The Truth About Lie Detectors

A test subject is wired to a computerized polygraph instrument, also known as a lie detector test.

The Truth About Lie Detectors

Most people tell little white lies at least some of the time. While on average, an adult will tell 1.7 lies each and every day, some people lie a lot!  Because of these chronic liars, the scientific community has been searching for a way to distinguish a lie from the truth, ever since Pinocchio turned into a real boy.

Many people believe they’re really good at spotting liars. Yet, this is just not so. In a study led by Dr. Alder Vrij, a noted researcher from the University of Portsmouth, “When detecting deceit via nonverbal cues, accuracy rates (percentage of correct answers) usually vary between 45 to 60 percent…”. Simply put, human beings are not really very good at distinguishing the truth from a lie; they just think they are.

Polygraph examination, better known as lie detector testing, is the science of finding the truth. Whether used by law enforcement agencies or in the private investigation sector, the fact is that detecting lies is far more complex than most people know.

Two men greet each other with a handshake, while the man on the right crosses the fingers of his left had behind his back.

History of Lie Detectors

While there have been earlier variations, the modern lie detector machine was developed by John A. Larson in 1921. Larson, a Canadian psychologist then working with the Berkley, California police department, developed a machine that would continuously measure and record a subject’s heart rate, blood pressure and breathing, all at the same time.

He named his creation ‘polygraph’, a Greek reference to multiple (poly), and writings (graph). The Berkley police chief at the time saw the value of Larson’s machine while conducting suspect interviews in criminal interrogations. He allowed Larson to refine his polygraph instrument during actual police investigations.

An assistant to Larson, Leonard Keeler, went on to develop and refine structured procedures for administering a modern lie detector test, focusing on questioning technique. Keeler also made the equipment portable, and eventually added a channel to measure a subject’s perspiration. This last measure for sweating proved to be a highly effective refinement to the equipment.

It’s mainly these functions, the ones over which we have no active control, which can be used to judge deception during a polygraph test.

While his predecessors were mostly interested in academic research in detecting lies, Keeler recognized the commercial value of conducting polygraph examinations. Keeler went on to secure a patent for his polygraph machine and founded a school for training others in the science of polygraph examination.

How a Lie Detector Works

Early polygraph machines used pens attached to drums in order to record physiological reactions. These created visible patterns on a role of paper advancing mechanically through the machine. While today’s computerized equipment provides the operator with completely digital data, the basic operation of lie detector equipment remains the same. A polygraph machine measures heart rate, breathing and sweating.

How People Respond to Stress

The human body is remarkably complex. While everyone has control over some of their bodily functions like when we eat, drink, sleep or wake-up, there are also functions over which we have no control. It’s mainly these functions, the ones over which we have no active control, which can be used to judge deception during a polygraph test.

Blood Pressure

The body continuously manages blood flow in order to sustain life and to perform regular activities. A person’s resting heart rate and blood pressure is increased or decreased through the release of certain chemicals triggered by the nervous system. Some factors which affect blood pressure and heart rate include the perception of a threat. 

While conducting a polygraph exam, the polygraph machine will rely on a standard blood pressure cuff to continuously monitor the subject while being asked a series of questions.

A test subject undergoes a polygraph exam.

Breathing Rate

Except when we try to force it, we usually have little to no control over the way we breath. Breathing regulates the level of oxygen and carbon dioxide in the body, and is controlled by our nervous system. The nervous system affects how deep a breath we take and how often.

Because a test subject could try to defeat the machine by trying to control breathing, most examiners attach sensors to the subject in order to detect irregular breathing patterns. During the exam, breathing is measured using an apparatus positioned around the subject’s middle. This device allows the examiner to precisely measure breathing patterns. Thus, irregular patterns can easily be detected.


Most polygraph machines will measure the subject’s level of perspiration by attaching two electrodes to the subject’s fingers or hand, and passing a tiny current between them. This measure is referred to as the galvanic skin response, or GSR. Many consider this to be the most effective measurement in lie detection.

The reason has to do with adrenalin. Emotional arousal from stress can affect our adrenalin level, which in turn affects our breathing, and blood pressure. Yet, adrenalin does not affect a subject’s level of perspiration. It is for this reason that GSR is considered to be more accurate in detecting deception than either breathing or heart rate.

Countermeasures to Defeat the Lie Detector

Any test subject who has ever thought of ‘beating’ a polygraph exam has probably searched for advice online. They probably read some clever posts about self-inflicting pain while answering control questions in order to generate an elevated physiological response. This can be done by pressing a toe against a thumbtack placed inside a shoe, or biting your tongue or inside of the cheek. He might try to accomplish the same result by learning to clench his butt muscles when asked to answer a question.

The fact is that polygraph examiners are well trained to spot the tricks used by someone trying to beat the test. They’re actually looking for signs of deceptive activity, not just deceptive answers when someone lies in response to a question. Besides, most modern polygraph machines are designed to make cheating ineffective, if not downright impossible.

For example, most polygraphs include sensors like seat pads, arm rest pads and neck pads to detect unnatural movement when answering a control question. These movements can affect readings when answering a relevant question. A subject is also instructed to remove his shoes at the start of the test, just in case.

Most experienced examiners don’t even need these sensors to spot irregular activity. Remember, a subject usually takes only one polygraph exam in his entire life. An experienced examiner will have conducted hundreds, if not thousands of thorough examinations before this one. The examiner will quickly spot someone trying to cheat the test — and won’t be shy about including those facts in a report summarizing the polygraph results.

Franco Investigation Services Ltd. offers confidential polygraph services for criminal, civil and domestic cases. Contact us today for a consultation.