[00:04.66]Modern lie detectors-
[00:05.98]also known as "polygraphs"-
[00:07.67]rely on the same basic principle-
[00:09.88]that lying causes bodily changes,
[00:12.57]which can be detected and measured.
[00:14.72]Having agreed to do the test
[00:16.75](if the test is done under duress,
[00:18.68]the extra stress caused
[00:20.43]makes the test unreliable),
[00:22.52]the suspect is connected to three devices
[00:24.96]measuring blood pressure,
[00:26.70]breathing rate and eletrodermal response
[00:30.27](the increased amount of electricity
[00:31.85]which flows to the skin when we sweat).
[00:34.75]Increased activity in these areas
[00:37.48]suggests increased stress...
[00:39.90]which means the subject might be lying.
[00:42.83]Lie detectors have been widely used
[00:45.04]in the US since the 1950s
[00:47.31]but they remain controversial
[00:49.16]and their results are not
[00:50.56]always accepted by courts.
[00:53.11]The results of a test taken by the British
[00:55.76]nanny Louise Woodward to support her plea
[00:58.59]of not guilty to killing a child
[01:00.94]in her care were not admitted as evidence
[01:04.12]at her trial in Massachusetts.
[01:06.62]Nowadays, polygraphs are used by the US police,
[01:10.05]the CIA and the FBI to screen job applicants,
[01:14.09]but private employers are not allowed
[01:16.26]to subject job candidates
[01:18.20]to polygraph examinations,except in a few high
[01:21.75]-security industries like pharmaceuticals
[01:24.42]and money manufacturing.
[01:24.94]
