Imagine you are asked to give a lecture to a group of police officers about lie detection.Discuss what points you would focus on concerning reliable nonverbal and verbal cues to deception,the polygraph (including the guilty knowledge test),brain scans,and integrity tests.

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--Nonverbal and verbal cues.When researchers ask people to lie about something,like whether they enjoyed watching a gruesome film,their illustrators tend to decrease,whereas their manipulators and emblems tend to increase (Ekman,2001).Yet none of these gestures are foolproof indicators of dishonesty,so we shouldn't place too much stock in any one of them.Indeed,despite what most police officers believe,nonverbal cues tend to be less valid indicators of lying than verbal cues (Vrij,2008).The best way of finding out whether someone is lying is to listen to what they're saying rather than how they're saying it;for example,dishonest statements tend to contain fewer details and fewer qualifiers (such as "I'm not sure about this,but I think that …")than do truthful statements.
--The polygraph test.The polygraph or "lie-detector" test has long been one of the icons of popular psychology.The polygraph test,like most lie-detection techniques,rests on the assumption of the Pinocchio response: a perfect physiological or behavioural indicator of lying.Like Pinocchio's nose,people's bodily reactions supposedly give them away whenever they lie.Although the polygraph test usually does better than chance for detecting lies,it yields a high rate of false positives-that is,innocent individuals whom the test labels incorrectly as guilty.Putting it less technically,the polygraph test is biased against the innocent.Studies comparing the test results of known criminals with those of known noncriminals show that the test misclassifies a large proportion of innocent individuals (perhaps 40 percent or more)as guilty.The problem is that the polygraph test confuses arousal with evidence of guilt.The polygraph test is misnamed: It's an "arousal detector," not a lie detector.Many people display arousal following relevant questions for reasons other than the anxiety associated with lying,such as the fear of being convicted for a crime they didn't commit.Polygraph enthusiasts' claims to the contrary,there is no Pinocchio response,at least none that psychologists have discovered.The polygraph test may also yield a nontrivial number of false negatives-that is,guilty individuals whom the test incorrectly labels innocent.Many properly trained subjects can "beat" the test by using countermeasures-methods designed to alter their responses to control questions.
--Guilty knowledge testTo get around the polygraph test's shortcomings,David Lykken developed the guilty knowledge test (GKT),which relies on the premise that criminals harbour concealed knowledge about the crime that innocent people don't (Lykken,1959,1960).In contrast to the polygraph,the GKT doesn't hinge on the assumption of a Pinocchio response because it measures only suspects' recognition of concealed knowledge,not lying.In contrast to the polygraph,the GKT has a low false-positive rate-that is,it misidentifies few innocent people as guilty.In this respect,it may be a useful investigative device for law enforcement officials.Nevertheless,the GKT has a fairly high false-negative rate because many criminals may have either not noticed or since forgotten key aspects of the crime scene (Ben-Shakhar & Elaad,2003;Iacono & Patrick,2006).
--Tests using brain scanning techniques.Several researchers have attempted to improve on the traditional GKT by measuring suspects' brain waves following each item,a technique called brain fingerprinting.Brain waves may be a more sensitive measure of the recognition of concealed knowledge than skin conductance or other indices used in the traditional GKT.Nevertheless,the scientific support for brain fingerprinting is preliminary.One problem is that most of the evidence for this technique comes from laboratory studies in which participants are forced to rehearse details of a simulated crime (like the colour of a stolen purse or the type of jacket worn by a victim).In the real world,many criminals may forget these details,leading to lower accuracy rates.
--Integrity tests.Rather than use complex equipment designed to measure people's physiological responses,some employers administer paper-and-pencil integrity tests,questionnaires that presumably assess workers' tendency to steal or cheat.Integrity test questions fall into several categories,including potential employees': History of stealing ("Have you ever stolen anything from your place of work?");Attitudes toward stealing ("Do you think that workers who steal property from a store should always be fired?");Perceptions of others' honesty ("Do you believe that most people steal from their companies every now and then?").Integrity tests predict employee theft,absenteeism,and other workplace misbehaviour at better-than-chance levels.Yet these tests yield numerous false positives.So integrity tests,like the polygraph,may be biased against the innocent.

Imagine You Are Asked to Give a Lecture to a Group