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| Subconscious evidence
refers to the details investigators are able to deduce
from a suspect's subconscious
actions. Such evidence is not solid, but are useful
guidelines for determining someone's emotions/honesty
during an interview. |
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Choose one
of the following topics below to read more:
--> Polygraph
testing
--> Lying
to the polygraph
--> Other
testing methods
--> Body
language
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| Polygraph
Testing |
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When
police are interviewing suspects, it is often difficult
to spot if someone is lying or not. The invention, created
in the 1920's, known as the polygraph,
has proved a very useful tool during interviews for
police investigations. |
| *An
electronic polygraph machine is pictured left. Photo
courtesy of How
Stuff Works. |
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Polygraph
testing is used to measure the body's response to
stress. It involves a pair of plates that are attached
to the suspect's fingers. These are for measuring
the skin's resistance or sweat levels. Rises in blood
pressure and the speeding up of the pulse rate indicate
stress. A sphygmomanometer
is placed around the suspect's arm to measure these
levels. Heavy breathing represents anxiety and is
measured using pneumographs
wrapped around the chest. All of these test results
are recorded by the computer along with the questions
that caused the response.
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| Lying
To The Polygraph |
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| Though it may seem like
the polygraph test could never be incorrect, many of
the subject's responses are not clear. There are many
reasons for this including alcohol and drug use and
even hunger, which also affect the results. Pathological
liars have their own methods of cheating the machine,
including simple pain inflicting techniques such as
biting their tongue. By inflicting pain on themselves,
this affects the results on the machine. The fear and
anticipation of having to undergo one of these polygraph
tests also affects the results. Investigators often
only have to threaten the use the polygraph test, also
known as a 'lie-detector', for the person to change
their guilty/innocent plea out of fear. |
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| Other
Testing Methods |
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| Where the polygraph
tests have failed to reveal the truth, newer technologies
have stepped in with the answers. One new method involves
testing the electrical currents that move through our
brains when we think using a machine known as an electroencephalograph.
Researchers who work with this technology focus on one
wave in particular, the P300, or the wave that surges
when we see something we recognise or remember. The
P300 is monitored by showing the suspect pictures and
words not associated with the crime scene and then showing
them pictures of or relating to, the crime scene. When
the suspect recognises the crime scene, there is no
way of cheating, as you can't stop yourself from reacting
to familiar things. When falsely accused, the suspect's
brain waves will stay the same throughout the entire
process. |
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| Body
Language |
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| A suspect's
body language, mannerisms and gestures can often tell
police when a suspect is lying to them. For example,
children often cover their mouths after lying and in
adults; they often touch their chin after lying. Suspects
fiddling with their hands, watch or sleeve cuffs is
thought to be a disguised crossing of the arms, another
method which prevents them from expressing what really
happened. |
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| *Guestures,
expressions and in particularly, hand fiddling, are
all closely observed by police. Photo courtesy of www.morguefile.com.
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