Honts, C. R., and Hodes, R. L., “The Effects of Multiple Physical Countermeasures on the Detection of Deception," Psychophysiology 19:564-565 (abstract), 1982.
  14. ^ Honts, C. R., and Hodes, R. L., “The Effect of Simple Physical Countermeasures on the Detection of Deception," Psychophysiology 19:564 (abstract), 1982.
  15. ^ Honts, C. R., Raskin, D. C., and Kircher, J. C., "Detection of Deception: Effectiveness of Physical Countermeasures Under High Motivation Conditions," 1 paper presented at meetings of the Society for Psychophysiological Research, September 1983.
  16. ^ Cal Pen Code § 637.3
  17. ^ Cal Pen Code § 637.2
  18. ^ "Over 1700 Agencies Utilizing the CVSA". [dead link]
  19. ^ Chapman, J. Criminal Justice Department, Corning Community College, New York. "The Psychological Stress Evaluator As A Tool For Eliciting Confessions", 1989. Chapman selected 211 criminal responses at random from 2,109 known-conclusion responses where voice stress analysis was used to test suspects. Professor Chapman's study confirmed that voice stress analysis was accurate when utilized as a truth verification device and produced a confession rate of 94.8% of the responses where deception was indicated.
  20. ^ Coetzee, C. (2000). Truth Extraction: Eyes, Lies, Analyse ISBN 978-0-620-52413-1]
  21. ^ Cestaro, V. Department of Defense Polygraph Institute, Ft. McClellan, AL. "A Comparison Between Decision Accuracy Rates Obtained Using the Polygraph Instrument and the Computer Voice Stress Analyzer in the Absence of Jeopardy", August, 1995.
  22. ^ "Conclusions and Recommendations" The Polygraph and Lie Detection (2003) National Academies Press. p. 212
  23. ^ "The Truth About Lie Detectors (aka Polygraph Tests)". American Psychological Association. August 5, 2004. Retrieved August 14, 2013.
  24. ^ Kovaleski, Serge F. (May 16, 2012). "Trayvon Martin Case Shadowed by Series of Police Missteps". The New York Times. Retrieved May 22, 2012. 
  25. ^ Stutzman, Rene (June 21, 2012). "Tape released of Zimmerman’s re-enactment of Martin shooting". Orlando Sentinel.