Polygraph Machine – How Does a Lie Detector Work?
Humans are taught to believe that lying is morally and biblically wrong. Whenever they are under pressure, they lie intentionally or unintentionally. Lying produces nervousness and anxiety. These two conditions in turn produce distinct physiological effects that are sometimes visible and most often measurable in a lie detection machine such as a polygraph. The physiological effects of lying include:
- An increase in breathing rate accompanied by a decrease in the depth of each breath, also known as shallow breathing. These effects are measured by the pneumograph aspect of the lie detector.
- An increase in blood pressure and pulse rate. These vital signs are measured by the cardiograph aspect.
- An increase in sweating. The galvanograph aspect measures the difference in the electrical resistance of the skin as the subject sweats under pressure. The electrolyte concentration found in sweat promotes perspiration which in turn increases electrical conductivity. It does not measure the amount of sweat directly.
The lie detector machine records the measurements on an analog graph. Over the last half century or so, analog polygraphs have traced out their measurements on moving paper rolls which look similar to fax paper rolls on early 90’s fax machines. These papers are then annotated by the examiner during the polygraph test and read after the completion of the test.
More recently, polygraph machines have been hooked up to and its measurements recorded onto laptop or desktop computers thus making it easier for the examiner to administer the test without having to fumble around with lengthy paper rolls. Computers have revolutionized the way polygraphs are recorded. Computers have made analog polygraphs obsolete and make it efficient in storing the results of multiple subjects in one place.
The most important aspect of digital polygraph machines is the software program. The software program includes chart analysis capabilities designed to help the examiner in interpreting the results.
Again, the results of digital polygraph tests can be inconclusive provided that the test subject has had previous surgeries, illnesses, or is taking drugs, medications, or alcohol.
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