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The Truth About The Lie Detector Test


The polygraph, more commonly known as the lie detector test is a great topic to explore with your students. A staple of reality TV shows and movie crime dramas, it is highly likely that the majority of your students will have some idea of what a polygraph is. In fact, asking them to share their knowledge on the subject would be a good place to start in class.


Another useful starting point – particularly in order to encourage critical thinking – would be to mention that the term “lie detector” is actually a misnomer. A polygraph test simply measures a person's physiological responses when answering questions; most typically, blood pressure, heart rate, sweating (galvanic skin response) and respiration (breathing rate). This is done in order to look for signs of autonomic arousal, from which deception can be inferred.


“Surely one of the most pernicious misnomers in psychology, the term "lie detector test" is often used synonymously with the storied polygraph test. This test is misnamed: it is an arousal detector, not a lie detector because it measures non-specific psychophysiological arousal rather than the fear of detection per se.” (Scott Lilienfeld).


The History of The Lie Detector


Investigating the link between physiology and deception has a long history within psychology. In 1915, William Moulton Marston began to study the physiological symptoms of deception during his time as a graduate student at Harvard University; as a result, Marston would go on to develop the first systolic blood pressure deception ('lie detector') test.



This wonderful (pun intended) image from the papers of William Moulton Marston, housed at the Schlesinger Library, shows Marston conducting one of his many experiments on blood pressure and deception.  


The person in the photograph taking notes; sporting a distinctive bracelet which looks like it could be used to deflect bullets, is Olive Byrne, the inspiration behind Wonder Woman, the superhero character created by William Moulton Marston under the pseudonym Charles Moulton.


The fact that it was a psychologist who created, wrote and produced the Wonder Woman comic strip is something students will no doubt interesting. Marston’s work on lie detection is the reason why Wonder Woman has a Lasso of Truth!


Can A Polygraph Really Detect Lies?


The scientific evidence would suggest not. The American Psychological Association notes that:


...most psychologists and other scientists agree that there is little basis for the validity of polygraph tests", and that "the most practical advice is to remain skeptical about any conclusion wrung from a polygraph.


in 2002, a committee commissioned by the National Academy of Sciences to review and report on the scientific evidence on the polygraph, stated that:


“Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy. Although psychological states often associated with deception (e.g., fear of being judged deceptive) do tend to affect the physiological responses that the polygraph measures, these same states can arise in the absence of deception.”


Class Discussion/Project Ideas


  • What are the most likely reasons for a false-positive result i.e. when a polygraph labels an honest individual as dishonest?
  • In what other ways is it believed that we can identify the deceitful e.g. reading body language? How valid are these alternative approaches to lie detection?