more than 15 years, Robert Hanssen led a double life.
In one life he was a 25-year veteran with the Federal Bureau of Investigation
(FBI) who had access to some of the nation's most-classified
information. In his other life, he allegedly was spying for
the Russian government. Hanssen's deception was finally
discovered, and in February 2001 he was arrested and later
pled guilty to 15 espionage-related charges. Spies are
probably the world's best liars, because they have to be, but
most of us practice deception on some level in our daily
lives, even if it's just telling a friend that his horrible
haircut "doesn't look that bad."
Photo courtesy Lafayette
Instrument An analog
polygraph instrument Most analog polygraphs are being
replaced by digital devices.
People tell lies and deceive others for many reasons. Most
often, lying is a defense mechanism used to avoid trouble with
the law, bosses or authority figures. Sometimes, you can tell
when someone's lying, but other times it may not be so easy.
Polygraphs, commonly called "lie detectors," are
instruments that monitor a person's physiological reactions.
These instruments do not, as their nickname suggests, detect
lies. They can only detect whether deceptive behavior is being
Do you think you can fool a polygraph machine and examiner?
In this edition of HowStuffWorks,
you'll learn how these instruments monitor your vital signs,
how a polygraph exam works and about the legalities of
Man vs. Machine A polygraph instrument is
basically a combination of medical devices that are used to
monitor changes occurring in the body. As a person is
questioned about a certain event or incident, the examiner
looks to see how the person's heart rate,
rate and electro-dermal
activity (sweatiness, in this case of the fingers) change
in comparison to normal levels. Fluctuations may indicate that
person is being deceptive, but exam results are open to
interpretation by the examiner.
Source: Lafayette Instrument Physiological responses recorded by a
Polygraph exams are most often associated with criminal
investigations, but there are other instances in which they
are used. You may one day be subject to a polygraph exam
before being hired for a job: Many government entities, and
some private-sector employers, will require or ask you to
undergo a polygraph exam prior to employment.
What do you
think about lie detectors? Are they bunk or the real
here to state your
examinations are designed to look for significant involuntary
responses going on in a person's body when that person is
subjected to stress, such as the stress associated with
deception. The exams are not able to specifically detect if a
person is lying, according to polygrapher Dr. Bob Lee,
executive director of operations at Axciton
Systems, a manufacturer of polygraph instruments. But
there are certain physiological responses that most of us
undergo when attempting to deceive another person. By asking
questions about a particular issue under investigation and
examining a subject's physiological reactions to those
questions, a polygraph examiner can determine if deceptive
behavior is being demonstrated.
Photo courtesy Lafayette
Instrument Today, most
polygraph exams are administered with digital equipment
The polygraph instrument has undergone a dramatic change in
the last decade. For many years, polygraphs were those
instruments that you see in the movies with little needles
scribbling lines on a single strip of scrolling paper. These
are called analog polygraphs. Today, most polygraph
tests are administered with digital equipment. The scrolling
paper has been replaced with sophisticated algorithms and computer
Photo courtesy Lafayette
Instrument Parts of a
polygraph that monitor physiological responses
When you sit down in the chair for a polygraph exam,
several tubes and wires are connected to your body in specific
locations to monitor your physiological activities. Deceptive
behavior is supposed to trigger certain physiological changes
that can be detected by a polygraph and a trained examiner,
who is sometimes called a forensic psychophysiologist
(FP). This examiner is looking for the amount of fluctuation
in certain physiological activities. Here's a list of
physiological activities that are monitored by the polygraph
and how they are monitored:
Respiratory rate - 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.
Blood pressure/heart rate - 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.
Galvanic skin resistance (GSR) - This is also
called electro-dermal activity, and is basically a
measure of the sweat on
your fingertips. The finger tips are one of the most porous
areas on the body and so are a good place to look for sweat.
The idea is that we sweat more when we are placed under
stress. Fingerplates, called galvanometers, 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.
