Although the
Polygraph is referred to as "A Lie Detector", the polygraph is not a
lie detector in the sense of the word. A lie is spoken....it is a
verbal communication of that which is not the truth. The polygraph
does not monitor or record the voice. In a sense however the answer
to a question is associated with responses that are monitored and
recorded by the polygraph instrument. But no actual lie is recorded
to determine truth or deception. There is in fact no instrument or
device that can actually identify a lie or truth in the spoken word
itself. (see voice stress analysis).
The Polygraph is
derived from two Greek words: Poly - meaning "Many" & Graph -
meaning "writings". This refers to the more than one involuntary
physiological parameter that the instrument monitors and records.
To begin to
understand what the polygraph does, one has to understand a bit
about physiology. We have a built in emergency system. This system
is completely involuntary and is controlled by the autonomous
nervous system. The autonomous nervous system is what causes the
changes to take place in our bodies when we feel threatened and
identify danger. We are all accustomed to these changes and have
experience them at one or other time in our lives.
The next step is
understanding why a person who has committed a crime or dishonest
deed will lie when confronted about it. A person lies because there
are consequences associated with being exposed. A person knows what
they have done and understands that there are consequences in the
event that they are exposed. It is a natural human behavioral
pattern to try and protect ones self and to avoid the consequences.
The best way to do this when confronted, is to lie. So telling a lie
to the question is a way of protecting ones self.
Regardless of the reason, when one tries to protect themselves, the
autonomous nervous system responds, causing changes in the body.
These changes are measurable and are recorded through the use of an
instrument called a polygraph.
If a guilty person
is attached to polygraph and is asked questions about the crime /
incident, they will lie to protect themselves from the consequences.
Because they are trying to protect themselves the autonomous nervous
system causes changes to take place, which are referred to as, deceptive
responses. If the same questions are being asked to an innocent
person, the person has nothing to protect themselves from. Therefore
notable difference in a deceptive persons responses and
non-deceptive person responses can be seen.
Can
Nervousness Affect the results?
Nervousness is a
completely normal feeling that one will experience when having to
undergo a polygraph test. Nervousness is a state that exists
throughout the test. Nervousness does not cause deceptive
responses....deception causes deceptive responses.
One must understand that a Polygraph Examination is a controlled
process in a suitable environment....and not an interrogation. The
Examiner also has a duty to explain the entire testing process and
the instrumentation to the person being tested. The Examiner must
set the environment and place the person at ease. Innocent people
tend to be cooperative and listen to the Examiner before the actual
test. They are therefore able to set their own minds at ease about
the process. For the guilty person, it does not matter, they are
usually hoping that the polygraph does not work or they are trying
to figure out a way of how to beat the test.
The Polygraph
Examination consist of 4 sections:
- Pre-test:
In this time the Examiner will explain the polygraph and the
physiology, the person rights, the case facts are discussed and a
consent form is signed..
- Test Phase:
This is when the person is attached to the instrument, the
questions are asked and the data is recorded. More than one chart
is always run.
- Chart
analysis: The Examiner will analyze the data and conclude the
outcome of the test. There are 4 possible outcomes.
- Post-test:
There are a number of variables that will determine this section
of the test. The person will however be informed of their test
result.
- Deception
Indicated - Person failed the test
- No Deception
Indicated - Person passed the test
- Inconclusive
- Unable to conclude a pass or fail result
- No Opinion
- This usually occurres when a person has been uncooperative
during the test phase and the data has been corrupted.
It is VERY
IMPORTANT to note that the Polygraph as an instrument does not
determine the accuracy or validity of the test. The Polygraph
instrument is just the recording device used during the process. It
records measurable changes in the body. Therefore there is no
accuracy or validity of the test results attached to the instrument.
The accuracy and validity are based entirely on the competency of
the Polygraph Examiner. It is therefore VERY IMPORTANT to only make
use of Examiners who have received internationally recognized
certified and accredited training. To be sure that you are using an
accredited and certified Polygraph Examiner, check the
Polygraph Association of South
Africa's (PASA) website for a listing of Examiners. Examiners at
the least should be a member of PASA and or the
American Polygraph Association
(APA)
