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