A lie detector, also called a polygraph, is a device that measures and records several physiological indicators such as blood pressure, heart rate, respiration, and skin conductivity while a person is being asked a series of questions. The assumption is that certain physiological responses are associated with lying or deception, and the polygraph can detect these changes.
The physiological responses measured by a polygraph are:
1. Blood pressure: Blood pressure increases when a person is under stress, which can be caused by lying or being nervous about the test.
2. Heart rate: Heart rate also increases when a person is under stress.
3. Respiration: Breathing patterns can change when a person is lying, such as becoming shallow or irregular.
4. Skin conductivity: Skin conductivity measures the electrical conductance of the skin, which is affected by sweat production. Increased sweating can indicate stress or anxiety.
During a polygraph examination, the individual is asked a series of questions, some of which are known as control questions and some of which are relevant to the matter being investigated. The control questions are designed to elicit a strong emotional response, such as guilt or fear of being caught in a lie, while the relevant questions are designed to elicit a response specifically related to the issue at hand. The examiner compares the physiological responses to the control and relevant questions to identify potential deception.
It's important to note that polygraphs are not foolproof and their accuracy has been debated. While they can provide some information, they are not always reliable in determining whether someone is lying or telling the truth. Other factors, such as psychological countermeasures, nervousness, and physical conditions, can influence the results of a polygraph examination.
Polygraph examinations are sometimes used in criminal investigations, pre-employment screenings, and other security-related contexts, but their use has been controversial due to concerns about their reliability and potential for false positives or false negatives. In many jurisdictions, polygraph results are not admissible as evidence in court.
