Polygraph Machine
Lie detectors are also known as polygraphs. A polygraph test consists of simultaneously monitoring several of an individual's physiological functions, breathing, pulse, and galvanic skin response. While being monitored, a graph is generated, traditionally on paper. The graph, consisting of plotted lines for each monitored function, shows exactly when, during the questioning period, the biologic responses occurred. If the period of greatest biologic reaction lines up with the key questions on the graph paper, it is considered an indication of stress related to deception. Rarely can a person control all three physiological functions at the same time to successfully deceive without detection. When a failure to detect deception occurs, it is typically due to an inexperienced or incompetent polygraph machine operator or the use of medication such as a sedative.
The standard lie detector monitors 3 physiological processes.
- pulse (heart rate)
- respiration (breathing)
- blood pressure
Some polygraph machines monitor additional processes.
- galvanic skin response (electrical conductivity of the skin)
- perspiration (sweating)
A modern polygraph can monitor several involuntary physiological activities, including blood pressure, skin resistivity, pulse rate, respiration, and sweating. Some polygraph machines are designed to be portable, while others are large medical devices. The individual trained to administer the lie detector test is known as the polygrapher.
There are three basic approaches to the polygraph test:
- Control Question Test (CQT)
- Directed Lie Test (DLT)
- Guilty Knowledge Test (GKT)
Polygraphs measure physiological arousal which can pinpoint deception rather than "lies". In 2003, the National Academy of Sciences found that the majority of polygraph research was "unreliable, unscientific and biased." Studies showed that specific-incident polygraph testing, in a person untrained in counter-measures, could discern the truth at "a level greater than chance, yet short of perfection."
"I don't know anything about lie detectors other than they scare the hell out of people." --Richard Nixon
Contents
Objective Scoring System, version 3 (OSS-3)
A computerized polygraph scoring model designed to increase the accuracy of Polygraph results where operator interpretation can introduce variables. OSS-3 uses far fewer criteria for evaluating data than other systems but it requires scrupulous attention to the scoring protocol to deliver these advantages over traditional 7-position scoring. OSS-3 is a way to replace reliance on the objectivity and skill of the polygrapher.
The name refers to specific commercial software being marketed to aid in lie detection. Most of the information available on OSS-3 comes from the seller of the product.
Polygraph Alternatives
MRI
In recent history it has been discovered that the medical MRI machine can serve as a lie detector. MRI Lie Detectors focus on imaging live the pre-frontal cortex of the human brain. Decision making occurs in the front region of the human mind, and the decision to lie is thereby detectable via the MRI imaging. Using an MRI (Magnetic Resonance Imaging) machine as a lie detector instead of a polygraph is not yet an accepted practice. However, research shows very promising results in more reliable lie detection with this technology.
PCASS
A hand-held lie detector is being deployed by the U.S. Department of Defense is called the Preliminary Credibility Assessment Screening System, or PCASS. The PCASS has been determined to be less reliable than a traditional Polygraph.
vintage machine examples
KEELER model 6303 polygraph machine
The Keeler Model #6303 was a hybrid between the Keller Model #302 and the Model #6308, the first of the PaceSetter Series of polygraphs manufacturered by Associated Reasearch. It was a sleeker design than the Model #302, but still used vacumn tubes. Associated research replaced the stainless steel face with a blue acrylic faceplate.
It had three seperate channels. Pnuemograph, cardiograph, and galvanometer.
polygraph, polygraph machine, psychogalvanic skin response, psychogalvanometer
