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Critical thinker John Turnbull straps into the sphygmomanometer and investigates the polygraph — can this mysterious machine really tell when you’re lying?

IF YOU'VE EVER WATCHED an episode of police procedural dramas, like Law & Order, Blue Bloods or CSI, there’s a good chance that you’ve heard one of the characters order a polygraph test to prove that a suspect is lying. The perp then gets hooked up to an fancy etch-a-sketch machine and asked a bunch of questions, after which a character wearing glasses (and therefore a scientist) glances at the printout and confidently declares “he’s lying!”

With the good fortune of never being arrested for a capital crime, I’ve long wondered whether polygraph machines were accurate — and if they are, how hard is it to fool one?

A Little History

Contrary to what many people believe, the polygraph machine was not invented by William Moulton Marston, the creator of Wonder Woman — although one key component was: the systolic blood pressure test. The polygraph machine was actually invented by John Augustus Larson, the first American police officer to hold a doctorate.

Larson introduced the polygraph to the Berkley Police Department in 1921, and was used to interrogate William Hightower, suspected of the murder of a priest in San Francisco. Analysis of the polygraph results indicated Hightower was lying and he was eventually convicted to life in prison. It’s interesting to note that later in life Larson expressed regret for inventing the device, citing extensive misuse by police departments for his change in opinion.

How do polygraphs work?

From the American Psychological Association:

'The instrument typically used to conduct polygraph tests consists of a physiological recorder that assesses three indicators of autonomic arousal: heart rate/blood pressure, respiration, and skin conductivity. Most examiners today use computerized recording systems. Rate and depth of respiration are measured by pneumographs wrapped around a subject's chest. Cardiovascular activity is assessed by a blood pressure cuff. Skin conductivity (called the galvanic skin or electrodermal response) is measured through electrodes attached to a subject's fingertips.'

It’s then up to an analyst to compare subject reactions between control questions where they expect you to lie – such as: "Have you ever betrayed someone that trusted you?" – and your responses to more pertinent questions, like “Did you kill your wife?”

To illustrate:

'A person who is telling the truth is assumed to fear control questions more than relevant questions. This is because control questions are designed to arouse a subject's concern about their past truthfulness, while relevant questions ask about a crime they know they did not commit. A pattern of greater physiological response to relevant questions than to control questions leads to a diagnosis of "deception." Greater response to control questions leads to a judgment of nondeception. If no difference is found between relevant and control questions, the test result is considered "inconclusive.'

Proponents of the technology – often those trying to sell it to law enforcement – claim 90 per cent accuracy, however this figure is highly contested.

Can you beat a polygraph?

Oh yeah, totally. It’s also very easy to fail a polygraph — even if you’re innocent.

The reason for this is that polygraphs basically reflect how nervous you are. If you’re being interrogated by a couple of experienced police officers in a room designed to be intimidating, I imagine it would be hard not to be nervous, even if you didn’t do anything wrong. The idea that you’ll suddenly relax when you realise that they’ve got the wrong person is fallacious, especially given it has become increasingly difficult in recent years to overturn a wrongful conviction.

Many experts in the field suggest the way to beat the polygraph is simply to relax, which is probably why serial criminals like the Green River Killer, Gary Ridgway, passed multiple polygraphs with flying colours.

Others suggest it’s all about what you do with your anal sphincter, but if you really want to go down that road then, well... knock yourself out.

Inadmissible in court

From an official perspective, polygraph results are not admissible as evidence in Australian courts.

Taking this into account, Advanced Polygraph Australia point out:

'In Australia the results of polygraph examinations may be admissible in any administrative tribunal (ie anti-discrimination tribunal, VCAT) where the rules of evidence do not apply. In criminal and family court law matters, polygraph results may be accepted by the court only in circumstances where the evidence of the polygraph examination is accepted into admission into evidence by all parties to the proceeding.'

So that’s not great.

So why do so many still believe in polygraphs?

Aside from their prevalence in popular culture, polygraphs remain popular in some circles due to their intimidating nature. If you’re applying for a job at the CIA or NSA, for instance, it’s probably handy for your prospective employer to know if you’re prone to cracking under pressure.

Aside from that, polygraphs are just another form of intimidation used by law enforcement. Like an electronic version of good cop/bad cop, a polygraph can be used to exert psychological leverage: “The polygraph proves that you’re lying. You might as well confess.”

At the end of the day, polygraphs are pre-scientific nonsense that evidently still has a role to play in modern society — just don’t believe what you see on TV. 

Think for yourself.

Books by John Turnbull are available on Amazon and Kindle, including supernatural thriller Damnation’s Flame; action/romance Reaper, black comedy City Boy and travel guidebook Bar Trek: EuropeDamnation's Flame by John Turnbull is also available in paperback in the IA store HERE (free postage).

Creative Commons Licence
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Australia License

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