Presentation on theme: "Detecting Deception Chapter 11. Detecting Deception Lying & deception as a consistent feature of human behavior “Santa Claus” People in general."— Presentation transcript:
Detecting Deception Lying & deception as a consistent feature of human behavior “Santa Claus” People in general are poor lie detectors Only slightly better than chance (exception is secret service agents)
Introduction Deception is a serious concern for accuracy in assessment and diagnosis in forensic and clinical settings. Meta-analytic literature fails to identify any pattern of facial or body movement that generally signals deception. But, some studies show some ability to discriminate lying from truth-telling; suggesting that the right measures of facial & motion features can offer accuracy better than chance for the detection of deception from demeanor in somewhat realistic situations.
Facial/Body Cues to Deception? Implicit assumption that liars will be more nervous & will betray themselves through unconscious actions Avoiding eye contact More smiling and laughter Higher rate of eye blinking Nervous fidgeting More illustrative gestures More movement of legs, feet, hands More body, head movements More shrugging
Deception Detecting Technology Polygraph Method Based on the belief that deception is related to physiological change Measures (arousal): Respiration Heart rate Sweating
Uses of Polygraph Helps in criminal investigations (suspect is asked to take a polygraph test) Verify a crime has occurred (victim is asked to take a polygraph test) Monitoring sexual offenders on probation (United States) Pre-employment screening for security agencies and police
Types of Polygraph Tests There are three main types of polygraph tests: Control Question Test (CQT) Guilty Knowledge Test (GKT)
Guilty Knowledge Test Assesses if suspect has information that only the criminal would know Asks suspects multiple choice questions, one option is correct Assumes if the suspect is guilty they will react strongly to correct information Not used in Canada or United States
Control Question Test Deception is assessed by comparing arousal levels of relevant and control questions The CQT begins with a pre-test interview: Control questions are developed Examiner attempts to convince the suspect of the accuracy of the polygraph Test phase includes three types of questions: irrelevant, relevant, and control If a suspect is believed deceptive they are pressured to confess
CQTest: Sample Questions Control Deal with prior behavior. Designed to provoke anxiety. General, non- specific misconducts used to establish a baseline lie Before age 25, did you ever verbally threaten to hurt anyone? Irrelevant Neutral issues that both guilty & innocent examinees are expected to tell truth about by answering ‘yes’ Baseline for truth Are you left- handed? Relevant Deal with the crime being investigated Did you assault Sam Smith the evening of November 11 th ?
CQTest Deception is assessed by comparing arousal levels of relevant & control questions Assumes guilty people react more to relevant questions and innocent people react more to control questions Innocent suspects assumed to react more to control questions than relevant questions Suspect falsely accused of a crime might react more strongly to questions about the crime than to vague questions concerning past behaviour
Countermeasures Both physical and mental countermeasures dramatically reduce the effectiveness of the CQT Examples??
Admissibility of Polygraph Not admissible into evidence in Canadian courts (R. v. Beland, 1987)
Other Measures for Lie Detection Voice stress analysis (VSA) Thermal imaging: Detects facial warming due to blood flow Brain-based measures: Event-related brain potentials (ERP) Electrodes measure brain activity in response to a significant stimulus P300 used to detect guilty knowledge
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