|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.
Choose one of the following topics below to read
to the polygraph
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
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.
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.
To The Polygraph
|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.
|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.
|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.