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
Blood Pressure
Heart rate
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
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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
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John Augustus Larson
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Rookie police officer in the
Berkeley, CA, police
department
Ph.D. in physiology from UC
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Read Marston’s article
“Physiological Possibilities of
the Deception Test”
Improved test through
continuous recording of
blood pressure
Polygraph – History (Larson, cont…)
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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
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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)
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Part of the peripheral nervous system controlling
visceral or automatic functions
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Sympathetic and parasympathetic nervous systems
General theory behind polygraph
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Arousal  Increased ANS 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
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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
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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
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Relevant
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Irrelevant
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Deal with issue at hand
Deal with outside facts or details
Assumption:
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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
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Most common method of polygraph interrogation
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Developed by John Reid
Begins with extensive pre-test interview
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. “Did you kill Nicole Brown Simpson”
E.g. “Have you ever physically harmed someone”
3. Irrelevant
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Is your name Orenthal James Simpson?
Polygraph – CQT (cont…)
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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
Uses:
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Criminal investigations
Employee screening
Security clearances
Polygraph – 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
Polygraph – Concealed Information Test
(CIT)
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AKA – Guilty Knowledge Test (GKT)
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Developed by David Lykken in 1958
Rather than trying to detect arousal caused by lying, tries to detect arousal from
recognition of “guilty knowledge” from the “orienting response”
Multiple-choice (serially presented) questions where the investigator knows the
correct answer
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“What was the weapon used to kill Mr. Boddy?”
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Candlestick
Rope
Revolver
Lead Pipe
Knife
Wrench
Assumption:
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A guilty person’s arousal will increase upon recognizing the correct alternative due to
involuntary orienting response
Innocent person will not be able to discern the correct alternative from the others
Polygraph – CIT (cont…)
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Lykken advocates 4 – 6 questions with 4 – 6
multiple-choice answers in each
Reduces theoretical false positive rate with
addition of each question
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1/5 > 1/25 > 1/125, etc…
Scoring
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2 points if Probe is largest, 1 if second largest
Total up points at the end
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For 6 questions, 12 is perfect score
Lykken used cutoff of 7
Polygraph - Accuracy
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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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DLT
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12 – 47% incorrectly classified (falsely accused of guilt)
One study, 80% correct
GKT
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76 – 88% of guilty subjects
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12 – 24% false-negatives
94 – 99% for innocent subjects
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1 – 6% false-positives
Polygraph - Problems
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CQT
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GKT
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Based on faulty theory
High false-positive rate
Biased
Difficult to create enough good GKT questions
Not applicable in every setting
Psychopathy/sociopathy
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Estimates as high as 20% of criminal population
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
An actual CIT polygraph record
Additional Resources
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A Tremor in the Blood –
David Lykken
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Handbook of Polygraph
Testing – Murray Kleiner
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The Lie Detectors: The
History of an American
Obsession – Ken Alder
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Antipolygraph.org