What is a Lie Detector Test?


Lie detection, or a polygraph test as it often called, utilises both technology and questioning techniques to analyse physiological functions in an attempt to conclude whether a person is telling the truth. Despite the fact it has been described as an ‘inexact science’ it is widely used in America by the police and security services, who appear to have far great confidence in the testing procedure than other law enforcement authorities around the world.

Whenever the phrase ‘lie detector test’ is mentioned in conversation the first thing people will often think of is the lie detector machine or polygraph as it is often referred to as. This is not surprising as polygraph usage is prevalent in most lie detection scenarios and is often seen in television and film. The big question surrounding them however, is ‘Do they actually work?’. Before we examine this pertinent question it would be wise to discuss the history and evolution of lie detection over the course of the last two centuries.

The use of physiological methods for the purposes of lie detection started in the early 1900s. Vittorio Benussi was one of the early proponents of such methods and began looking into the physiological changes that may indicate deception. His first finding was that changes in the ratio of inspiration to expiration may provide an insight as to whether someone was telling the truth, a theory later confirmed Burtt. Changes in blood pressure were studied by both Burtt and Marston and perceived to be an accurate method of determining if a person was being deceptive or not, however critics of this method pointed out that blood pressure is easily changeable and would require constant measuring to provide accurate data.

lie detector test

In the 21st Century DePaulo and Morris identified a correlation between not telling the truth and pupil size. They also stated that liars will also appear more nervous than their truth-telling counterparts, and whilst they may not exhibit such traits as more rapid blinking, increased fidgeting and body posture tension, liars do tend to press their lips together more so than those not telling untruths. Upon examining the verbal and written outputs of liars (in an attempt to find conclusive patterns) they found that those not telling the truth take longer to start answering questions unless they have time to plan. If they do have time to plan they then will answer questions far quicker than those telling the truth. Other traits they ascertained were more prevalent in liars were negativity, being more likely to complain and being less cooperative.

A method known as LWIC (Linguistic Inquiry and Word Count) was used by James Pennebaker to analyse written content of supposed liars. Pennebaker claimed that the method was more effective than human judges who has been trained to spot lies. After several experiments conducted this was proven to be true with LWIC identifying 67% of those not telling the truth compared to 52% for the judges. He concluded that liars refrain from using statements of ownership, distance themselves from their stories and generally tend to avoid taking responsibility. In recent years the CA Morgan has ventured into the field of computer technology as a means to analyse speech that would usually be assessed solely by a human lie detection professional. Not only does this method have sound scientific grounding, it also doesn’t require any form of ‘interview’ or one on one situation, which can cause a stress response in those being questioned.

As you can see the evolution of lie detection has progressed through many methods of the course of the last few hundreds years and what we have arrived at today is a technology coupled with professional human judgement. This combination is widely regarded as the best and most comprehensive method when it comes to lie detection.

For more information on lie detector tests please go to: http://www.liedetectortest.ie