Does Lie Detector Really Work?


The lie detector, once thought to be a powerful tool for truth telling, has been debunked many times. Yet, it still appears at “pressure-cooker” political moments, when governments lower their requirements for scientific rigour, says historian Ken Alder.

Police departments use it to investigate crime, and the CIA, FBI and other government agencies demand it of people seeking security clearances. It’s also used to monitor sex offenders on probation and parole.

The History

When it comes to polygraphs there is a very long and rich history of research, study and learning. The premise behind these tests is that the act of deception causes a number of different physiological responses.

These changes can be picked up by a polygraph machine and interpreted by the examiner. The test itself is very much like any other interview, with the exception that only the questioner and the person being questioned are present. This ensures that there is no emotional or personal influence, bias or the subject feeling watched over and unable to talk freely. Get more info on this Lie Detector Test website.

The very first polygraph machines were developed in the early decades of the 20th century. These used the same technology as a blood pressure monitor and could measure a subject’s galvanic skin response (a proxy for sweating), breathing rate and blood pressure. Despite the fact that they were 19th century technology, these tests are still routinely used by government agencies and law enforcement.

The Science

For as long as they’ve been around, liar-detection machines have been accused of being unreliable. Despite the fact that their results can’t be used in court, police departments and intelligence agencies have snapped up the devices to help them investigate suspects. Companies like Converus offer software that analyses a subject’s eye movements and pupil dilation, while others have tried to boost accuracy by incorporating cameras or even brain scanning.

One theory is that liars exhibit typical stress responses, including an increase in heart rate and blood pressure, but truth tellers don’t. This can make a polygraph machine appear to be accurate, but it also can present innocent people as guilty.

Other research has found that human lie detection is pretty ineffective, with a 50 percent chance of a correct judgment (which means that guessing correctly would yield the same result). And studies have also shown that professional “lie catchers” are no better than anyone else at discerning deception.

The Methods

A number of people have put forward various devices that claim to detect when someone is lying. Most of these have relied on recording different physiological responses to questions. The theory is that if you’re telling the truth your heart rate should remain stable, but if you’re lying your heart will race and other reactions will take place.

These tests, known as polygraphs, record your body’s responses to a series of questions. The examiner then compares these responses to the relevant ones. The idea is that if you’re lying the answers to the control questions will be higher than the core questions.

However, the accuracy of a polygraph depends on the skill of the examiner. You could have the best lie detector equipment in the world, but if the examiner is rubbish then you’ll never pass your test. There are also ways to skew the results, such as doing yogic breathing or putting a nail in your shoe.

The Results

The polygraph machine—a relic of 19th-century technology beloved by daytime TV hosts and police procedurals—is a pseudoscientific tool that can be misleading or even inaccurate. A polygraph is only as good as the examiner, and even if an examiner is well-trained and ethical, the tests are not foolproof.

The theory behind lie detection is that a person who lies will exhibit specific symptoms like increased heart rate, blood pressure, respiration and sweating, which can be measured by machines. The problem is, innocent people may also display these same physiological responses because they are anxious about taking the test.

In fact, Littlefield and other researchers have shown that a person can pass a polygraph test with no signs of lying by using a controlled scenario, such as being asked control questions and then questions about a crime the subject didn’t commit. This demonstrates that the stress of the questioning is what is really making the test results different, and not whether or not someone is telling the truth.