Abhi Lie 572830

Presented By : Abhishek Kumar Singh

29-Sep--2009

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Introduction Lie Detector Polygraph Machine Using A Lie Detector Scientific Validity Application Limitation Conclusion

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Lie is a type of deception in form of untruthful statement, especially with intention to deceive others. Lie detection is the practice of determining whether someone is lying. Lie detector is controversial topic that how can a machine tell truth?

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Do not detect lies. Detect deceptive behaviour only. Polygraphs are commonly called Lie Detectors.

Fig: Lie Detection 29-Sep--2009

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Lie detection commonly involves the polygraph. Detects changes in body functions not easily controlled by the conscious mind.

Fig: Polygraph Test

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Can be built in few seconds. Not sophisticated as professionals use. Measures skin resistance ,which goes down on lying.

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Fig: Circuit Diagram 29-Sep--2009

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Circuit works on fact that a person's skin resistance changes when they sweat . Dry skin has R=1 million ohms, moist skin resistance is reduced by a factor of ten or more.

Fig: Circuit Diagram 29-Sep--2009

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Oscilloscope shows the variation of skin resistance versus time. One electrode is taped to the palm of each hand. Variations in skin resistance varies current in the circuit.

Fig: oscilloscope as a Lie Detector 29-Sep--2009

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Used to find the truth or falsity of statements. Answers of control questions and actual questions are compared. When people lie they get measurably nervous about lying.

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Invented by James Mackenzie in 1902. The name is polygraph because it records different responses. Monitors physiological activities: Respiratory rate B.P./ Heart rate GSR

Fig: Polygraph Machine

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Fig: Graph Showing Different Measures 29-Sep--2009 11

Fig : Block diagram 29-Sep--2009

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Validity mean accuracy of the test in detecting deception. Polygraphs are dependent on trickery. Should give equivalent outcomes when subjects are retested. But its not true. Its validity is not scientifically established. So It is not 100% accurate.

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In police departments, and state governments, and numerous private agencies. Can use by truthful persons. Against doping in games. In future, you may go through polygraph exam before being hired for job. T.V. shows are using it.

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Habitual liar can easily this test. The test depends on trickery, not on science. It is completely without any theoretical foundation. However, Used in police interrogation and investigation since 1924, the lie detector is still controversial among psychologists, and is not always judicially acceptable.

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Has become a cultural icon. Being used from many years. But has various applications. The test depends on trickery, not science. So it is not 100% judicable.

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