polygraph exam

Do lie detectors actually work?

A deception detection expert’s account of the polygraph exam

Feeling Gratitude

Is it called a lie detector or a polygraph?

First created in 1921 by a law enforcement officer, the polygraph machine’s sole purpose was to track moment-to-moment physiological changes in a person’s blood pressure, heart rate and respiration as proof of deception. Today, we know that polygraphs are not the lie detectors that we trusted them to be. Unfortunately, that still doesn’t prevent the common albeit incorrect belief that a ‘lie detector’ and ‘polygraph’ are the same.

If there are no universal signals for deception, then it should come as no surprise that there are no fool-proof methods to determine if or when a person is lying; at least, not without requiring the use of additional tools and techniques to investigate further. The polygraph lie detector works on the same principles as detecting deception through observing behavioral and physiological signs, and it is vulnerable to the same problems.

Simply put, the polygraph exam doesn’t detect lies, it detects signs of emotion.

What do polygraph machines record?

Before beginning the interview (or interrogation), the set-up is fairly simple: wires connected to the polygraph machine are attached to the subject (or suspect) to measure and record physiological changes. In order to accurately assess and analyze the data collected, it’s imperative to establish a baseline first.

This step is usually performed by asking the interviewee to respond to basic identifying information, answering only with a “yes” or “no” to prevent ambiguity (e.g., “Is your name Joe Smith?”, “Were you born in Juneau, Alaska?”, “Are you currently a manager at X Company?”). By asking them to simply confirm or deny specific questions with answers already known to the interviewer, any increases or decreases in the amount or rate of perspiration, respiration, and blood pressure can be identified.

However, increases in blood pressure or sweating are not, in and of themselves, signs of deception! Hands get clammy when we’re nervous, and hearts beat faster when our emotions are aroused and the stakes are high.

What is a Stim Test Polygraph?

Before giving the polygraph test, most polygraph operators try to convince the suspect that the polygraph never fails, giving what is known as a “stimulation,” or “stim,” test. The most common technique is to demonstrate to the suspect that the machine will be able to tell which card the suspect picks from a deck. After the suspect has picked a card and returned it to the deck, he is asked to say “no” each time the polygraph operator asks him if “this” was the the card originally picked. They justify lying to the suspect on two grounds: If innocent, it’s important that he thinks the machine makes no mistakes. If he is guilty, it is important to make him afraid of being caught.

Most polygraph operators don’t engage in deceit, but instead rely upon the polygraph record to spot which card was taken. For those using this technique, however, it’s vital that no mistakes are made. This leads some interviewers to increase their control over the environment, sometimes opting to use a secretly-marked set of cards, essentially relieving the polygraph from having to perform any real deception detection. Especially in instances like these, polygraphs can quickly lose their integrity as a way to study an individual’s behaviors, independently and without biases; otherwise, they’re just another tool used to strengthen one’s confidence in the data collected.

Where Polygraph Exams Fall Short

The suspect must believe in the ability of the lie catcher. Signs of fear would be ambiguous unless matters can be arranged so that only the liar, not the truth teller, will be afraid. The polygraph exams fail not only because some innocents still fear being falsely accused or for other reasons are upset when tested, but also because some criminals don’t believe in the magic of the machine. They know they can get away with it, and if they know it, they are more likely to be able to do so.

Some polygraph operators attempt to extract a confession by convincing their suspects that they can’t beat the machine. When a suspect does not confess, some polygraph operators will browbeat the suspect, telling the suspect that the machine has shown that the suspect is not telling the truth. By increasing detection apprehension, the hope is to make the guilty confess. The innocent suffer the false accusations but supposedly will be vindicated. Unfortunately, under such pressures some innocents will confess in order to obtain relief.

Learn How to Detect Lies through Micro Expressions

Anyone can learn how to spot deception. Read more about micro expressions, the facial expressions revealing someone’s true emotions.

Paul Ekman is a well-known psychologist and co-discoverer of micro expressions. He was named one of the 100 most influential people in the world by TIME magazine in 2009. He has worked with many government agencies, domestic and abroad. Dr. Ekman has compiled over 50 years of his research to create comprehensive training tools to read the hidden emotions of those around you.

Comments 3

  1. There are several things to consider regarding polygraphs and Voice Stress Analyzations: They are good at detecting stress! Many things can cause stress. For example, if the examiner asks the subjects about theft, the subject may be innocent of the theft, but may be reminded of an incident in which they know someone who committed a theft, and can show stress in their answer. An astute examiner has to take such things into account when formulating the questions. In fact, the results of the polygraph are so often really inconclusive that the results of a polygraph test are inadmissible in court. When administering a polygraph examination, this fact must be borne in mind. One of the main things to remember is that the answers can be used to generate more questions! Most examiners are not as well trained in this as they should be. The other thing to bear in mind is that very oftenly people who have NPD (Narcissistic Personality Disorder – about 25% of the population) are a form of sociopath and/or a psychopath. They can lie like a rug and never show any signs of stress whatsoever.

    1. While I agree with the first half of what you said, I must point out that NPD is not nearly as common as you suggest. 1% or less of people have it. Also, you seem to suggest a connection between sociopaths/psychopaths and NPD. As far as I know, these are two completely different disorders. Antisocial Personality Disorder is the DSM category for what is commonly called psychopath.
      Moreover, to my best knowledge, while people with ASPD are capable of traceless lying (due to their lack — or perverted nature — of conscience), people with NPD lie, but not without traces (especially because they are frustrated).

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