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What is a polygraph test?
A polygraph, commonly known as lie detector, is a device used to detect lies by measuring several physiological variables of the person being questioned. While taking a polygraph test, a person gets four to six sensors attached to hisher body. The polygraph machine records multiple (hence “poly“) signals from the sensors on a single strip of moving paper (“graph“). The sensors usually record the person’s blood pressure, heart rate, respiration and perspiration rate while he is asked a series of questions. The main principle behind this test is based on the ancient hypothesis of nervousness while telling a lie.
How effective is the test?
The accuracy of the polygraph has been contested almost since the introduction of the device. Nearly eight decades after their invention, polygraph tests are not admissible in court. In some countries, lie detectors are used for background checks during job interviews and during police investigations to extract more information from the suspect, but the results are not admissible in courts. Various studies suggest that the results could get distorted if the subject exhibits anxiety for reasons other than guilt. They can also be wrong if the person can control his or her anxiety level.In other words, a measured response can result in unreliable conclusions.
What are the other methods of determining the truthfulness and accuracy of an accused person’s statements?
Apart from polygraph tests, investigators also use narco-analysis, which is the use of a truth serum and brain mapping to ascertain the reliability of the ac cused person’s statements.
Like the results of poly graph tests, the results of narco-analysis as well as the accused persons’ state ments under the influence of these drugs are not ad missible evidence in courts. They are primarily used only during the investigation. Results of brainmapping or brain fingerprinting has been used in a handful of cases in the US as a proof of guilt or innocence.
What is narco-analysis?
The Latin expression “in vino veritas“ meaning `’truth in wine” shows that alcohol can be the one of the oldest truth sera. The term narco-analysis is derived from the Greek word narke meaning “numbness “ and is used as a psychotherapeutic as well as an interrogating technique that uses barbiturate drugs or truth se rums to induce a state of unconsciousness in which secrets come to the surface, where they can be exploited by the therapist. In modern times, sodium thiopental or sodium pentothal is widely used as a truth serum. This drug decreases higher cortical brain functioning. The main principle which works in this analysis is the hypothesis that lying is more complex than truth and hence a lower level of cortical activity will force the subject to tell the truth.
What is brain-mapping, and how does it work?
American scientist Lawrence Farwell is credited with developing brain mapping or brain fingerprinting technology. This system determines whether or not specific information is stored in a person’s memory . The test measures individual brain-wave responses to relevant words, pictures or sounds presented by a computer. Our brain has the capacity to store events as memories.This function of the brain is used in differentiating a criminal and an innocent person. The criminal’s brain stores the sequence of events that happens at the crime scene, an innocent man’s brain however would have no such memories. The brain fingerprinting method scientifically detects the presence or absence of specific information. Words, pictures, codes and sounds related to the crime are presented to the subject by a computer.