How Lie Detectors Work

Source: How Lie Detectors Work

http://people.howstuffworks.com/lie-detector.htm

My Topic: The lie detector is not always accurate.

What I hope to learn from this source:

I want to know the principles of the lie detector. 

Notes:

Polygraphs, commonly called "lie detectors," are instruments that monitor a person's physiological reactions.

A polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring in the body. As a person is questioned about a certain event or incident, the examiner looks to see how the person's heart rate, blood pressure, respiratory rate and electro-dermal activity (sweatiness, in this case of the fingers) change in comparison to normal levels. Fluctuations may indicate that person is being deceptive, but exam results are open to interpretation by the examiner.­

Polygraph exams are most often associated with criminal investigations, but there are other instances in which they are used. You may one day be subject to a polygraph exam before being hired for a job: Many government entities, and some private-sector employers, will require or ask you to undergo a polygraph exam prior to employment.

Polygraph examinations are designed to look for significant involuntary responses going on in a person's body when that person is subjected to stress, such as the stress associated with deception. The exams are not able to specifically detect if a person is lying, according to polygrapher Dr. Bob Lee, former executive director of operations at Axciton Systems, a manufacturer of polygraph instruments. But there are certain physiological responses that most of us undergo when attempting to deceive another person. By asking questions about a particular issue under investigation and examining a subject's­ physiological reactions to those questions, a polygraph examiner can determine if deceptive behavior is being demonstrated.­ ­

>>>>Final Thoughts:

The lie detector called 'polygraph' records person's heart rate, blood pressure, respiratory rate and electro-dermal activity compare to normal levels.  Through these information, It can determine if deceptive behavior is being demonstrated.­