The Pseudoscience of Lie Detectors

More commonly known as the lie detector, the polygraph is a device that measures the changes in our nervous systems, detecting and recording heart rate, respiration, sweating and blood pressure. It allegedly operates on the premise that due to anxiety and fear, people produce involuntary physiological responses when they lie. Some claim that polygraph testing is up to 96% accurate, while others claim 50%, but it’s likely somewhere in between. Polygraphs only detect physiological responses, which don’t directly translate to proof of lying—some guilty people can remain completely calm while lying, while innocent people might produce ‘guilty’ responses. Polygraphers ask control questions to determine normal responses and balance this, but the tests are therefore inherently subjective because a human interprets the results. The ‘base rate fallacy’ also causes considerable problems, involving ignoring statistical information and not taking into account the frequency of what’s being tested for. For example: using the 96% accuracy rate, suppose that statistically, 1 in 10,000 people are terrorists—but if 10,000 people are randomly polygraphed, 1 terrorist and 400 false positives will be turned up, so the 96% accuracy isn’t useful or meaningful. Polygraphs are used as a tool for psychological bullying rather than accuracy, intimidating suspects into confessing—and they are, therefore, a pseudoscience.

Linguists: creating better polygraph tests?

This paper by Newman, Pennebaker, Berry and Richards examines some linguistic style features that can tell apart true and false stories with a fairly high degree of accuracy. Abstract: 

Telling lies often requires creating a story about an experience or attitude that does not exist. As a result, false stories may be qualitatively different from true stories. The current project investigated the features of linguistic style that distinguish between true and false stories. In an analysis of five independent samples, a computer-based text analysis program correctly classified liars and truth-tellers at a rate of 67% when the topic was constant and a rate of 61% overall. Compared to truth-tellers, liars showed lower cognitive complexity, used fewer self-references and other-references, and used more negative emotion words.

There’s definitely a lot of room to be wrong, so I doubt we’ll see this technique in court any time soon, but it’s significantly better than predicted by random guessing, so maybe it’ll eventually get there! 

A polygraph (lie detector) records changes in heart rate, blood pressure, breathing, and the the galvanic skin response. The galvanic skin response is recorded from the hand by electrodes that measure skin conduction, or more simply, sweating. “Polygraph” means many writings and was invented by the psychologist William Marston in 1915. 


Drawing the news with digg: How To Tell If Someone Is Lying To You


How Do Polygraph Machines Work?

Also known as ‘lie detectors,’ polygraphs are used to record an individual’s vital signs, such as breathing rate, pulse, and so forth. Check out this episode of BrainStuff to learn more about polygraphs and the art of lie detection.


The money I would fucking pay to see Cursed just once in my life.

I’ll also take this moment to give a giant fuck you to the assholes who robbed them in Amsterdam which inevitably led to their demise. FUCK YOU.

Lie Detectors- Proving Liars or Proven Liars?

Lie detectors, or polygraphs, are used to measure changes of breathing, perspiration, and heart rate.  The accused is first asked a control question, designed to make the suspect a little nervous and cause arousal that the polygraph would detect.  Later, they are asked the relevant question and if this provokes a greater reaction, the accused is proclaimed guilty.  If the relevant question provokes a lesser reaction, it is safe to say the person is telling the truth.  If this system is so straightforward, why don’t we use it all the time?  The truth is, it is very easy for an innocent person to look guilty when taking a lie detector test.  It is psychologically proven that the fear of being disbelieved while telling the truth looks a lot like the fear of being caught lying.  Most often, the jury is not aware of this and only focuses on the results of the polygraph when making their decisions.  When this happens, the innocent is voted guilty and prosecuted for a crime they did not commit.

lloyfid asked:

Interesting fact: One of the creators of Wonder Woman, William Moulton Marston, also invented the lie detector test.

He was also polyamorous (living with two women in a “surprisingly harmonious” [as per his biographers] relationship for most of his life), and a fairly strong feminist relatively pro-female figure, at least for his time.

I hate the term “lie detector test” when it comes to polygraphs; they’re not even reliable enough to be used in US courts, and we allow a LOT of questionable science in. But they’re still used for intimidation and coercion by police departments with very little oversight. :\ But yes, he did! And I commend him for recognizing a LOT of the weaknesses of the machine from the get-go, even if he wasn’t actually listened to beyond “this MIGHT help you catch SOME liars!”