Chapter 19: Employing Polygraph Assessment

The polygraph instrument itself records autonomic nervous system responses including respiration, perspiration, and cardiovascular activity rather than detecting deception directly. Two primary applications exist: specific incident investigation and personnel screening. For incident investigations, the Control Question Technique compares physiological responses to crime-relevant questions against control questions designed to provoke anxiety about past behaviors, with the assumption that guilty individuals will show stronger reactions to relevant questions while innocent subjects react more to controls. The Guilty Knowledge Test instead assesses recognition of crime-specific details known only to perpetrators through a multiple-choice format without explicitly testing for dishonesty. Personnel screening employs the Relevant-Irrelevant Technique, alternating between potentially incriminating questions and neutral ones, though this method is methodologically problematic due to the inherent arousal difference between question types. Critical examination of research methodology reveals significant flaws in validity studies: laboratory investigations using mock crimes lack genuine fear of consequences, inflating accuracy estimates, while field studies suffer from confession bias wherein examiners interrogate only polygraph-failing subjects, artificially eliminating false positive rates from statistical analysis. When independent evidence establishes ground truth, Control Question Technique accuracy for innocent subjects approaches chance levels around fifty-seven percent, and guilty individuals can readily employ physical or cognitive countermeasures to defeat detection. Emerging technological alternatives include Event-Related Potential assessment measuring P300 brainwaves during recognition tasks, functional magnetic resonance imaging detecting prefrontal cortex activation during deceptive responses, thermal imaging identifying facial blood flow changes associated with stress, and voice stress analysis, though each approach faces similar vulnerabilities to countermeasures and alternative explanations for neural or physiological activation. Legal admissibility of polygraph evidence remains limited, typically requiring prior prosecution-defense stipulation or meeting Daubert scientific standards, with courts expressing concern that the instrument's scientific appearance may inappropriately influence jury decision-making. The psychological science community maintains substantial skepticism toward traditional polygraphy despite widespread use in law enforcement and security contexts, with continued application driven primarily by utility as a psychological pressure mechanism eliciting confessions and self-incriminating disclosures rather than demonstrated validity.