Polygraph Machine: How Does a Lie Detector Perform?

Human beings are conditioned to believe that lying is morally and biblically crime. They do not like to lie but do so consciously or unconsciously while they are under pressure. Lying produces uneasiness and anxiety. These two conditions in turn generate different physiological effects that are occasionally visible and most often detectable in a lie detection device such as a polygraph. The physiological effects of lying include:

• An rise in breathing rate accompanied by a decrease in the depth of each breath, also well-known as shallow breathing. The pneumograph aspect of the polygraph measures these effects.
• An rise in blood pressure and pulse rate. The cardiograph aspect measures these essential signs.
• An rise in sweating. The galvanograph aspect measures the difference in the electrical resistance of the skin as the question sweats under pressure. Electrical conductivity increases with an rise in sweating due to the electrolyte concentration found in perspiration. It does not compute the amount of sweat promptly.

The lie detector device 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 documents are then annotated by the examiner throughout the polygraph test and read after the completion of the test.

More recently, polygraph technology have been hooked up to and its measurements recorded on laptop or desktop computers hence making it easier for the examiner to administer the test without having to fumble around with lengthy paper rolls. Computers have modernized the method 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 feature of digital polygraph machines is the software code. The software code includes chart analysis capabilities designed to assist the examiner in interpreting the results.

Again, the results of digital polygraph tests can remain unsatisfying provided that the test subject has had earlier surgeries, illnesses, or else is taking drugs, medications, or alcohol.