Some polygraphs also record arm and leg movements. As the
examiner asks questions, signals from the sensors connected to
your body are recorded on a single strip of moving paper. You
will learn more about the examiner and the test itself later.
Voodoo or Valid Detractors of the polygraph
call lie detection a voodoo science, saying that polygraphs
are no more accurate at detecting lies than the flip of a
coin. "Despite claims of 'lie detector' examiners, there is no
machine that can detect lies," reads a statement from the American
Civil Liberties Union (ACLU). "The 'lie detector' does not
measure truth-telling; it measures changes in blood pressure,
breath rate and perspiration rate, but those physiological
changes can be triggered by a wide range of emotions."
What do you
think about lie detectors? Are they bunk or the real
here to state your
has been performing polygraph exams for 18 years, agrees that
polygraphs do not detect lies. "What has happened over the
years is that the media has dubbed this lie detection, and
that's what's clicked, but from a scientific perspective,
absolutely not. There's no such thing as lie detection. I
couldn't tell you what a lie looks like."
He does assert that polygraphs can detect deceptive
behavior even through the stress brought on by the exam
itself. "If the (forensic psychophysiologist) is properly
trained and has the experience, he can penetrate that. Through
the specific procedure that the FP will employ, anxiety will
not penetrate into it."
In the next section, you will learn more about who
polygraph examiners are and what makes them qualified to
conduct these examinations.
people who are being given a polygraph exam will employ
certain countermeasures in an attempt to beat the
instrument. There are Web sites and books that instruct
you on how to fool the polygraph. Here are just a few
examples of how people try to trick the device:
Antiperspirant on fingertips
Tacks placed in the shoe
Biting tongue, lip or cheek
The idea of countermeasures is to cause (or curtail)
a certain reaction that will skew the test's result. A
subject may attempt to have the same reaction to every
question so that the examiner cannot pick out the
deceptive responses. For example, some people will place
a tack in their shoe and press their foot down on the
tack after each question is asked. The idea is that the
physiological response to the tack may overpower the
physiological response to the question, causing the
response to each question to seem identical.
Polygraph Examiners There are only two
people in the room during a polygraph exam -- the person
conducting the exam and the subject being tested. Today, some
polygraph examiners prefer to be called forensic
psychophysiologists (FPs). Because polygraph examiners are
alone in the room with a test subject, his or her behavior
greatly influences the results of the exam.
"It's a very serious factor when someone is being accused
of a crime," Lee said. "See, I don't care about the deceptive
person. I'm looking for the innocent person. I'm their
advocate. I'm totally unbiased and neutral when that person
comes walking in. But as soon as I make that assessment that
there's no deception indicated, I immediately become their
The forensic psychophysiologist has several tasks in
performing a polygraph exam:
Setting up the polygraph and preparing the subject being
Profiling the test subject
Analyzing and evaluating test data
How the question is presented can greatly affect the
results of a polygraph exam. There are several variables that
an FP has to take into consideration, such as cultural and
religious beliefs. Some topics may, by their mere mention,
cause a specific reaction in the test subject that could be
misconstrued as deceptive behavior. The design of the question
affects the way the person processes the information and how
he or she responds.
Who's Qualified? There
are approximately 3,500 polygraph examiners in the United
States, 2,000 of which belong to a professional organization,
according to Dr. Frank Horvath, a Michigan State
University professor of criminal justice and a member of the
are limited in their use in the private sector, but they
are frequently used by the U.S. government. Here are
some entities and occasions that may call for the use of
National security (Central Intelligence Agency,
Federal Bureau of Investigation, National Security
Internal-affairs investigations of law enforcement
concerned about the credentials and qualifications of many
polygraph examiners in the United States who do not belong to
some sort of professional organization. Laws regarding
polygraph licensing vary from state to state, and there is no
government or private entity that controls polygraph
licensing. Horvath also feels that training of polygraph
examiners is inadequate.
"I just do not think the field is at the state where we
would say that any polygraph examiner is the equal of all
other polygraph examiners. That's just not so," Horvath said.
