Lie Detector Test Guide

Lie Detector Test Guide

The ancient Chinese had a foolproof method for detecting lies. The person suspected of dishonesty was given a handful of uncooked rice to chew. If it stuck to his mouth or was dry when he spat it out, he was lying. Everyone knew that liars had dry mouths.

Lie detection has come a long way since the “spitting method.”

Modern lie detectors trace back to comic books. William Moulton Marston is best known for creating Wonder Woman, but he also managed to invent the systolic blood pressure test. This test became a major component of the first polygraph lie detector, invented by John Augustus Larson in 1921.

How Do Polygraphs Work?

As a subject answers a series of questions put to him by an examiner, the polygraph records heart rate, blood pressure, breathing and perspiration.

Polygraph machines can’t scientifically detect dishonesty. They can only flag physiological changes, such as heavy sweating or spikes in blood pressure, that often occur when some is telling a lie.

What Happens at a Polygraph Exam?

The subject is first interviewed by the examiner. He’ll explain how the test works and go over the questions to make sure they’re understandable. Some examiners give a short simulation test to demonstrate that the machine is reliable.

The equipment works this way:

  • Thin, inflated tubes called pneumographs are wrapped around the chest and waist to monitor breathing patterns.
  • Blood pressure and heart rate are measured in a blood pressure cuff.
  • A galvanometer measures perspiration by means of electrodes attached to the fingertips.
  • Most modern machines work off computer systems. As the subject answers each question, the computer graphs his physiological responses. The polygraph examiner then reads and assesses the information and makes a determination as to whether or not the subject was answering truthfully. A report is compiled for the person who requested the test.

What Questions Does an Examiner Ask?

Questions are usually patterned after those used in criminal investigations.

The Control Question Test uses three kinds of questions:

  • Irrelevant questions are used as a baseline to establish the normal physiological state of the subject. Usually, they are questions to which the answers are not in dispute, such as “Who is the current U.S. president?”
  • Relevant questions are specifically about the crime being investigated. “Did you rob the bank?” is a relevant question.
  • Comparison questions are broader but are indirectly related to the investigation at hand. “Have you ever behaved dishonestly or stolen anything?” is a comparison question.

In theory, if the suspect is innocent and telling the truth, he will have very little reaction to the point-blank question “Did you rob the bank?” He knows that he didn’t. The comparison questions, however, may set his heart racing. Hardly anyone has gone through life without lying about something or stealing a candy bar.

When reactions to the comparison questions are more dramatic than to the relevant questions, the examiner rules that there is no deception. When reactions to relevant and comparison questions are the same, the results are said to be non-conclusive.

Too Much Information

Another kind of test is used when the police have information that only the guilty party could known—that the murder victim wore orange toe polish, for example.

A Guilty Knowledge Test is a multiple choice exam. One answer contains the “secret” information. As the examiner reads the choices aloud, a guilty suspect is likely to have a strong reaction to the answer that contains supposedly secret information.

Polygraphs are most accurate when the subject believes they’re accurate. Many wrongdoers give full confessions when they’re facing a lie detector test.

Where Else Are Polygraphs Used?

Polygraphs may be used by corporations screening job candidates. Some businesses routinely have workers tested for employee theft. Probation officers may use them to monitor offenders. Sometimes, people suspected of criminal acts request polygraphs to proclaim their innocence and clear their names.

How Much Does a Lie Detector Test Cost?

A single exam costs around $500-1,000. Examiners may set their own fees according to their experience. Hi-tech machines that measure all signs of short-term stress, including changes in vocal pitch and frequency, can cost as high as $10,000.

Voice monitoring equipment is now often sold on its own. The system, which includes a phone adaptor, can be installed on a personal computer. Home versions sell for as little as $150. More complex systems for businesses are available for about $1,000.

Other Types of Lie Detectors

Researchers have come up with other ideas for getting at the truth. Since lie detection is hard to validate scientifically, their experiments with the following have had mixed results:

  • Skin temperature
  • Brain imaging
  • Cardiac output
  • Eye tracking
  • Facial movement
  • Speaking patterns
  • Choice of words
  • Voice testing

Experiments with sodium thiopental and marijuana resulted in most subjects alternating between the facts and bizarre stories. They only worked among subjects who thought it was impossible to lie when under the influence of the drugs.

Why Are Lie Detector Tests Controversial?

Critics have long protested polygraphs on scientific, legal and ethical grounds. They point out that reactions such as excessive perspiration, racing pulse and shallow breathing are not specific to lying. People who are nervous about being hooked up to a machine could react the same way. Someone who is startled or anxious in general may experience sharp increases in blood pressure.

Bias on the part of the examiner, even on a subconscious level, could skew results. Physical fitness, age and certain psychological disorders could affect outcomes. Also, detractors say that polygraphs favor dishonest people; many deceivers study ways to beat the test.

In most courts of law around the world, including the U.S. Supreme Court, polygraph results may not be admitted into evidence.

How to Beat a Lie Detector Test

The jury is still out on whether or not it’s possible to fake your way through a polygraph. People have tried clinching their toes, doing mental arithmetic and biting their tongues. There are drugs, and even foods, that could that could alter physiological responses.

Usually, polygraph examiners are wise to these tricks and discontinue the test. A notation that you attempted to fake results is almost as bad as flunking the exam outright.

Famous Polygraph Cases

Polygraphs have been prominent in several high-profile criminal cases, including:

  • Gary Ridgeway, 1984
    The Green River Killer passed a polygraph during the midst of his savage spree. In 2003, after his DNA was linked to the crimes, he pled guilty to 49 murders. He later confessed that the number of victims could be as high as 90.
  • O. J. Simpson, 1996
    Years after his criminal trial, two of Simpson’s attorneys separately told the media that he failed a polygraph exam days after the murders of his ex-wife and her friend. Simpson hotly disputed their claims.
  • JonBenet Ramsey, 1996
    Jon Benet’s parents, John and Patsy Ramsey, refused to take polygraphs immediately after their daughter’s murder in 1996. However, they volunteered for testing in 2000 and appeared to be telling the truth. In both the Ramsey and Simpson cases, Edward Gelb administered the tests. He was the country’s foremost polygraph examiner at the time.
  • Natalie Wood, 1981
    The actress’s drowning was considered an accident for almost 30 years. In 2008, Dennis Davern, the skipper of the yacht from which she disappeared, came forward. He claimed that Wood’s husband, actor Robert Wagner, had a hand in her death and had sworn him to silence. Davern took several polygraph tests over a few months. Examiners declared that he was telling the truth.
  • Richard Jewell, 1996
    Jewell, chief suspect in the 1996 Atlanta Olympics bombing, was unfairly condemned by the public even after passing a polygraph. Eric Robert Rudolph was later proven to be the bomber.

Once psychologists learn more about the nature of lying, accurate lie detection is a realistic possibility. For now, lie detector tests aren’t perfect, but they’re more reliable than instinct—or the spitting method.

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