polygraphs

A polygraph, commonly known as a lie detector, is a device that records several physiological signals while a person answers questions. The underlying premise is that deceptive responses are associated with measurable arousal, although arousal can stem from anxiety, fear, medical conditions, or other non-deceptive factors.

During a polygraph examination, sensors monitor respiration (chest and abdomen), heart rate and blood pressure, skin conductance, and sometimes muscle activity. The examiner presents a mix of relevant questions related to the issue, along with control or comparison questions designed to provoke a baseline level of arousal. The goal is to identify patterns of physiological response that may indicate deception, as interpreted by the examiner.

Interpretation is complex and controversial. The polygraph does not measure truth directly; it assesses physiological responses that may correlate with deception in some individuals under specific conditions. Results depend on the method used (for example, comparison or control-question tests) and on examiner judgment. Critics point to false positives and false negatives, individual differences in response to stress, and the potential for countermeasures to skew results. In many jurisdictions, polygraph results are not admissible as evidence, or are admissible only under narrow circumstances.

History and use: the modern lie detector originated in the early 20th century with researchers and law enforcement figures who developed techniques to assess truthfulness. Polygraphs have been employed by law enforcement, government agencies, and some employment or security screenings, though regulatory status, standards, and acceptance vary by country and context. Modern practice emphasizes methodological safeguards and trained examiners, but debates about reliability and legal admissibility continue.