Author’s Native Language:
Can you trust the lie detector or the polygraph? Trust is the one of the most controversial topics about the use of the polygraph. Based on scientific knowledge, it is not possible to say whether the polygraph is really reliable at the levels indicated by certain studies [> 90%].
Without a doubt, if a person believes that that machine is capable of “extracting” the truth, they will be more prone to tell it spontaneously. This is a secondary use of the polygraph: a psychological deterrent that makes persons tell the truth on their own.
We see this use in a Netflix documentary “American Murder: The family next door“. Using first-hand footage, this documentary examines the disappearance of Shanann Watts and her daughters and the horrific events that followed.
The term and concept are due to Hans Driesch, the developmental biologist, later applied by Ludwig von Bertalanffy, the founder of General Systems Theory, and by William T. Powers, the founder of Perceptual Control Theory.
With this speech, she demonstrates her intention to create the conviction that the machine will be able to extract the truth. Which is far from correct, even considering the best estimates of polygraph accuracy.
I can say this based on its own functioning. The polygraph is a machine that has sensors to measure changes in the Autonomic Nervous System.
The polygraph does not extract the truth. Instead, it records changes in the nervous system, which can occur for a variety of reasons, including phenomena unrelated to lying. This is explained by the application of the principle of equifinality to human behavior.
In the case of the suspect shown in the documentary, almost immediately, he begins to confess to the crime in which he murdered his wife and two daughters.
So, in this case, the polygraph was used as a persuasive device and not as an truth extractor. Nonetheless, the result was a confession made by the suspect [because he believed the investigator’s conversation] and the solution of the crime.
Some interesting questions about trusting the lie detector
Can someone fool the polygraph?
Yes! This is done by altering physiological signals when answering control questions [questions that the person cannot lie to], such as confirming the mother’s name or age.
Usually, the person achieves this goal by producing pain [biting their tongue, pressing their toes] or imagining something traumatic [1].
Can someone fail the polygraph even if they tell the truth?
Yes! Some people who are telling the truth may fail polygraph tests because they try to control their body’s responses [2].
Does taking drugs [muscle relaxants and others] affect the polygraph result?
Yes! Antidepressants, such as lithium, Prozac, Valium, Xanax and beta blockers, can affect the result of a polygraph exam [3], as their effect is to alter physiological reactions to certain emotions. However, before the test, you will be asked if the subject is taking any type of medication.
Is it possible to say that the polygraph is accurate?
The American Polygraph Association, which sets standards for these tests, says polygraphs are “highly accurate,” citing an accuracy rate of over 90% [4] when done correctly.
Critics, however, say that the accuracy of the tests is between 50 and 70% and the results are not reliable [5].
Final words
In 2010 I acquired a polygraph to carry out tests in my classes, showing that relying on the lie detector is no better than using close observation of behavior.
Remember:
I think its use has become popular in some countries due to the fact that there are people who are always looking for objective and scientific means to demonstrate its theses. In this case, it seems to me that they rushed….
To learn more about polygraphs and lie detection techniques see:
Drugs and the theater of lies.
The lie through brain impressions< /p>
What’s the latest in lie detection?
What are the techniques for detecting lies?
Keep following us up. Sergio SennaReferences
[1] Widacki, J. (2018). James Q. Murdoch: How to Pass a Polygraph, San Bernardino 2018, 23 pp. European Polygraph, 12(1 (43)), 35-36. [2] Faigman, D. L., Fienberg, S. E., & Stern, P. C. (2003). The limits of the polygraph. Issues in Science and Technology, 20(1), 40-46. [3] Cook, L. G., & Mitschow, L. C. (2019). Beyond the polygraph: deception detection and the autonomic nervous system. Federal Practitioner, 36(7), 316. [4] Honts, C. R., Thurber, S., & Handler, M. (2021). A comprehensive meta-analysis of the comparison question polygraph test. Applied Cognitive Psychology, 35(2), 411-427. [5] Ben‐Shakhar, G., & Iacono, W. (2021). Fallacies in the estimation of the validity of the Comparison Question Polygraph Test: A reply to Ginton (2020). Journal of Investigative Psychology and Offender Profiling, 18(3), 201-207.Article about the polygraph [lie detector] and its reliability. [in English]
This post is also available in pt_BR.