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The Polygraph detects physiological changes in the body due to a psychological stimuli. When humans feel or sense danger, the autonomous nervous system, also called the sympathetic nervous system sets our body in a stage called fight, flight or freeze. This stage is a natural occurance that cannot be controlled by human beings, no matter how me may appear or try. This stage triggers the human body to undergo slight changes that can be measured by polygraph channels. These readings are then confirmed by repeating the same test and observing the results.

A Polygraph Examination takes approximately 1 to3 hours from beginning to end and consists of four different phases:

  1. Pre-Test Interview,
  2. Chart Collection,
  3. Analysis of Charts and
  4. Post-Test Interview

1. Pre-Test Interview

During the Pre-Test Interview, the examiner explains how the polygraph works, discuss the issue in-depth that is under investigation, develop and review all questions that will be asked on the Polygraph Exam. This stage is known to be the longest to complete and is among the most crucial components of the polygraph exam because the examinee must take a position; to lie or be truthful.

The examinee is then attached to the instrument as follows:

Pneumographs measure the respiratory function. Two pneumographs (rubber tubes filled with air) are placed around the test subject's chest and abdomen. When the chest or abdominal muscles expand, the air inside the tubes is displaced. In an analog polygraph, the displaced air acts on a bellows, an accordion-like device that contracts when the tubes expand. This bellows is attached to a mechanical arm, which is connected to an ink-filled pen that makes marks on the scrolling paper when the subject takes a breath. A digital polygraph also uses the pneumographs, but employs transducers to convert the energy of the displaced air into electronic signals.

A blood-pressure cuff is placed around the subject's upper arm. Tubing runs from the cuff to the polygraph. As blood pumps through the arm it makes sound; the changes in pressure caused by the sound displace the air in the tubes, which are connected to a bellows, which moves the pen. Again, in digital polygraphs, these signals are converted into electrical signals by transducers.

Fingerplates called galvanometers (GSR) are attached to two of the subject's fingers. These plates measure the skin's ability to conduct electricity. When the skin is hydrated (as with sweat), it conducts electricity much more easily than when it is dry.

All the information gathered from the pnuemographs, the cuff and the GSR feed into the polygraph, on to a computer screen and finally on to a set of charts for the examiner to render a professional opinion.

2. Collection of Charts

During this phase, the subject will be attached to the polygraph. The question set which was developed during the Pre-Test Interview and reviewed with the examinee will be asked to the examinee 2 to 4 times. There will be between 20 and 45 seconds in between each question in order to get a precise reading of the stimulus.

3. Analysis of Charts

Once the examiner has collected the charts, he/she will carefully analyze the polygrams. The examiner then renders an opinion and those polygrams are additionaly reviewed by another examiner as part of B.E.A.R. FORENSICS Quality Control Program. Only after a stringent evaluation and review process is a final decision rendered.

4. Final report

The findings and results of the polygraph examination is then summarized in a final report that includes the relevant questions asked during the polygraph examination as well as the polygraph examiner’s professional opinion.

The decisions of a polygraph exam are as follows:


  • No Deception Indicated (The examinee was truthful about his responses to the issue under investigation)

  • Deception Indicated (The examinee was not truthful about his responses to the issue under investigation)

  • Inconclusive (Insufficient data was gathered in order to make a professional judgment of the examinee’s)



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