The Lie-Detection Myth - Psychology Today

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The Lie-Detection Myth - Psychology Today Posted: 31 Oct 2019 12:34 AM PDT People have always aspired to develop strategies to distinguish liars from truth-tellers, and they firmly believe that this ambition will materialize. But contrary to the notion that it is simple to tell a liar by his facial expressions or body language, studies have shown that in most cases, the accuracy of such diagnoses is not much higher than chance. Similar findings have been obtained among professionals whose work requires such identifications (police officers, judges, psychiatrists, and polygraphists). This is why the idea of a lie-detection machine based on measuring physiological responses, perceived as non-voluntary, sparked the human imagination for a long time.  The modern polygraph (or "lie detector") is a tool that measures simultaneously a number of physiological responses—such as changes in skin conductance, heart rate, and respiration—to a series of questions presented to a suspect. Polygraph tests are used not only in the criminal context but also for security screening and personnel classification. The dominant polygraph method, called the "comparison question test" (CQT) is based on a comparison of responses to relevant questions of the "Did you do it?" variety (e.g., "Did you kill Mr. Jones?") to non-specific comparison questions (e.g., "Have you ever hurt anyone?") The main assumption behind this method is that the person who killed Mr. Jones will show greater physiological responses to the relevant questions than the comparison questions, while an innocent suspect of the murder will display the opposite pattern. This assumption—which is not supported by theory or by solid research—rests on shaky ground because these physiological responses are associated with many factors other than deception (e.g., emotional arousal, surprise, cognitive effort). Consequently, any real suspect of a murder, whether guilty or innocent, is likely to be more aroused by the relevant, crime-related question than by the unrelated comparison question. This implies that innocent suspects tested by this polygraph method may be misclassified, which contradicts the most important goal of a criminal investigation—protecting the innocent. In addition, the assumption that the physiological responses measured by the polygraph cannot be controlled has been refuted by research. With minimal training, guilty suspects can avoid being detected. Thus, the idea that a machine can detect deception and differentiate truthful from deceptive individuals is a myth, although unfortunately a very popular one. While physiological responses cannot reveal deception directly (as there is no such thing as a "Pinocchio response"), extensive research has revealed that we do respond physiologically and behaviorally when presented with significant information (e.g., when presented with our name compared to names of unfamiliar people). This well-known phenomenon has been utilized to develop a method, designed to detect concealed knowledge rather than deception, that can help differentiate guilty suspects from innocent ones. The suspect is presented with an item from the crime scene along with other similar items, unrelated to the crime. For example, in a murder case, suspects may be told: "If you killed Mr. Jones, you would know where in the house his body was found." Then several locations (e.g. bedroom, kitchen, etc.), one of which is correct, are presented serially while several physiological responses are monitored. For the guilty suspect, the correct location is highly significant and will, therefore, elicit enhanced responses, but for the innocent suspect, who has no knowledge of the crime scene, all locations are similar and will elicit similar responses.  This method, designed to detect concealed knowledge, can protect innocent suspects from wrongful incrimination. But to achieve this goal, it is crucial that the crime scene information remains concealed from the general public and from potential suspects. This is why the method was labeled "the concealed information test" (CIT). Critics of the CIT have argued that it is of very limited usage due to the difficulty of identifying critical crime-scene details and keeping them concealed. However, the extensive use of the CIT by the Japanese National Police challenges this criticism. Investigators may well benefit from science by adopting methods for memory detection, rather than lie-detection.

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