How exactly does a lie detector tell if you're lying?

Brainyblonde

A polygraph (commonly and inaccurately referred to as a "lie detector") is a device which measures and records several physiological variables such as blood pressure, heart rate, respiration and skin conductivity while a series of questions are being asked, in an attempt to detect lies. The above measurements are posited to be indicators of anxiety that accompanies the telling of lies. Thus, measured anxiety is equated with telling untruths. However, if the subject exhibits anxiety for other reasons, a measured response can result in unreliable conclusions. http://en.wikipedia.org/wiki/Polygraph Aug 21 06, 3:32 PM

zbeckabee

When a person takes a polygraph test, four to six sensors are attached to him. A polygraph is a machine in which the multiple ("poly") signals from the sensors are recorded on a single strip of moving paper ("graph"). The sensors usually record: The person's breathing rate The person's pulse The person's blood pressure The person's perspiration Sometimes a polygraph 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 being tested by the polygraph are asked. Throughout questioning, all of the person's signals are recorded on the moving paper. http://science.howstuffworks.com/question123.htm Aug 21 06, 4:45 PM

Allergic2Life

Polygraph results are not admisible in most state's courts as evidence because they are so unreliable. The drug sodium pentathol is also used to expose the truth, but that is just as unreliable. Aug 21 06, 4:59 PM

What-A-Mess

The single most important detector during a polygraph is the interviewer. The method and delivery of the questions is the key to response manipulation. The prescreen, the test and the post interview questions will tell a lot. A typical polygraph starts with a pre-test interview designed to establish a connection (or find a scientific control) between the tester and the testee and to gain some preliminary information which will later be used for "Control Questions " or C (see below). Then the tester will explain the polygraph, emphasizing that it can detect lies and that it is important to answer truthfully. Then a "stim test" is often conducted: the testee is asked to deliberately lie and then the tester reports that he was able to detect this lie. Then the actual test starts. Some of the questions asked are "Irrelevant " or IR ("Are you 35 years old?"), others are "probable-lie" Control Questions that most people will lie about ("Have you ever stolen money?") and the remainder are the "Relevant Questions " or R the polygrapher is really interested in. The different types of questions alternate. The test is passed if the physiological responses during the probable-lie control questions are larger than those during the relevant questions. If this is not the case, the tester attempts to elicit admissions during a post-test interview ("Your situation will only get worse if we don't clear this up"). WIKI Aug 21 06, 6:36 PM

Baloo55th

I've always wondered about the point of testing on an asked-for deliberate lie. The person testing won't be nearly as stressed telling a test lie as he/she would be telling a real one under proper conditions. And anyone being subjected to a lie-detector test will be stressed anyway no matter what they're telling. Aug 22 06, 10:31 AM

ItalianBabe2

That's what I thought. Thank you! Aug 25 06, 5:56 PM