Polygraph
Background
Theory
Types
Accuracy
Physiological detection of deception
(PDD)
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Use physiological measurements as an index
of deception
Not behavioral
Directly measure arousal or other cognitive
processes
What is a polygraph?
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NOT a lie detector
Poly = many, graph = write
Machine that records multiple continuous
measures of autonomic nervous system
arousal
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Galvanic skin response (GSR)
Thoracic and abdominal respiration
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Respiration line length (RLL)
Blood Pressure
Heart rate
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Finger pulse waveform length
The “lie detector” refers more to the test
used
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Relevant/Irrelevant test
Rising Peak of Tension
Comparison Question Test
Directed Lie Test
Concealed Information Test
Polygraph - History

William Moulton Marston
(1893 – 1947)
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Student of Hugo Münsterberg
at Harvard
Discovered correlation
between blood pressure and
arousal during lying
Polygraph - History

John Augustus Larson

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Rookie police officer in the
Berkeley, CA, police
department
Ph.D. in physiology from UC


Read Marston’s article
“Physiological Possibilities of
the Deception Test”
Improved test through
continuous recording of
blood pressure
Polygraph – History (Larson, cont…)

First real-world application

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“Cardio-pneumo-psychograph”
Berkeley sorority house - 1921
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Items including an expensive ring had been stolen from rooms
Helen Graham
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“No sooner had he brought up the subject of the diamond ring and
stolen money – “The test shows you stole it. Did you spend it?” –
than Graham’s record showed a precipitous drop in blood
pressure before beginning what looked to be an alarming rise,
along with skipped heartbeats and an apparent halt in her
breathing.” – Alder, The Lie Detectors.
Married Margaret Taylor, one of the other suspects
Polygraph - History

Leonarde “Nard” Keeler
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Through connections with
Berkeley police chief, August
Vollmer, was introduced to
Larson (1930s)
Worked on developing his own
polygraph while “studying” at
Berkeley and UCLA
Created first polygraph school
in Chicago in 1948
Autonomic nervous system (ANS)

Part of the peripheral nervous system controlling
visceral or automatic functions

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Sympathetic and parasympathetic nervous systems
General theory behind polygraph

Arousal  Increased sympathetic nervous system activity
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Sweating
Respiration changes
Vasoconstriction
Pulse rate
Blood pressure
Specific patterns of arousal during questioning could
indicate guilt or lying
Polygraph – Modern version

Modern polygraphs are now computerized
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Allow for more accurate and automatic (unbiased) analysis
Main Measures
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Galvanic skin response (sweating)
Respiration
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Blood pressure
Pulse oximeter


Thoracic and Abdominal
Measures percentage of oxygenated hemoglobin
Pad(s) to measure subject movement
Polygraph – Relevant/Irrelevant Test
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Earliest method of polygraph testing
Two kinds of questions

Relevant
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Deal with issue at hand
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Irrelevant
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Deal with outside facts or details

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e.g. “Did you murder your wife?”
e.g. “Are you in a police station?”
Assumption:

A liar or guilty person will be more aroused by relevant
questions than Irrelevant ones, while an innocent person
will show no difference
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So, if arousal(relevant) > arousal(irrelevant) = lying
Polygraph – Searching Peak of Tension
(POT)
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Developed by Keeler
Can be used when specific details of a crime are unknown to the
investigator
Suspect is presented serially with potential relevant clues
 Areas in which a body may be located
 Amounts of money that may have been stolen
Assumption:
 A guilty person will react strongest when the correct alternative is
chosen
 An innocent person may simply become more aroused as the test
goes on, but will not show a significant sudden increase in
arousal to one alternative
Polygraph – Comparison Question Test

