The Lie Detector and Polygraph

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A Polygraph test is commonly known as Lie Detector. Scientists have developed methodology to identify cheating, fraud, trickery and finding truth, which is Lie detection or polygraph testing. Polygraph tool evaluates several physiological procedures and the reactions that one goes through in those processes. Mainly Lie Detector testing is used for crime detection and Employee screening.

Brief History of Lie Detector

In the year 1902 inadequate lie detector test was invented by James McKenzie.  In 1921 John Larson invented modern polygraph instrument which gives recorded information on a smoke paper.  In 1925 Leonard Keeler further developed instrument with ink pens instead of smoke paper to get better results.  Finally in 1992 machine was computerized to record results accurately.

Lie Detection with Polygraph Testing

Lie detection took on scientific aspects with the development of techniques that use measures of physiological responses as indicators of deception. The physiological measurements include heart rate, blood pressure, body movements and electrical conductance in skin. The polygraph instrument contains sensors to measure the physiological phenomena. In polygraph instrument depth of respiration and heart rate are measured by pneumographs chest wrapped, skin conductivity is measured through electrodes attached to finger tips and a blood pressure BP cuff attached on upper arm. While conducting examinations sensors transmit the data to the instrument and print that data on Polygraph Chart.

Lie Detector Testing Techniques

The examiner who conducts the test interprets the deception depending on the Polygraph Chart. The Interpretation involves comparison of physiological responses with relevant questions.  In the preliminary phase the examiner conducts pre-test to get primary information from the examinee for further investigation. Three major questioning techniques are in current use.

  1. Relevant-Irrelevant Technique: The relevant questions are very specific and related to the issue, where the irrelevant questions are completely not related to the issue. The stronger physiological responses for the relevant and irrelevant questions taken as indicative of deception. This technique is widely used in Criminal case investigations and employee screening.
  2. Control Question Technique: It is also called as comparison question technique. It uses control questions with known answers to create physiological responses in order to compare them with relative questions. Controlled questions are designed to concern about the past truthfulness.  The stronger response to control questions leads to judgment of non-deception.  If there is no difference between control and relative questions there will be ambiguity in decision making.
  3. Guilty Knowledge Polygraph Testing: This test consists of multiple choice questions. The examiner asks random questions of their knowledge based on the case. If the examinee responds strongly to guilty information, the greater physiological response should be to correct answer.