Background Theory Types Accuracy Polygraph

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 CQT DLT GKT Extremely poor 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 GKT Psychopathy/sociopathy 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

An actual CIT polygraph record

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