"We have a number of standardization problems in terms of
examiner qualifications that concern me enormously. You could
buy a polygraph [instrument] tomorrow and come to Michigan and
you wouldn't be able to practice here because we have a
rigorous licensing law, but you could move down to Ohio and
open a business tomorrow."
Today, some polygraph examiners take classes and work an
internship in order to become an accredited examiner with
national associations. Some states also require examiners to
be trained. There are many schools around the United States
that have been set up to train people to conduct polygraph
exams. One of these schools is the Axciton International
Academy, which was started by Lee. The school is
accredited by the American Polygraph Association and certified
by the American
Association of Police Polygraphists.
Here are the steps that students at the Axciton Academy
must complete before becoming licensed forensic
Prior to enrolling in the school, students must possess
a baccalaureate degree or have five years of investigative
experience and an associates degree.
Students must attend and pass a 10-week intensive
course. Curriculum includes psychology, physiology, ethics,
history, question construction, psychological analysis of
speech, chart analysis and test-data analysis.
Students must enter an internship program and conduct a
minimum of 25 exams for actual cases. These exams are
faculty reviewed. This internship can take anywhere from
eight months to one year.
Following the completion of these requirements, the student
becomes a polygrapher and may obtain a license in his or her
state if that state requires one. There is no standardized
test that all polygraph examiners must pass in order to
Going on the Box Undergoing a lie detector
test can be an intimidating experience that can challenge the
nerves of even the most stoical person. You are sitting there
with wires and tubes attached to and wrapped around your body.
Even if you have nothing to hide, you could be afraid that the
metal-box instrument sitting next to you will say otherwise.
Fittingly, undergoing the uncomfortable experience of a
polygraph test is often referred to as "going on the box."
Mouse-over the wire colors to
see where they lead.
A polygraph exam is a long process that can be divided up
into several stages. Here's how a typical exam might work:
Pretest - This consists of an interview between
the examiner and examinee, where the two individuals get to
learn about each other. This may last about one hour. At
this point, the examiner gets the examinee's side of the
story concerning the events under investigation. While the
subject is sitting there answering questions, the examiner
also profiles the examinee. The examiner wants to see how
the subject responds to questions and processes information.
Design questions - The examiner designs questions
that are specific to the issue under investigation and
reviews these questions with the subject.
In-test - The actual exam is given. The examiner
asks 10 or 11 questions, only three of four of which are
relevant to the issue or crime being investigated. The other
questions are control questions. A control question
is a very general question, such as "Have you ever stolen
anything in your life?" -- a type of question that is so
broad that almost no one can honestly respond with a "no."
If the person answers "no," the examiner can get an idea of
the reaction that the examinee demonstrates when being
Post-test - The examiner analyzes the data of
physiological responses and makes a determination regarding
whether the person has been deceptive. If there are
significant fluctuations that show up in the results, this
may signal that the subject has been deceptive, especially
if the person displayed similar responses to a question that
was asked repeatedly.
Whether you pass or fail a polygraph exam will often have
very little legal ramification. Often, defense lawyers brag
that their client has passed a polygraph. Of course, you will
rarely hear of a defendant taking a polygraph if he or she
failed it. In the next section, you will learn more about the
legalities of polygraph exams.
There are times
when a polygraph examiner misinterprets a person's
reaction to a particular question. The human factor of a
polygraph exam and the subjective nature of the test are
two reasons why polygraph exam results are seldom
admissible in court. Here are the two ways that a
response can be misinterpreted:
False positive - The response of a truthful
person is determined to be deceptive.
False negative - The response of a
deceptive person is determined to be truthful.
"If we look at laboratory-based studies,
false-positive errors occur somewhat more often than
false-negative errors," Horvath said.
Critics of polygraph exams say that even more
false-positive errors occur in real-world scenarios,
which biases the system against the truthful person.
