How to cheat a lie detector? How accurate are the polygraph tests?
In November 1985, when Mark Hofmann walked into the office of University of Utah Professor Charles Honts, he seemed calm and relaxed. Hofmann came to take a polygraph test.
Hofmann was asked about his involvement in the murders of Steve Christensen and an elderly woman, Kathy Sheets. Hofmann maintained that he was innocent, and successfully passed a lie detector test.
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In fact, Hofmann was guilty of both murders, as well as dozens of other crimes, including forgery. After Hofmann was convicted of murder, Honts visited him in prison and asked him how he had tricked a lie detector.
Hofmann replied that, anticipating such a test, he bought a blood pressure monitor and practiced with it until he learned to control his blood pressure. Hofmann also said that he practiced self-hypnosis and was able to hypnotize himself to believe that he was innocent.
In addition, psychopaths and sociopaths do not have the same physiological responses to lying as ordinary people, and their guilt is difficult to detect on a polygraph.
With the help of a polygraph, certain physiological characteristics are measured and recorded, including blood pressure, pulse, and respiratory rate, while the person is asked questions. It is assumed that lying causes physiological changes, such as increased blood pressure, increased pulse and respiration, and increased perspiration.
Invention of lie detector
The polygraph was adapted for forensic examinations in 1921 by John August Larson, who at the time had a Ph. D. in physiology and was working as a police officer. Larson first invented this device many years ago as a medical student at the University of California, Berkeley. Larson’s protege, Leonard Keeler, added a perspiration detector to the device in 1939, and then sold the device to the U.S. Federal Bureau of Investigation.
The lie detector consists of two pneumographs, which are rubber tubes filled with air. They are fixed around the subject’s chest and abdomen to measure the breathing rate. The cuff for measuring blood pressure is put on the forearm. Two plates of the galvanometer are placed on the test subject’s fingertips to measure sweat production.
Today, the old analog polygraphs that we used to see in movies have been replaced by computers. Polygraphs are used by the FBI, the FSB, the National Security Agency (NSA), and the Central Intelligence Agency (CIA) when making hiring decisions. Some police departments also use a polygraph to screen new employees.
How accurate are the polygraph tests?
In 2003, the National Academy of Sciences of the United States concluded that the accuracy of the polygraph in identifying real or potential violators of law and order is insufficient to justify its use in checking the safety of employees in federal agencies.”
The report of the Moynihan Commission on State Secrets to the US Congress concluded that”…the polygraph is neither scientifically sound nor particularly effective, apart from its ability to gain recognition.”
In 1986, CIA officer and KGB spy Aldrich Ames was tested on a polygraph. He turned to his Soviet instructor for advice on how to bypass the lie detector, and got a simple tip: “Get a good night’s sleep, rest, and go to the test relaxed. Be friendly with the polygraph operator, express your willingness to cooperate and try to remain calm.”
Ames easily passed this test and another in 1991. Ames said, “ There is no special magic … Confidence is what will help you. Trust and friendship with the examiner … mutual understanding when you smile and he thinks that you like him.”
How to bypass the lie detector on testing
A commonly accepted tactic of cheating the polygraph is to carefully control your breathing and artificially increase your heart rate during control questions. These include questions that people are more likely to lie about, such as: “Have you ever stolen money? Have you ever lied to your parents? Have you ever cheated on an examiner on a test? Have you ever picked up something valuable at work?”
If you lie when answering these questions and intentionally cause pain, such as biting your tongue hard, or if you force yourself to do complex mathematical calculations in your head, you are likely to increase your blood pressure, heart rate, breathing, and sweat volume, and the polygraph examiner is likely to explain your reaction by lying.
If you then lie when answering a normal question, and your body’s response is weaker than to the control questions, your answer will be interpreted as true.
Printers, knowing about such tricks, may ask to take off their shoes, because the subjects may hide sharp buttons in them.
Another tactic you can use to beat the lie detector is to force yourself to think about something pleasant. This will relax you and hide the lie from the detector.
