Physiological detection of deception (PDD) Use physiological measurements as an index
of deception Not behavioral Directly measure arousal or other cognitive
processes
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
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
Polygraph - History
William Moulton Marston (1893 – 1947) Student of Hugo Münsterberg
at Harvard Discovered correlation
between blood pressure and arousal during lying
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
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
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
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
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
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
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
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?
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
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
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
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
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
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
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
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?
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
Polygraph – Famous misses
Julius and Ethel Rosenberg Passed nuclear secrets to
Soviet Union
Aldrich Ames CIA officer Convicted of spying for
Soviet Union