Symptoms of a Liar: Do Lie Detectors Really Work?

written by C.W.S.

How often have we watched this very scene in television and movies: a shadowed room with a single table and chair, a shifty character hooked up to several wires, a clip placed on the tip of his finger, a circle of lamp light on his face. Beside him, a stoic man with his glasses on the end of his nose asks questions neutrally, making check marks with a red pen while the machine’s meter scribbles lines across a ream of paper. Sweat appears on the brow of the test-taker, and then the question is asked: Did you kill her? The meter spikes, the red pen circles the lie.

Polygraph examinations, also known as lie-detector tests, have become so ingrained in our conception of criminal justice that most don’t consider questioning their validity. But just how accurate are these machines? The shocking April 2015 Washington Post story about the FBI’s use of flawed testimony in the area of microscopic hair comparison has shed light on some other methods used to judge innocence and guilt. Though polygraph evidence is rarely permitted in court, it is still used to point investigators in the direction of the guilty, and can affect their opinions of suspects.

History of lie detection

In ancient China and India, a test called the “spitting method” was used to tell if people were lying. They would fill the mouths of suspected liars with uncooked rice, and if it stuck inside their mouths or if the grains were dry when they were spat out, the person was suspected to have a dry mouth, a sign of lying.

Torture was also common. In the Middle Ages boiling water was believed to be a good test of honesty, with honest men withstanding the burns better than those who were liars. Critics of the polygraph also point to the witch trials of both Europe and the United States in which a an accused witch was thrown into a raging river, and if she was able to climb out and save herself, she was using witchcraft to do so, and if she drowned she was not a witch—but she was dead anyway. 

The Italian criminologist Cesare Lombroso created the earliest version of the modern polygraph in 1895, a device that measured changes in blood pressure for police investigations. A 1911 article in The New York Times showed the early faith in such technologies. Then called a psychometer, the article expresses a belief that the polygraph will soon replace all the human aspects of the criminal justice system: “The state will merely submit all suspects in a case to the tests of scientific instruments and as these instruments cannot be made to make mistakes nor tell lies, their evidence will be conclusive of guilt or innocence, and the court will deliver sentence accordingly.”

Leonarde Keeler testing his polygraph machine   

Leonarde Keeler testing his polygraph machine


Multiple people would put out similar versions of the polygraph over the next few decades—in fact, almost every source seems to name a different inventor. An incomplete project by William Marston brought the research to America, where Marston worked with a machine that studied blood pressure of German POWs. He apparently found that blood pressure and lying have a strong correlation. He lobbied for the courts to begin using his invention and in 1938, the same year that he published his research in a book titled The Lie Detector Test, Marston was hired by the Gillette razor company to star in a advertisement in which the lie detector was used to prove their razors superiority over the competition.

It was in 1921 that the first polygraph was used by law enforcement in Berekley, CA. One of the competing inventors of the modern polygraph, Leonarde Keeler, was friends with Berekley’s first police chief, August Vollmer. Vollmer had been seeking ways to reform police methods dealing with interrogation which were often violent, and he believed he had found it in Keeler’s invention. The belief was that, even if the “truth box” couldn’t detect a liar, it could make a liar nervous enough to confess if they were made to sit all night in a cell believing that they would be found out in the morning.

Modern polygraphs

Lie detector tests don’t detect lies. What they actually detect is nervousness which isn’t always indicative of a lie. It is believed that people who are telling the truth will not experience the nervous excitement of a person who is lying, but of course that isn’t always the case. Simply being given a test that measures your nervousness may be enough to make normal people nervous, thus generating false results. There are no bodily reactions that every person shares that can tell, without a doubt, that they are lying.

Modern polygraphs tests three levels of nervous system arousal: heart rate/blood pressure, breathing patterns, and sweating. It does so with the use of several monitors: a sensor wrapped around the lung-area to measure changes in respiration, one the arm to check blood pressure changes, and two sensors attached to the fingers to check changes in pulse and sweat. The hope is still the same as the older models: that there are a set of symptoms that prove deception.

