Ever wondered how a lie detector detects lies? No, they are not miracle machines that can point out whether you are lying or not just because you say yes or no. Polygraphs are instruments, now for the most part digital instruments that detect several physiological readings of the body to determine your response. This response is then analyzed by experts to give a final verdict.
Earlier analog polygraphs that used needles and paper scripts were used. With the advancement of technology, things have changed drastically and today polygraphs have become completely digital with a higher accuracy rate.
How it works
During polygraph exam wires and tubes are connected to the body in specific locations to track several readings that can reveal deceptive behavior. These readings are discussed below.
1- Respiratory rate
This is recorded using two pneumographs and air-filled rubber tubes attached to the abdomen and chest of the subject. The displacement of the air within the tubes is recorded to know the breath span of the individual.
2- Blood Pressure
This is recorded using a handcuff placed around the upper arm like regular B.P readers. This gives the blood pressure and heart rate readings to the computer for analysis as each question is asked. Critics claim that lie detector are nothing but a scam and may not be as accurate as claimed. However, they can be effective to resolve simple matters that would otherwise require law intervention.
3- Galvanic skin resistance (GSR)
Electro-dermal activity measures the sweat on the fingertips. As people tend to sweat more during stress, finger plates, called galvanometers, are attached to two fingers. They measure the skin’s ability to conduct electricity.
Certain polygraphs are also designed to record body movements as the examinee is being questioned. This is then recorded as well.
Finally, the combination of the result of these recordings is made. This result is then analyzed by an expert who is able to tell through the readings whether a person has spoken the truth or has been deceptive.