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How Truthful Are Lie Detectors?

On Behalf of | Aug 12, 2019 | Criminal Defense

From the moment that John Augustus Larson invented the lie detector in 1921, the device has had more than its share of scrutiny and outright controversy. With fine-tuning from protégé Leaonarde Keeler, the University of California-Berkeley medical student Berkeley Police Department officer patented it on January 13, 1931.

The Federal Bureau of Investigation (FBI) eventually purchased the prototype of what would become the modern-day polygraph. Initially, it was used by the CIA to determine the truthfulness of applicants and existing employees. However, it was the McCarthyism era that gave the lie detector prominence.

Vastly Differing Views on Polygraph Tests

Polygraph measurements are determined by a variety of body responses that include changes in blood pressure, breathing depth, and skin conductivity, also known as sweaty palms. The goal is straightforward: determine if the subject is telling the truth.

Early supporters saw it as objective and fair in weeding out spies and traitors. The CIA considered the use of the polygraph in security screenings as “truly unique and indispensable.” Today, they cite the inability of most individuals to control all the physiological functions simultaneously and the pre-examination that measures reactions to telling lies.

Detractors allege that no proof exists that the measures are remotely reliable in determining if the subject is being elusive. They cite the lack of established standards, if not a precise yardstick when it comes to responses charged by emotions. While many can conceal stress, the source of actual stress coming from either a lie or nervousness lacks reliable methods to differentiate.

Most court jurisdictions side with the skeptics and do not use the data for evidence. States that allow the test results can only do so if both prosecutors and defendants agree. Still, polygraphs remain in use and serve as a subjective arbiter in someone’s guilt or innocence.