These errors are likely to occur if the examiner has not
prepared the examinee properly or if the examiner
misreads the data following an
The Legalities of Polygraphs Polygraphs are
rarely admissible in court. New Mexico is the only state in
the United States that allows for open admissibility of
polygraph exam results. Every other state requires some type
of stipulation to be met prior to admitting polygraph exams
into record. In most cases, both sides of a legal case have to
agree prior to the trial that they will allow polygraphs to be
admitted. On the federal level, the admissibility criteria are
much more vague and admission typically depends on the
approval of the judge.
The main argument over the admissibility of polygraph tests
is based on their accuracy, or inaccuracy, depending on how
you want to view it. The level of accuracy of a lie detector
depends on who you talk to about it, Horvath said. Both sides
of the argument have the same research to look at, but they
come to very different conclusions.
"We have people in the scientific community who look at the
same research that I look at and they reach a conclusion that
is quite different," Horvath said. "From their point of view,
they allege that polygraph testing is probably only around 70
percent accurate, and it has a great bias against truthful
people. Then, what the proponents say, looking at the same
research, they reach a quite different conclusion, and that is
that polygraph testing is around 90 percent accurate."
Employee Polygraph Protection
Act of 1988
in the private sector are not subjected to polygraph
exams like employees of the federal government. The U.S.
federal government is the largest consumer of polygraph
exams. Private sector employees are protected by the
Employee Polygraph Protection Act of 1988 (EPPA). This
law only affects commercial businesses. It does not
apply to schools, prisons, other public agencies or some
businesses under contract with the federal government.
EPPA provides that a business cannot require a
pre-employment polygraph and cannot subject current
employees to polygraph exams. A business is allowed to
request an exam, but cannot force anyone to undergo a
test. If an employee refuses a suggested exam, the
business is not allowed discipline or discharge that
employee based on his or her
federal level, there have been specific legal cases that have
shaped the admissibility of polygraphs. The results of these
cases are mixed: There have been some federal circuits that
have admitted polygraph results, while others have flatly
denied them. Here are just a few of the legal cases that have
shaped how polygraphs are viewed by the U.S. courts:
Frye v. United States (1923) - U.S. Court of
Appeals of District of Columbia - This is the original
decision dealing with scientific evidence and its
admissibility in court. Frye was accused of murdering a
doctor. At the time, he took a unigraph, a precursor
to the polygraph. The unigraph measured only the
cardiovascular activities of the body. The examiner reported
Frye to be truthful, and Frye moved to have that evidence
admitted in court. The court ruled that before any
scientific evidence could be admitted into the court of law
it must first be accepted by the scientific community. At
that time, there were no studies done on unigraphs or
polygraphs, so the evidence was not admitted.
United States v. Piccinonna (1989) - U.S. Court
of Appeals, 11th Circuit - This decision allowed for
polygraph results to be admitted in court, but only if one
of two requirements is met: Either the two parties in the
case agree to allow it, or the judge decides to allow it
based on criteria established by the 11th Circuit.
Daubert v. Merrell Dow Pharmaceuticals (1993) -
U.S. Supreme Court - The court opened the door for
scientific evidence, and gave judges broader discretion as
to whether or not to admit polygraphs. This applies to all
federal courts but does not apply in state courts, although
particular states do accept this ruling.
United States v. Scheffer (1998) - U.S. Supreme
Court - Moving beyond the broader topic of scientific
evidence, this military case directly involved polygraphs.
The court ruled that the U.S. president has the prerogative
to deny polygraph results in military tribunals because
polygraph testing is so controversial.
It seems clear that no final decision has been made on the
federal level. At the state level, polygraph admissibility is
generally handled on a case-by-case basis. The courts'
ambiguity stems from the questionable validity of polygraph
exams. Interestingly, the biggest opponent to polygraph
admission in court is the U.S. federal government, which
happens to be the largest consumer of polygraphs exams.
There are still many questions that must be answered before
polygraphs are accepted by the courts and the public at large.
Of course, we may never see this broad acceptance. No matter
if you agree or disagree with the use of polygraphs, thousands
of people undergo these tests every year, and many people's
lives are changed forever by their results.