If you could know when someone is lying, wouldn't it be amazing? Unfortunately, polygraph machines and other traditional lie detection techniques are no more reliable than chance. The circulatory, respiratory, and electro dermal activities of a person may be precisely monitored by a polygraph machine, but it cannot tell if the individual is lying.
A Brief Overview of Lie Detection Methods
Hypnosis, employed in an official capacity since the 1840s, was one of the earliest techniques for detecting lies. Under hypnosis, practitioners thought that people would be more honest in this vulnerable (and suggestible) condition, which is seen as a state of artificially induced slumber. In addition to the technique's dubious ethics, the results were not trustworthy.
When scopolamine, sometimes known as "twilight sleep," was given to patients in the 1910s, a doctor observed that it caused them to divulge personal information. This gave rise to the area of narcoanalysis, when barbiturates such as sodium amytal and sodium pentothal were given to people while they were being questioned as "truth serum." This method was based on the idea that psychoactive substances make people more open and honest by lowering their barriers. While some narcoanalysis techniques are still used today, most developed democracies do not.
History of the Lie Detector Test
John A. Larson, a California police officer, invented the polygraph, sometimes referred to as the lie detector, in 1921. It was an apparatus that could simultaneously track variations in blood pressure, respiration, and heart rate. The device's operation can be linked to two previous advancements:
- Italian psychologist Vittorio Benussi's research on the effects of laying on breathing was published in 1914 under the title Die Atmungssymptome der Lüge.
- William M. Marston, an American psychologist, developed a discontinuous systolic blood pressure test in 1915 to identify dishonesty.
Larson used actual cases in his precinct to test his gadget and processes, but Leonarde Keeler, his protégé, improved the testing methods, made the device portable, and included a feature that could measure the subject's galvanic skin reaction.
Putting Lie Detectors on Trial
William M. Marston attempted to have the results of a lie detector test admitted as evidence in a
court of law in 1923 in what would turn out to be the landmark case United States v. Frye. A
precedent for the admission of testimony from experts in U.S. courts for years to come was set
once the court rejected the lie detector results, establishing the Frye standard.
More
than 40 years later, in 1965, the United States Committee on Government Operations conducted the
first empirical analysis of the polygraph testing apparatus and came to the harsh conclusion
that it was ineffective in detecting fraud, as was pointed out at the beginning of this article.
Despite the committee's decision, proponents of the lie detector test were still moving forward
at full speed at this point. In 1983, then-President Ronald Reagan of the United States released
National Security Decision Directive 84, which permitted the use of polygraphs by federal
organizations. This was another significant change. In an intriguing (and unpleasant)
development, the president revoked the decree three months later due to the Office of Technology
Assessment's unfavorable evaluation of the approach.
The Basic Science Behind Polygraph Tests
Three physiological reactions that are frequently connected to dishonesty are monitored during polygraph tests:
- Cardiovascular activity
- Respiratory activity
- Electrodermal activity
Cardiovascular Activity
Activities frequently linked to lying, such as responding to a perceived or expected threat ("fight or flight" reaction) and increased mental activity, can have an impact on blood pressure, heart rate and other cardiovascular processes. Similar to those used in medical settings, polygraphs employ a wrist, arm, or finger cuff with a sphygmomanometer to assess cardiovascular activity.
Another way to measure cardiovascular function is with photoelectric plethysmographs, which are worn on the subject's ear or finger use infrared light to enter tissue. The light that is reflected or passes through the tissue is then measured by photosensors. The quantity of blood it traveled through before arriving at the sensor is directly tied to this. This eliminates the requirement for a pressure cuff and allows the practitioner to measure variations in blood volume.
Respiratory Activity
Although breathing may be readily regulated by the central nervous system, changes in respiratory
activity are also considered to be a sign of dishonesty, albeit this test is considered to be
less accurate.
Pneumatic rubber bellows are fastened to the subject's belly and thorax to
assess respiratory activity. Changes in the abdominal and thoracic circumference are caused by
the bellows expanding with inhalation and exhale. The internal pressure is monitored using a
pressure transducer..
Electrodermal Activity
Electrodermal activity measurement is regarded as the most sensitive and accurate of the three methods. Why? The sympathetic nervous system regulates the eccirine glands, which produce perspiration and are primarily responsible for the electrical resistance and conductance of the skin. Two electrodes are affixed to the subject's fingers or palm in order to assess electrodermal activity. By applying a little current, the conductance level and any changes in the skin are measured, along with the frequency of spontaneous reactions, the amplitude of event-related responses, and several other variables.
Detecting Deception, Deceiving Results
A line graph with three values representing the respiratory, cardiovascular, and electrodermal outcomes shows the polygraph's real-time physiological reactions. But can the physiological findings be used to answer the psychological question of whether the patient is lying or not? That is debatable.
The fact that physiological reactions to the test can vary greatly between people, or even the same person in various situations, is one of the primary problems with the accuracy of polygraph tests. Furthermore, a person's heart rate and galvanic skin reaction can be impacted by changes in their respiration. Even these physiological reactions may be somewhat controlled by those who practice mindfulness and breathing methods (usually for stress management, not so they can be as misleading as possible!).
According to a 2006
study, the average accuracy of polygraph testing is 54%, which is just over chance.
What alternatives are there for identifying dishonesty if polygraph testing are
unreliable? Advanced interrogation tactics are frequently employed by law enforcement and
criminal justice professionals, when the polygraph is not utilized as a tried-and-true lie
detector but rather as a psychological tool to help the interrogator. Some very skilled
interrogators even focus on nonverbal clues and facial microexpressions. Even if these methods
are difficult to measure, the investigators' intuition may be far more trustworthy than
"chance."
Conclusion
Polygraph tests have long captured public imagination as scientific tools for exposing deception, yet their reliability remains highly questionable. While they can measure physiological signals such as heart rate, breathing, and skin conductance with precision, these indicators reflect stress or arousal rather than lies themselves. Individual differences, situational factors, and even deliberate control of physiological responses make the results inconsistent at best. With accuracy levels hovering only slightly above chance, polygraphs are far from the foolproof detectors they are often portrayed to be. Today, they serve more as psychological aids in interrogation than as definitive evidence of truth or falsehood. Ultimately, detecting deception continues to rely less on machines and more on human judgment, careful questioning, and subtle behavioral analysis.