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The Future of the Electroencephalography Test in Criminal Law - Matt Reimer

The criminal justice system has an important role in society. In a desire to keep the public safe, finding the true culprit of wrongs toward others is of the utmost importance. Since the beginning of time, society has desired the most efficient means of performing this difficult task. This was the context surrounding the creation of the polygraph, an instrument that has become almost larger than life as a “lie detector test”. Unfortunately, it often fails to fulfill its stereotypical function and has resulted in unfortunate errors at the expense of individual freedom and public safety. Its less than perfect reputation has made it consequently inadmissible in any criminal trial. As a result, the search has been on for an instrument that can do the impossible: reach into a person’s head and find their culpability. In recent years, much excitement has surrounded the Electroencephalography (EEG) test. Unfortunately, due to its similar pitfalls to the polygraph, the public should be wary of the EEG, until such pitfalls have fallen to the wayside.

Since its invention in 1921, the polygraph has been a fixture in various contexts where the truth is sought.[1] This includes criminal investigations. A common form of polygraph test in such a setting is the control question test (CQT). The test begins with the test taker answering a series of “control questions” which are similar to the offence being investigated but are in actuality irrelevant to any information that the authorities need. Such questions are, however, true to the experience of the person being tested.[2] The tester then assesses whether the subject is telling the truth based on three indicators. This includes their heart rate, breathing, and perspiration.[3] Since the control questions are true for the test recipient, each of the indicators should be at a high level due to that individual’s anxiety. If the actual investigative question is true for the test recipient, such answers should elicit either equally high or even higher indicators due to their anxiety having been asked a true question. If the actual question is not true for the test recipient, indicators should be functioning at a lower level compared to the control questions.[4]

Such a method has been shown to work within controlled settings between a rate of 83 and 95 percent.[5] Furthermore, police have been permitted to use polygraphs within their interrogations.[6] Throughout the twentieth century, the polygraph was used for a variety of aggressive objectives including the rooting out of communists during the red scare.[7] Despite widespread usage for many years, the polygraph is insufficient for admissibility within a criminal court. One reason for this is that each test-taker responds differently to the polygraph. Some may be nervous while continuing to answer truthfully while another individual may commit the inverse.[8] Another issue is the fact that a test recipient may have a medical condition or take medications that change their heart’s rhythm and other such responses.[9] Thirdly, polygraph efficacy tests have generally only occurred in controlled settings. A fourth factor is that control test responses have often been rigged by test takers in order to have a smaller statistical difference between their baseline and evidence-based questions.[10]

The effects of the third issue can be seen today. In the last twenty years, many studies have come out, citing lack of evidence for the polygraph’s reliability. Real-world consequences have stemmed from this as many known criminals have beaten the test or been falsely convicted because of it. KGB double agent Aldrich Ames and the wrongfully convicted Floyd Fay are examples of these respective phenomena.[11]

In contrast to the polygraph’s sensory functions, the EEG tests the human brain’s electrical activity. All the test administrator has to do is ask a question and upon the test taker’s answer, their brainwave patterns are tracked. For any recollection of a true event or insight, the brain’s response will be immediate while manufactured responses take much longer.[12] Proponents of the EEG test argue that it resolves many problems stemming from the polygraph. For example, individuals with anxiety will no longer test in an unconventional fashion. Health conditions, including those of the heart would also play less of a factor.[13]

Unfortunately, where old problems are addressed, new problems abound. As the EEG is a brain test, various factors may influence test results. This includes an individual’s age, working memory mental capacity, and other neurological factors. Such traits may influence one’s recognition or lack thereof regarding a question that is supposed to trigger a response.[14] Similar to the polygraph, there is also very little evidence outside of control tests regarding the EEG’s efficacy. Early studies reported 40 to 80 percent accuracy.[15] Although some improvements have been made, the test has been less effective among uncooperative persons who seek to game the EEG. Some measures used have included counting backward by 7s and other unexpected tricks that had an effect.[16] Although test proponents claim that such issues have been addressed, due to a lack of non-controlled tests, there is no telling what other issues might exist.

Based upon evidence attained thus far, it is safe to say that EEG shows more promise than that of a polygraph test. However, many issues remain yet to be resolved as tests outside of control test areas have not sufficiently occurred. In order to avoid missteps that came as a result of the polygraph, society should be warry of the EEG test. Until test information from non-controlled settings has come out and can confidently speak to the EEG’s reliability, society should hold similar tests at arm’s length.

[1] Amit Katwala, “The race to create a perfect lie detector – and the dangers of succeeding”, The Guardian (9 September 2019), online: <>. [2] “The Truth About Lie Detectors (aka Polygraph Tests)”, The American Psychological Association (5 August 2004), online: <>. [3] Ibid. [4] Ibid. [5] Glen Cook and LT Charles Mitschow, “Beyond the Polygraph. Deception. Detection and the Autonomic Nervous System.”(2019) 36(7) Federal Practitioner at 316-321. [6] R. v. Weldon, 2022 O.J. No. 5930. [7] Supra note 1 [8] Supra note 2. [9] Supra note 5. [10] Supra note 1. [11] Ibid. [12] R. Douglas Fields, “Nabbing Criminals by Using Brainwave Analysis”, Psychology Today (27 April 2020), online: <>. [13] Supra note 5. [14] Supra note 10. [15] Supra note 5. [16] Ibid.


The views and opinions expressed in the blogs are the views of their authors, and do not represent the views of the Faculty of Law, or the University of Manitoba. Academic Members of the University of Manitoba are entitled to academic freedom in the context of a respectful working and learning environment.


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