Polygraph

A polygraph, commonly referred to as a lie detector, is a device and procedure that records several physiological signals to assess whether a person is being deceptive during questioning. It traditionally measures respiratory effort, cardiovascular activity (such as heart rate and blood pressure), and skin conductance, and may also monitor muscle activity. The underlying premise is that deceptive responses provoke physiological arousal that these measurements can reflect.

During a polygraph examination, a trained examiner conducts a pre-test to establish baseline responses and then presents a series of questions, including relevant questions related to the issue, control questions designed to elicit responses from someone who is lying in general, and sometimes additional questions about known facts. The examiner interprets the recorded data, noting fluctuations associated with different questions. Modern practice may use computerized scoring, but there is no universally accepted interpretation standard, and outcomes are typically described as indicators of likelihood rather than definitive proof of deception.

Validity and legal status of polygraph testing are subjects of ongoing debate. Critics highlight issues such as false positives, false negatives, and vulnerability to countermeasures, leading many courts to restrict admissibility of polygraph results. Some jurisdictions permit polygraph use in certain contexts, such as criminal investigations, personnel security screenings, or internal inquiries, but not as standalone evidence. Proponents argue that the test can aid investigations when used as part of a broader evidentiary process.

History and development: The modern polygraph evolved in the early 20th century with contributions from researchers including John Larson and Leonard Keeler, advancing from rudimentary physiological measurements to contemporary multi-parameter instruments.