Graham Davies Week 5 Detecting Deception in Witnesses and Suspects

Sources of information Non-verbal behaviour (‘body language’) Paralinguistic cues Physiological measures Content of statement

Non-Verbal and Paralinguistic cues Embedded in Law (the Confrontation principle) ‘Leakage’, ‘manipulators’ and ‘micro expressions’ – Ekman (1993) But how good are people in practice?

Laboratory Studies on lie detection High confidence, high intergroup agreement – but chance performance (Vrij 1993) Police (54%) no better than public (50%) (DePaulo & Pfeifer, 1986) Even with longer extracts (Kohnken, 1987) ‘Truth bias’ (58% true vs 31% believed false)

Laboratory Studies on lie detection Custom’s Officials do no better (Kraut & Poe, 1980) But Secret Service Officers do better than Judges or Psychiatrists (Ekman & O’Sullivan, 1991) Are there skilled liars? (DePaulo & DePaulo, 1980)

Concerns over Ecological Realism Lying in high stakes situations (Vrij & Mann, 2001) Press conference appeals Chance performance by police officers Performance unrelated to age, experience or confidence

Why are people so poor at detecting deceptions? Lack of feedback ? Gap between actual and perceived cues The lens model Stress and lying: The ‘Othello’ error There is no Pinocchio test !

Physiological Measures: The Polygraph Measures: typically blood pressure, respiration, skin conductance Over 4000 polygraph technicians in the USA Used in criminal investigations, security screening in military and banking sectors Evidence admissible in 32 US States

Testing Techniques Guilty knowledge test (GKT) Control Question techniques (CQT) CQT most widely used in the USA GKT used in Israel

Laboratory Studies of the Polygraph (after Vrij, 2000) Mainly conducted using the CQT detected 73% of guilty suspects - 9% labelled ‘innocent’ Only 66% of innocent – 13% labelled ‘guilty’ False positive errors more common than false negative – reverse of body language Problems with laboratory studies

Field Studies of the Polygraph (after Vrij, 2000) Polygraph records of suspects subsequently proven to be innocent or guilty Classification by trained operators ‘blind’ to origins of record 87% of guilty suspects detected – 10% innocent 72% of innocent suspects detected – 21% believed to be guilty For GKT: 98% of innocent, but only 42% of guilty (Ben-Shakhar & Elaad, 2003)

Counter measures: Do they work? Tongue biting; foot tensing: to increase arousal to control questions Backward counting, erotic thoughts, to prevent processing of material ‘Buzz’ Faye taught lifers such techniques. 23 out of 27 able to pass CQT after 2 hours instruction (Ford, 1995)

Future Developments Computerised averaging and scoring (Raskin et al. 1988) - original examiners better than ‘blind’ - computerised scanning midway between ‘Brain Fingerprinting’ (P300)- but vulnerable to counter-measures(Soskins et al., 2004) Thermal signatures around the eyes (Pavladis, Eberhardt & Levine, 2002) - 83% of guilty; 90% of innocent - but very small sample Open to same objections as Polygraph

In conclusion The conclusion of Zuckerman et al (1981) still seems sound: “The assumption that non-verbal channels are more important in the communication of deception is simply not true”. Investigational vs evidential uses Content still the best guide, whether assessed through cross-examinations at court (English system) or formal analyses of witness statements (Continental system). Supported by the BPS statement on the Polygraph and lie-detection (2004)