Most common method of polygraph
interrogation
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Developed by John Reid
Preferred method of polygraph
testing in the United States
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Used for four main purposes (National
Research Council, 2003)
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Criminal investigations
Pre-employment screening for law enforcement
and federal jobs with security clearances
Testing of sexual offenders in treatment, on
parole, or in prison
CQT Structure:
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1. Pre-interview phase
 obtain information about suspect and the crime
2. Stimulation test
 convinces examinee that the test works
 often use card test (similar to CIT)
3. Formulating question phase
 questions are discussed with examinee
 identify specific questions to ask
 prevents problems in interpretation
4. Test is given
5. Scoring
6. Confession
CQT Method:
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Three kinds of questions:
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1. Relevant
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2. Comparison (aka probable lie)
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E.g. “Have you ever physically harmed someone”
3. Irrelevant
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E.g. “Did you kill Nicole Brown Simpson”
Is your name Orenthal James Simpson?
Assumption:
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A liar become more aroused by lying to the relevant questions
than the comparison questions
An innocent person will be more aroused by the comparison
questions
Arousal(relevant) > Arousal(comparison) = guilty
Reid CQT (modified general questions test
(MGQT)
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Original CQT
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Accusatory interview
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Suspect is lectured on the importance of honesty
Uses comparison questions that are known to be deceptive
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Difficult to develop
Very general
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e.g. “Have you ever cheated anyone?”
Scoring is done globally (across whole test)
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Not systematic or standardized
Backster Zone Comparison Test (Backster
ZCT) – Backster (1963)
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Comparison questions renamed “probable-lie questions”
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Deal with acts similar to the issue being investigated
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Uses two relevant questions
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Similar wordings of same question
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e.g. “Did you rob the Kwik-E-Mart in Springfield?”
“Did you use a gun to rob Apu at the Kwik-E-Mart?
Comparison questions are very specific
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Still very general/vague
e.g. “Did you ever steal from a place you worked?”
Introduced numeric scoring system
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From -3 to +3 on each measure
Very complex and biased rules
Utah Probable Lie Test (PLT) – Raskin
group
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Professional, non-accusatory interview (~1 hr)
Adds stimulation test
All questions are reviewed with suspect
Changes nature of probable lie (comparison) questions:
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“Prior to college, did you ever tell anything dishonest to a teacher
or authority figure?”
Scoring
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-3 to 3 for each relevant/comparison question
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Positive if comparison > relevant
Negative if relevant > comparison
Non-standardized
Utah Directed Lie Test (DLT)
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Same kind of questions as CQT, only subject
is instructed to lie to all the comparison
questions
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Assumption:
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Guilty person will show more arousal lying to
relevant questions
Innocent person will show more arousal lying to
comparison questions
Example of questioning:
Question Type Question
N1
Do you live in Evanston?
Response
"Yes"
C1
During the first 18 years of your life, did you ever
cheat on an academic assignment?
"No"
R1
Did you cheat on the Deception midterm?
"No"
N2
Are you a psychology major?
"Yes"
C2
Prior to starting college, did you ever do anything
academically dishonest?
"No"
R2
Did you look at the answer sheet of the student
next to you during the midterm?
"No"
N3
Are you a student at Northwestern University?
"Yes
C3
Before starting college, did you ever copy
someone else's work?
"No"
R3
Did you in any way take answers from another
student on your exam?
"No"
CQT – Expected Results
6
Reactivity
5
4
3
Comparison
Relevant
2
1
0
Guilty
Innocent
Suspect
Polygraph Chart
Polygraph – Accuracy (Vrij, 2008)
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R/I
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Extremely poor
CQT
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83 - 89% for guilty subjects
53 – 75% for innocent subjects
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12 – 47% incorrectly classified (falsely accused of guilt)
DLT (Raskin & Honts, 2002)
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Guilty
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73 – 84% depending on type of directed lie
Innocent
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84 - 87%
CQT Problems (Ben-Shakhar, 2002)
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Five main issues:
1.
2.
3.
4.
5.
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Inadequate theoretical and logical rationale
Inadequate standardization
Lack of objective quantification procedures for physiological responses
Implications of contamination with other sources of information
Countermeasures
Psychopathy/Sociopathy
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Estimates as high as 20% of criminal population
Some evidence suggests this is not a problem

Patrick and Iacono (1989), Raskin and Hare (1978)
Methodological Problems
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Lack of incorporation of psychological
knowledge
Lack of standardization
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Interview, questioning, scoring
Deceptive nature of procedures
Polygraph – Problems (cont…)
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Countermeasures
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Methods used to defeat a test
Increase autonomic arousal
during certain questions
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Easy
Distraction techniques
Difficult to identify
Can be apply to any kind of
polygraph method
After 30 minutes of training,
~80% of subjects in a study by
Honts et al., 1994, beat a CQT
Polygraph – Problems (cont…)
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Admissibility in court
Daubert Standard
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1. Is the scientific hypothesis testable?
2. Has the proposition been tested?
3. Is there a known error rate?
4. Has the hypothesis and/or technique been
subjected to peer review and publication?
5. Is the theory upon which the hypothesis and/or
technique based generally accepted in the
appropriate scientific community?
Polygraph – So why is it still used?
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Effective at soliciting confessions
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General belief of the infallibility of the machine
“Psychological third-degree”
Employee Screening
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Can no longer be required due to Employee Polygraph
Protection Act of 1988
Polygraph – Famous misses
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Julius and Ethel
Rosenberg
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Passed nuclear secrets to
Soviet Union
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Aldrich Ames
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CIA officer
Convicted of spying for
Soviet Union
Additional Resources

A Tremor in the Blood –
David Lykken
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Handbook of Polygraph
Testing – Murray Kleiner

The Lie Detectors: The
History of an American
Obsession – Ken Alder
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Antipolygraph.org