Liars beware: new truth test unveiled

Nowhere to hide: Meet The Parents is one of many films that portray lie detector tests.

Scientists claim to have developed the most accurate lie detector yet, by analysing body movements for signs of guilt. But do the ethical pitfalls of truth tests outweigh their benefits?

‘I’m going to ask you some questions, and all you have to do is answer yes or no’, a stony-faced Robert de Niro says to his jittery future son-in-law Ben Stiller in the film Meet the Parents. Stiller has been wired up to a lie detector. As he fumbles his way through the interrogation, the needle on the graph swings wildly, exposing his lies and unearthing his most embarrassing secrets.

It’s a memorable scene from a much-loved film. Yet the lie detector, or polygraph, is not confined to fiction. It is also a staple of real life criminal investigations, particularly in the US.

Despite this, polygraphs are actually fairly unreliable and in Europe their use is rare. A skilled examiner can tell truth from lies only 60% of the time — odds not much better than a random guess.

According to new research, however, this could be about to change. This week, British and Dutch scientists announced a far more accurate test which could be rolled out in police stations within the next ten years.

Until now, polygraph tests have ‘worked’ by recording changes in pulse, blood pressure, sweating and breathing. Higher levels of stress and anxiety supposedly signal a guilty conscience.

The new method will rely instead on monitoring the motions of a person’s whole body. The reasoning behind this is that liars fidget more. So forcing a subject to wear a suit containing 17 sensors that register movement up to 120 times per second in 23 joints should yield more accurate results.

So far, the new method has performed well in tests, with a success rate of over 70%. Yet despite this breakthrough, many experts are adamant that the body cannot be trusted to betray its secrets, and that a 70% success rate still leaves an alarmingly wide margin for error.

They maintain that practiced liars, particularly psychopaths, will always find ways to fool polygraphs, no matter how sophisticated they become, while innocent subjects, naturally nervous under pressure, will be wrongly convicted for crimes they didn’t commit.

Hips don’t lie?

In the 1996 science-fiction novel The Truth Machine, scientists invent a device that can detect lies with perfect accuracy. The result? Crime is abolished and humanity is saved from self-destruction. Many would agree that a world free from lies and uncertainty would be a better place for honest, law-abiding folk.

Some, however, are horrified at the prospect of a dystopian future where machines detect our every deception. Lies come in many shades, they say, from small, white ones to the lies we tell to protect people we love. Everybody has a right to secrecy and ownership of their thoughts. Science must never be allowed to infiltrate the privacy of the mind.

You Decide

  1. Under what circumstances, if any, is lying justifiable?
  2. Would the world become a better place if lying was abolished today?


  1. Get one volunteer in the classroom to make up a false alibi for where they were last Monday evening. In groups, devise a strategy to work out how to prove they are not telling the truth. Can you prove they are lying?
  2. Write a short story about somebody who is forced to choose between revealing a damaging truth or lying.

Some People Say...

“The mouth may lie, but the face it makes nonetheless tells the truth.’Nietzsche”

What do you think?

Q & A

Will I ever have to take a lie detector test?
If you wanted to work for the FBI you would have to take one, as they use polygraphs to vet all employees. If you were wrongly implicated in a criminal investigation you might have to take one too. While a failed lie detector test is not enough to result in a conviction in a UK court, it could be a persuasive factor for a jury. But knowing that lie detectors are not always reliable could work to your advantage.
Do we really need lie detector tests?
The recent revelations that the CIA used torture as a means of obtaining information from suspected terrorists has made this research particularly pertinent. Others are worried that law enforcement agencies will come to rely too heavily on polygraphs rather than conducting more holistic investigations.

Word Watch

One test involved a lost wallet containing £5. Some subjects were asked to bring the wallet to a lost-and-found box while others hid it and lied. Based on the limb movements, scientists correctly classified 82.2% of the interviewees.
Psychopathy is a personality disorder characterised by antisocial behaviour and difficulty in empathising with other people.
Polygraphs famously failed to trap the double-agent Aldrich Ames, who passed two tests while spying for the USSR. Forcing the body to stay relaxed or biting the tongue to increase pain (and therefore stress levels) are ways of fooling a polygraph test. Some think the new test could be defeated by keeping the body tense throughout the interview.
Some scientists have turned to brain scanners in order to tell if someone is lying. But as there is no centre for dishonesty in the brain, the results have also proved unreliable.
A dystopia is a society characterised by human misery and oppression. It is the opposite of a utopia; an imagined state or place where everything is perfect.

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