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Polygraph Background Theory Types Accuracy. Physiological detection of deception (PDD) Use physiological measurements as an index of deception Not behavioral.

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Presentation on theme: "Polygraph Background Theory Types Accuracy. Physiological detection of deception (PDD) Use physiological measurements as an index of deception Not behavioral."— Presentation transcript:

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 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: Question TypeQuestionResponse N1Do you live in Evanston?"Yes" C1 During the first 18 years of your life, did you ever cheat on an academic assignment? "No" R1Did you cheat on the Deception midterm?"No" N2Are you a psychology major?"Yes" C2 Prior to starting college, did you ever do anything academically dishonest? "No" R2 Did you look at the answer sheet of the student next to you during the midterm? "No" N3Are you a student at Northwestern University?"Yes C3 Before starting college, did you ever copy someone else's work? "No" R3 Did you in any way take answers from another student on your exam? "No"

21 CQT – Expected Results

22 Polygraph Chart

23 Polygraph – Accuracy (Vrij, 2008) R/I  Extremely poor CQT  % 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 %

24 CQT Problems (Ben-Shakhar, 2002) Five main issues: 1.Inadequate theoretical and logical rationale 2.Inadequate standardization 3.Lack of objective quantification procedures for physiological responses 4.Implications of contamination with other sources of information 5.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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