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Polygraph

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

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  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 • Respiration line length (RLL) • Blood Pressure • Heart rate • Finger pulse waveform length

  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 sympathetic nervous system 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 • e.g. “Did you murder your wife?” • Irrelevant • Deal with outside facts or details • 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 • 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 • Preferred method of polygraph testing in the United States • Used for four main purposes (National Research Council, 2003) • 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

  14. CQT Structure: • 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

  15. CQT Method: • 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? • 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

  16. Reid CQT (modified general questions test (MGQT) • Original CQT • Accusatory interview • Suspect is lectured on the importance of honesty • Uses comparison questions that are known to be deceptive • Difficult to develop • Very general • e.g. “Have you ever cheated anyone?” • Scoring is done globally (across whole test) • Not systematic or standardized

  17. Backster Zone Comparison Test (Backster ZCT) – Backster (1963) • Comparison questions renamed “probable-lie questions” • Deal with acts similar to the issue being investigated • Still very general/vague • Uses two relevant questions • Similar wordings of same question • 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 • e.g. “Did you ever steal from a place you worked?” • Introduced numeric scoring system • From -3 to +3 on each measure • Very complex and biased rules

  18. Utah Probable Lie Test (PLT) – Raskin group • Professional, non-accusatory interview (~1 hr) • Adds stimulation test • All questions are reviewed with suspect • Changes nature of probable lie (comparison) questions: • “Prior to college, did you ever tell anything dishonest to a teacher or authority figure?” • Scoring • -3 to 3 for each relevant/comparison question • Positive if comparison > relevant • Negative if relevant > comparison • Non-standardized

  19. Utah 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

  20. Example of questioning:

  21. CQT – Expected Results

  22. Polygraph Chart

  23. Polygraph – Accuracy (Vrij, 2008) • R/I • Extremely poor • CQT • 83 - 89% for guilty subjects • 53 – 75% for innocent subjects • 12 – 47% incorrectly classified (falsely accused of guilt) • DLT (Raskin & Honts, 2002) • Guilty • 73 – 84% depending on type of directed lie • Innocent • 84 - 87%

  24. CQT Problems (Ben-Shakhar, 2002) • Five main issues: • 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 • Estimates as high as 20% of criminal population • Some evidence suggests this is not a problem • Patrick and Iacono (1989), Raskin and Hare (1978)

  25. Methodological Problems • Lack of incorporation of psychological knowledge • Lack of standardization • Interview, questioning, scoring • Deceptive nature of procedures

  26. 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

  27. 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?

  28. 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

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

  30. 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

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