Question of the Week

Could some people pass a lie detector?

Sun, 30th Nov 2008

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Brian Kennedy, N Yorks asked:

Would someone with a psychiatric disorder be better able to pass a lie detector test as they may not feel remorse?


We put this to Jim O’Shea, Intelligent Systems Group, Manchester Metropolitan University:

PolygraphOld-fashioned lie detectors like the polygraph only detect stress. If the lack of remorse meant that the interviewees had reduced stress levels that would help them pass. Our lie detector, Silent Talker, makes its judgement on non-verbal behaviour: crudely what people call body language. Silent Talker can detect stress but lying involves other factors. We can only juggle a certain number of mental variables at once while we’re thinking. If we’ve got to try and maintain a whole load of different factors about an imaginary story it’s very difficult to do all the mental processing to keep that consistent. That’s what’s known as having a high cognitive load which affects non-verbal behaviour. Also duping delight occurs when liars get a kick out of getting a lie across successfully and again this affects non-verbal behaviour. In one of our own experiments on the general population we taught silent talk to recognise guilty feelings the participants felt while they were lying. When we added this information to the general lie detection we got more accurate classifications. In another independent study conducted by a different university using Silent Talker it was found that Silent Talker was effective at detecting lies told by psychopaths in interviews. So there we have it: evidence that remorse is a factor in the general population but also evidence that in the case of one disorder it’s not the only factor.


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A person with antisocial personality disorder (sociopath) would not feel remorse about committing an offence, but could be anxious about facing the consequences of their actions (e.g. imprisonment), the physiological signs of this anxiety could be detected on a polygraph (lie-detector) .

A person with a psychiatric disorder which included amnesia may not recall committing the offence, so would be less likely than the sociopath to show physiological signs of anxiety when questioned. RD, Tue, 25th Nov 2008

Disorders that manifest delusions may be advantageous to overcoming a polygraph. JnA, Wed, 26th Nov 2008

I'm sure that it's possible to train yourself to deceive a lie detector test.

C chris, Thu, 27th Nov 2008

yes, some people can manipulate normally 'automatic responses' like blood pressure and pulse. I believe the most difficult automatic control to 'manually control' is the pupil, don't they use that as an indicator of a 'real winner' in Vegas? JnA, Thu, 27th Nov 2008

They have tested this with people that done especially savage and disgusting crimes.
Some of them with brain damage (frontal lobe?) didn't have any remorse at all.

And to make a lie detector react you need to know/understand that you're in the wrong.
Try to give the test to some dog that just shit down your back yard:)

Could that be why politicans are so convincing;)
They make themselves believe what they say::))

Medicines have also been used to fool lie detectors. yor_on, Sun, 30th Nov 2008

like medicines that lower blood pressure etc? How does it fool the polygraph?
The suspect is usually asked a series of 'known' questions to establish the base line (which is individual) Even if one was taking meds, the machine would still read activity *if* the person could not manipulate their pulse etc by other means. JnA, Sun, 30th Nov 2008

It's actually very easy to fool lie detector tests. I've done it countless times. I'm not sure I should disclose how. DoctorBeaver, Wed, 24th Dec 2008

There has been a recent Swedish research in which they have tested different lie detecting techniques. All failed:) What is true is more like that samurai movie. Where, if four people, there will be four versions.. And this problem is an important one. Yoron, Fri, 30th Jan 2009

An Israeli manufacturer of lie detectors has threatened to sue researchers from two Swedish universities who collaborated on a study concluding that lie detector tests are useless.

About a year ago, Francisco Lacerda, a professor of phonetics at Stockholm University and Anders Eriksson, a professor of phonetics at the University of Gothenburg, published an article in the International Journal of Speech Language and the Law entitled "Charlatanry in forensic speech science".

In the article, which provided an overview of the last fifty years of research on lie detectors, the two found that there is no scientific evidence proving that lie detectors actually work, reports the Dagens Nyheter newspaper (DN).

When Nemesysco Limited, an Israeli company which produces lie detecting equipment, caught wind of the story, the firm contacted Equinox, the journal’s British publisher, and demanded the article be withdrawn.

Equinox relented, leaving only an abstract of the study on the journal’s website, along with a clarification.

Nemesysco’s reaction troubled the researchers, adding that, in its letter to Equinox, the company also threatened to sue the authors themselves if they continued to publish on the subject.

“It is incredibly serious that they are trying to silence us in this way. I have never heard of anything like it. We have apparently damaged their business," Lacerda told DN

Lacerda explained that his work with Eriksson took direct aim at the company’s lie detector patent.

"We showed that the invention cannot work. The article had a journalistic tone and was rather provocatively written. We wanted to prove that the technology behind the lie detector is a scam," he said.

Nemesysco has also sent a letter to DN claiming that Eriksson and Lacerda have slandered the company.

"It's obviously very uncomfortable,” said Lacerda.

“We don't know where this may end. At the same time, it is my responsibility as a researcher to share my findings. The company has not put forward any counter arguments, but has chosen to simply try to silence us.”

Lacerda continues to closely examine Nemesysco’s patent and wants to publish the results of his findings, either on his own blog or in a scientific journal to ensure the public is made aware of the technology used in lie detector tests.

Ironically, the company’s threat has resulted in a windfall of publicity for the researchers.

“That was probably not their intention. But since the article was removed I’ve received huge quantities of mail and request for copies of the article. It would have hardly been as widely read had the company simply passed over it in silence,” he told DN., Fri, 30th Jan 2009

If Nemesysco don't like it, they should publish research showing that their contracptions work not just try to silence the researchers. DoctorBeaver, Sat, 31st Jan 2009

Tut-tut Nemesysco. Chemistry4me, Sat, 31st Jan 2009

My ex-husband sexually abused my daughter and admitted it to me after I found out. We even took pictures of the bite marks he left on her. Yet, he has managed to pass a lie detector test. How is something like that possible? Troubled, Fri, 27th Feb 2009

My husband passed a lie detector test when I thought he was cheating. There were huge red flags and I've had some confessions also, which he then says are not true and he is saying it cause that is what I want to hear. My instincts tell me he did cheat, those confessions were some what truthful and so therefore, these lie detector tess don't work. I truly believe my husband may be a sociopath also. He never shows emotion. Disillusioned, Tue, 16th Mar 2010

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