The examiner will ask several control questions in order to measure normal bodily response rates. They will also ask broad questions that will trigger a nervous response, such as “Have you ever told a lie to a loved one?” The idea is that an innocent person who is telling the truth will have a more extreme rate of reaction to these broad questions than to the questions that are more specific and pointed, such as “Did you know the victim personally?”

Although in most cases polygraph results are not admissible in court, they do still play a serious role in determining who ends up as a defendant. Often, polygraphs are used as a tool to create enough apprehension to garner a confession. A well-known critic of the polygraph and co-founder of, George Maschke, conceded that there was some merit to the test: “if a criminal can be convinced by an examiner he’s been caught in a lie, he might give a confession that can be corroborated by other evidence like the location of a body or details about a murder weapon that only the murderer would know.”

Failures of the polygraph

Because the tests are given to humans by humans, there will always be a level of error. There are examples of circumstances that can negatively affect the test’s validity as well as ways that people have learned how to beat the test.

The examiner-subject relationship can certainly alter the results of polygraphs. If there is a negative interaction to begin with, say an examiner who has the air of interrogator, the subject may be more nervous than if they had an examiner they believed to be neutral. In addition, the examiner themselves has some level of power over the results, as they are subjective and interpreted by the examiner.

The experience of being hooked up to an invasive machine can also trigger nerves in some subjects, as well as the duration of the test. Examinations usually take around two to three hours, which can lead to feelings of exhaustion and nervousness in more sensitive subjects.

There are also many websites and individuals touting information about how to beat these examinations. They teach that drugs like anti-anxiety medications and sedatives can be used to calm the nervous system. They also teach people to envision terrifying things during the control period of the test, so that their typical response rates read similarly to the specific questions that would create nervousness later on. They also tell the subject to keep calm during the next portion, the directions verging on meditation: picture gentle waves rolling onto a beach, feel the sun on your face.

Serial killer Gary Ridgeway passed a polygraph examination by "just relaxing"

Serial killer Gary Ridgeway passed a polygraph examination by "just relaxing"

The most famous example of the dangers of trusting in a machine to measure the truth came with Washington State serial killer Gary Ridgeway. In 1987, Ridgeway was given a polygraph test and was able to pass by simply employing methods of relaxation. Ridgeway would go on to kill 49 women in total, including multiple women after the polygraph examination. Another suspect failed the test and became the primary suspect but was later cleared of all charges.

Jeff Deskovic was convicted of the rape and murder of a girl from his high school. The examiner told Deskovic that he had failed the test. He accused him of being a murderer. He used the fear of the test results to get a false confession from Deskovic, and Deskovic served 16 years in prison before being exonerated.

Those who are in support of the polygraph, mainly the American Polygraph Association, claim that lie detector tests have an accuracy rate of 90 percent. However, almost all other scientific platforms that deal with the polygraph say that it is lower, sometimes by a lot. Andy Morgan, a forensic psychologist at Yale University, thinks a polygraph’s accuracy is only slightly better than flipping a coin: “We actually know the polygraph, in the way that it is mainly used, is not better than chance at detecting deception. Maybe slightly at 52, 53 percent.”

So should a tool that is so heavily debated be used in investigations? The evidence may not be permissible in court but it is in the investigation, long before the courts hear evidence, where critics say the polygraph can cause manipulation. Those in favor of the method say it is a tool, just like any other, that can help detectives assess suspects, and a nonviolent method of attaining confessions.

We want to believe that we can tell when someone is lying, and we have long looked for and believed in the symptoms of liars. But the truth is, liars are as varied as the lies they tell. We like to believe we know a liar by their face, by their eyes, by their words, but we have all been blindsided by a lie. It’s something to come to terms with, and it’s something to strongly consider when people’s freedom, and people’s safety, is at stake.