Polygraph machines work through three different methods. First, a blood pressure cuff is wrapped around the arm of the person being tested. This measures changes in pulse rate and blood pressure during questioning. Next, metal plates are attached to two of the subject's fingers. These will measure reactions through the skin, such as perspiration. Finally, two tubes made of convoluted rubber are wrapped around the subject's chest and stomach. Convoluted rubber is flexible and will stretch around the body of any subject. It also conducts electricity well. These tubes will monitor respiratory patterns during questioning. All nervous system reactions are sent to a computer and saved.
Lie-detection tools measure the body's involuntary reactions as a person answers questions. Since these reactions must be translated, the information gathered is subjective. Polygraphs--machines used for measuring bodily responses--do not announce whether someone is lying or telling the truth. The results are open to human interpretation, rendering them ineffective in court cases. New tools in lie-detection technology have been developed as of December 2010 and others are in progress.
Voice Stress Analysis
Another tool used in lie detection is a Voice Stress Analysis (VSA) machine. This machine came into use in the 1970s. According to the Polygraph Secrets website, enough police departments have purchased these devices to make them the second most used lie detection tools, behind polygraphs. The appeal of the VSA is it lacks components that attach to the subject and works with live speech or on a voice recording. The voice sample is played on a computer, where certain software is used to detect the body's vocal changes under stress.
Analysis of a subject's facial expressions and reactions during questioning is a form of lie detection that has been researched for years. Researchers believe facial reactions called micro-expressions occur and these reactions convey the true emotional response the subject is trying to hide. These micro-expression often occur within a split second, as a flash of surprise or fear in the eyes or an unintentional tightening of the lips or mouth. Facial and body language experts analyze video of the subject frame by frame. According to the Polygraph Secrets site researchers are working to automate this analysis, which would greatly speed up the process.
Brain Imaging is a lie detection tool that measures the amount of blood sent to different areas of the brain during questioning. The process is called Functional Magnetic Resonance Imaging (FMRI). The device uses a magnet that works with software to track these patterns of blood usage in the brain. The theory behind this process is that more blood appears in a specific area of the brain when that area is in use and that different areas are used when someone lies than when they tell the truth. Practical uses of FMRI, however, have yet to be demonstrated.
- American Polygraph Association: Frequently Asked Questions/What Is a Polygraph
- Polygraph Secrets: Voice Stress Analysis
- Polygraph Secrets: Facial Analysis
- Polygraph Secrets: Brain Imaging
- New Age Industries: Convoluted PTFE Tubing
- Science Daily: Lying Is Exposed By Micro-Expressions We Can't Control
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