Can you fool a lie detector? © Getty Images

Can you fool a lie detector?

Liar, liar, pants on fire! There are a few ways to trick a polygraph test.

Asked by: Lizzie Dawes, Braunton

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The polygraph test, still used widely in the US, measures your heart rate, breathing and blood pressure as a way to tell how stressed you are feeling. The idea is that the interrogator asks you questions and when you lie, you get more stressed than when you tell the truth, and this difference is revealed in the physiological measures.

A simple way to cheat the polygraph is to deliberately distort your physiological readings when telling the truth, such as by biting your tongue, or imagining an embarrassing incident in the past. Similar problems afflict brain scan lie detectors, which follow the same principle of needing a reliable baseline against which to compare signs of lying.


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