WEBVTT - How Polygraph Machines Work

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<v Speaker 1>Welcome to brain Stuff from how stuff works dot com

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<v Speaker 1>where smart Happens. Hi, I'm Marshall Brain with today's question

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<v Speaker 1>how does a polygraph machine work? You hear about lie

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<v Speaker 1>detectors all the time and police investigations, and sometimes a

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<v Speaker 1>person applying for a job will have to undergo a

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<v Speaker 1>polygraph test. The goal of a lie detector is to

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<v Speaker 1>see if the person is telling the truth or lying

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<v Speaker 1>when answering certain questions. Four to six sensors are attached

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<v Speaker 1>to a person taking a polygraph test. A polygraph was

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<v Speaker 1>originally a machine in which multiple or polly signals from

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<v Speaker 1>these sensors were recorded on a single strip of paper.

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<v Speaker 1>That's the graph part you get polygraph. Today, most of

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<v Speaker 1>the recording is done on a laptop instead of a

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<v Speaker 1>piece of paper. The sensors usually record the person's breathing rate,

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<v Speaker 1>the person's pulse, the person's blood pressure, and the person's

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<v Speaker 1>perspiration level. Sometimes a poly graph will also record things

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<v Speaker 1>like arm and leg movement. When the polygraph test starts,

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<v Speaker 1>the questioner asks three or four simple questions to establish

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<v Speaker 1>the norms for the person's signals. Then the real questions

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<v Speaker 1>begin throughout questioning all of the person's signals are recorded

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<v Speaker 1>both during and after the test. A polygraph examiner can

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<v Speaker 1>look at the graphs and can see whether the vital

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<v Speaker 1>sides change significantly on any of the questions. In general,

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<v Speaker 1>a significant change such as a faster heart rate, a

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<v Speaker 1>higher blood pressure, increased perspiration means that the person is lying. However,

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<v Speaker 1>because the examiner's interpretation is subjective and because different people

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<v Speaker 1>react differently to lying, a polygraph test is not perfect

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<v Speaker 1>and it can be fooled. Do you have any ideas

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<v Speaker 1>or suggestions for this podcast? If so, please send me

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<v Speaker 1>an email at podcast at how stuff works dot com.

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<v Speaker 1>For more on this and thousands of other topics, go

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<v Speaker 1>to houstaff works dot com. M