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Polygraph. Background Theory Types Accuracy. 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

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polygraph

Polygraph

Background

Theory

Types

Accuracy

physiological detection of deception pdd
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
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
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
Polygraph - History
  • William Moulton Marston (1893 – 1947)
    • Student of Hugo Münsterberg at Harvard
    • Discovered correlation between blood pressure and arousal during lying
polygraph history6
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
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 history8
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
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
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
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
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
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
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
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
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
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
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
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
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 cont21
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
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
Polygraph – Famous misses
  • Julius and Ethel Rosenberg
    • Passed nuclear secrets to Soviet Union
  • Aldrich Ames
    • CIA officer
    • Convicted of spying for Soviet Union
additional resources
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