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Typically, a person who is lying or deceiving others will experience guilt and anxiety.

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These emotions produce physiological arousal in the body

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leading to characteristic changes in body posture and movements

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as well as specific gestures or facial expressions.

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Unfortunately, most people are not very good at reading these nonverbal cues

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or using them to detect deception

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The most common method of lie detection involves using a polygraph to record the activity of the sympathetic nervous system

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by measuring heart rate, perspiration, breathing rate, and other physiological responses.

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Polygraph examiners ask “control questions” to establish baseline rates of activity

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then ask “relevant questions” to see if the level of arousal changes.

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If a suspect shows more nervousness while answering relevant questions

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that person would be judged as lying.

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Research suggests that the judgments of polygraph examiners are correct only about two-thirds of the time.

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Examiners make two kinds of errors: misses (judging guilty people as innocent)

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The high false alarm rate is the main reason that polygraph evidence is not admissible in court.