How does a lie detector work?

Answer 1

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.

A polygraph test is also known as a psychophysiological detection of deception (PDD) examination. The original polygraph was invented by John A. Larson.

Today, polygraph examiners use two types of instrumentation, analog and computerized. In the United States, most examiners now used computerized instrumentation.

Answer 2

It detects your blood pressure, heart rate, if you are lying then you should be a little tensed and the lie detector will detect you but lie detectors are'nt always good, there is only a 50:50 chance that you'll be caught as you can suppress the lie detector by not being tensed!

Answer 3

Some models monitor breathing rate and pulse; others check the conductivity of your skin (when you lie, you involuntarily start to sweat, which makes you conduct electricity better). Some can even detect the loss of tremors in your voice when you lie -- someone monitoring a phone conversation could conceivably have you "hooked up" to a lie detector!

Answer 4

The device is monitoring blood stress, respiration and different body applications. The premises is that the body is going by quite some adjustments even as mendacity to someone. The device possibilities up this flunctuation. the reason lie detector assessments at the on the spot are not utilized in reference suggested on your question, quite some legal causes: the detector isn't sturdy, some human beings recognize a thanks to "trick" the device, and others that i'm positive are obtainable yet i do not recognize them. someone with a touch extra legalese than me might want to be in a position to percentage another causes.

Answer 5

A lie detector is hooked up to you so that it can detect when there is any change in your rate of perspiration and pulse. General questions, such as your name and date of birth, are asked first to determine what your pulse is when you answer questions truthfully, and then they are able to determine whether other answers are truthful as well.

Answer 6

It senses your heart rate and monitors your sweat glands. There are some unconscious things that a person does when they lie that they cannot cover up. You can have false readings and that is why many states do not accept polygraphs in court.

Answer 7

to detect if your heart beat or emotions change when you answer or hear a question, YES

Answer 8

it works by measuring your neural response...your brainwaves tell them when you are agitated, You sweat glands help...you sweat more when you lie.
Inteteresting stuff...

Answer 9

I detects wheter or not that you are lying.

Answer 10

Polygraph results are sometimes recorded on a chart recorderA 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.

A polygraph test is also known as a psychophysiological detection of deception (PDD) examination. The original polygraph was invented by John A. Larson.

Today, polygraph examiners use two types of instrumentation, analog and computerized. In the United States, most examiners now used computerized instrumentation.

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").

While some people believe that polygraph tests are reliable, there is little scientific evidence to buttress this claim. For example, while some claim the test to be accurate in 70% - 90% of the cases, critics charge that rather than a "test", the method amounts to an inherently unstandardizable interrogation technique whose accuracy cannot be established. Critics also argue that even given high estimates of the polygraph's accuracy a significant number of subjects (e.g. 10% given a 90% accuracy) will appear to be lying, and would unfairly suffer the consequences of "failing" the polygraph. It is interesting to note that, so far, no scientific study has been published that offer convincing evidence of the validity of the polygraph test. Polygraph tests have also been criticized for failing to trap known spies such as Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union.

Several countermeasures designed to pass polygraph tests have been described, the most important of which is never to make any damaging admissions. Additionally, several techniques can be used to increase the physiological response during control questions. In an interview, Ames was asked how he passed the polygraph test. His response was that when told he was to be polygraphed he asked his Soviet handlers what to do, and was quite surprised that their advice was simply to relax when being asked questions, which he did.

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2003 National Academy of Sciences Report
The accuracy of the polygraph has been contested almost since the introduction of the device. In 2003, the National Academy of Sciences (NAS) issued a report entitled “The Polygraph: Truth and Lie Detection”. The NAS found that the majority of polygraph research was of low quality. After culling through the numerous studies of the accuracy of polygraph detection the NAS identified 57 that had “sufficient scientific rigor”. These studies concluded that a polygraph test regarding a specific incident can discern the truth at “a level greater than chance, yet short of perfection”. The report also concluded that this level of accuracy was probably overstated and the levels of accuracy shown in these studies "are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field.” [1]

When polygraphs are used as a screening tool (in national security matters and for law enforcement agencies for example) the level of accuracy drops to such a level that “Its accuracy in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee security screening in federal agencies.” In fact, the NAS extrapolated that 10,000 polygraph tests searching for spies would incorrectly classify 99.5% of “deceptive” results (those telling the truth yet incorrectly deemed to be deceitful), and incorrectly classify 20% of deceitful subjects. The NAS did conclude that the polygraph “…may have some utility” [2] and that there is "little basis for the expectation that a polygraph test could have extremely high accuracy."[3]

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Admissibility of polygraphs in Court
While polygraph tests are commonly used in police investigations in the US, no defendant or witness can be forced to undergo the test. In United States v. Scheffer (1998) [4], the US Supreme Court left it up to individual jurisdictions whether polygraph results could be admitted as evidence in court cases. Nevertheless, it is used extensively by prosecutors, defense attorneys, and law enforcement agencies who believe in its utility.

In the United States, the State of New Mexico admits polygraph testing in front of juries under certain circumstances. In many other states, polygraph examiners are permitted to testify in front of judges in various types of hearings (Motion to Revoke Probation, Motion to Adjudicate Guilt).

In most European jurisdictions, polygraphs are not considered reliable evidence and are not generally used by police forces. However, in any lawsuit, an involved party can order a psychologist to write an opinion based on polygraph results to substantiate the credibility of its claims. The party must bear the expense themselves, and the court weighs the opinion like any other opinion the party has ordered. Courts themselves do not order or pay for polygraph tests. An example of this practice would be a rape trial in which the defendant tries to fortify his testimony by submitting himself to a polygraph session.

In Canada, the use of a polygraph is sometimes employed in screening employees for government organizations. However, in the 1987 decision of R. v. Béland, the Supreme Court of Canada rejected the use of polygraph results as evidence in court.

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Use with Sex Offenders
Sexual Offenders are now routinely polygraphed in many states and it is often a mandatory condition of probation or parole. In Texas, a state appellate court has upheld the testing of sex offenders under community supervision and has also upheld written statements given by sex offenders if they have re-offended with new victims. These statements are then used when a motion is filed to revoke probation and the probationer may then be sentenced to prison for having violated his or her probation.

A significant number of Federal appeals courts have upheld polygraph testing for Federal probationers as well. The most recent decision was by the Second Circuit Court of Appeals regarding a New York sex offender.

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History
Similar techniques were used in the ancient times. For instance, in West Africa persons suspected of a crime were made to pass a bird's egg to one another. If a person broke the egg, then he or she was considered guilty. In Ancient China, during a prosecutor's speech the suspect held a handful of rice in his or her mouth. Since salivation was believed to cease at times of emotional anxiety, the person was considered guilty if by the end of that speech the rice remained dry