Introduction and uses of Polygraph in life.ppt

About polygraph

1. Polygraph
Background
Theory
Types
Accuracy

2. Physiological detection of deception
(PDD)
Use physiological measurements as an index
of deception
Not behavioral
Directly measure arousal or other cognitive
processes

3. What is a polygraph?
NOT a lie detector
Poly = many, graph = write
Machine that records multiple continuous
measures of autonomic nervous system
arousal

Galvanic skin response (GSR)

Thoracic and abdominal respiration

Blood Pressure

Heart rate

4. The “lie detector” refers more to the test
used
Relevant/Irrelevant test
Rising Peak of Tension
Comparison Question Test
Directed Lie Test
Concealed Information Test

5. Polygraph - History
William Moulton Marston
(1893 – 1947)

Student of Hugo Münsterberg
at Harvard

Discovered correlation
between blood pressure and
arousal during lying

6. Polygraph - History
John Augustus Larson

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

7. Polygraph – History (Larson, cont…)
First real-world application

“Cardio-pneumo-psychograph”

Berkeley sorority house - 1921
Items including an expensive ring had been stolen from rooms
Helen Graham
“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

8. Polygraph - History
Leonarde “Nard” Keeler

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

9. Autonomic nervous system (ANS)
Part of the peripheral nervous system controlling
visceral or automatic functions
Sympathetic and parasympathetic nervous systems
General theory behind polygraph
Arousal  Increased ANS activity
Sweating
Respiration changes
Vasoconstriction
Pulse rate
Blood pressure
Specific patterns of arousal during questioning could
indicate guilt or lying

10. Polygraph – Modern version
Modern polygraphs are now computerized

Allow for more accurate and automatic (unbiased) analysis
Main Measures

Galvanic skin response (sweating)

Respiration
Thoracic and Abdominal

Blood pressure

Pulse oximeter
Measures percentage of oxygenated hemoglobin

Pad(s) to measure subject movement

11. Polygraph – Relevant/Irrelevant Test
Earliest method of polygraph testing
Two kinds of questions
Relevant
Deal with issue at hand
Irrelevant
Deal with outside facts or details
Assumption:
A liar or guilty person will be more aroused by relevant
questions than Irrelevant ones, while an innocent person
will show no difference

So, if arousal
(relevant) > arousal
(irrelevant) = lying

12. Polygraph – Searching Peak of Tension
(POT)
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

13. Polygraph – Comparison Question Test
Most common method of polygraph interrogation

Developed by John Reid
Begins with extensive pre-test interview
Three kinds of questions:

1. Relevant

E.g. “Did you kill Nicole Brown Simpson”

2. Comparison (aka probable lie)
E.g. “Have you ever physically harmed someone”

3. Irrelevant

Is your name Orenthal James Simpson?

14. Polygraph – CQT (cont…)

Assumption:

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:

Criminal investigations

Employee screening

Security clearances

15. Polygraph – Directed Lie Test (DLT)
Same kind of questions as CQT, only subject
is instructed to lie to all the comparison
questions

Assumption:

Guilty person will show more arousal lying to
relevant questions

Innocent person will show more arousal lying to
comparison questions

16. Polygraph – Concealed Information Test
(CIT)

AKA – Guilty Knowledge Test (GKT)

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

“What was the weapon used to kill Mr. Boddy?”

Candlestick

Rope

Revolver
Lead Pipe

Knife

Wrench

Assumption:

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

17. Polygraph – CIT (cont…)
Lykken advocates 4 – 6 questions with 4 – 6
multiple-choice answers in each
Reduces theoretical false positive rate with
addition of each question
1/5 > 1/25 > 1/125, etc…
Scoring
2 points if Probe is largest, 1 if second largest
Total up points at the end
For 6 questions, 12 is perfect score
Lykken used cutoff of 7

18. Polygraph - Accuracy

R/I

Extremely poor

CQT

83 - 89% for guilty subjects

53 – 75% for innocent subjects

12 – 47% incorrectly classified (falsely accused of guilt)

DLT

One study, 80% correct

GKT

76 – 88% of guilty subjects

12 – 24% false-negatives

94 – 99% for innocent subjects

1 – 6% false-positives

19. Polygraph - Problems
CQT
Based on faulty theory
High false-positive rate
Biased
GKT
Difficult to create enough good GKT questions
Not applicable in every setting
Psychopathy/sociopathy
Estimates as high as 20% of criminal population

20. Polygraph – Problems (cont…)

Countermeasures

Methods used to defeat a test

Increase autonomic arousal
during certain questions

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

21. Polygraph – Problems (cont…)
Admissibility in court
Daubert Standard
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?

22. Polygraph – So why is it still used?
Effective at soliciting confessions

General belief of the infallibility of the machine

“Psychological third-degree”
Employee Screening

Can no longer be required due to Employee
Polygraph Protection Act of 1988

23. Polygraph – Famous misses
Julius and Ethel
Rosenberg

Passed nuclear secrets to
Soviet Union
Aldrich Ames

CIA officer

Convicted of spying for
Soviet Union

24. An actual CIT polygraph record

25. Additional Resources
A Tremor in the Blood –
David Lykken
Handbook of Polygraph
Testing – Murray Kleiner
The Lie Detectors: The
History of an American
Obsession – Ken Alder
Antipolygraph.org