Speaker 1: Welcome to brain Stuff from how stuff works dot com
Speaker 1: where smart Happens. Hi, I'm Marshall Brain with today's question
Speaker 1: how does a polygraph machine work? You hear about lie
Speaker 1: detectors all the time and police investigations, and sometimes a
Speaker 1: person applying for a job will have to undergo a
Speaker 1: polygraph test. The goal of a lie detector is to
Speaker 1: see if the person is telling the truth or lying
Speaker 1: when answering certain questions. Four to six sensors are attached
Speaker 1: to a person taking a polygraph test. A polygraph was
Speaker 1: originally a machine in which multiple or polly signals from
Speaker 1: these sensors were recorded on a single strip of paper.
Speaker 1: That's the graph part you get polygraph. Today, most of
Speaker 1: the recording is done on a laptop instead of a
Speaker 1: piece of paper. The sensors usually record the person's breathing rate,
Speaker 1: the person's pulse, the person's blood pressure, and the person's
Speaker 1: perspiration level. Sometimes a poly graph will also record things
Speaker 1: like arm and leg movement. When the polygraph test starts,
Speaker 1: the questioner asks three or four simple questions to establish
Speaker 1: the norms for the person's signals. Then the real questions
Speaker 1: begin throughout questioning all of the person's signals are recorded
Speaker 1: both during and after the test. A polygraph examiner can
Speaker 1: look at the graphs and can see whether the vital
Speaker 1: sides change significantly on any of the questions. In general,
Speaker 1: a significant change such as a faster heart rate, a
Speaker 1: higher blood pressure, increased perspiration means that the person is lying. However,
Speaker 1: because the examiner's interpretation is subjective and because different people
Speaker 1: react differently to lying, a polygraph test is not perfect
Speaker 1: and it can be fooled. Do you have any ideas
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