Remember to also read our article on the controversy of whether we should use polygraph evidence in court!
Deception – a deliberate attempt to misinform another – is a common and important aspect of human communication. On average, we lie twice daily and deceive others across face-to-face, email and phone conversations. Often, the lies we tell are minor and grease the wheels of social interaction. The astute husband quickly learns that there is only one appropriate answer to the question, “Does this dress make me look fat?” despite the reality of his wife’s appearance. However, lies can also be self-serving, potentially consequential, and at odds with the justice system. Despite the frequency of lies in our daily interactions, humans are poor deception detectors. In general, people (relevant legal professionals, included) are highly confident in their ability to suss out the liars, but rarely perform above the level of chance (50%).
Poor lie detection accuracy is likely related to a reliance on invalid cues to deception, human biases and over-confidence, leading to uncritical decisions about credibility. Despite popular belief the world over, liars do not avert their gaze more than truth-tellers and far from being common sense, deception detection is a difficult task. Further, irrelevant first impressions can lead our decisions about deception astray. For example, attractive people are generally considered good, trustworthy, and honest. Indeed, attractive people are less often labeled as liars by highly confident but incorrect decision-makers.
Although lie detection is a difficult task, lying too is a taxing exercise. The liar must suppress the truth, create a coherent and plausible story while maintaining facial expression, speech and body language, consistent with the false message. The difficulty of this necessary multi-tasking provides several opportunities to detect signals of the liar’s emotional arousal, heavy cognitive load, and impression management techniques.
Liars may feel nervous, guilty or even delighted while pulling the wool over your eyes. As such, physiological arousal may indicate deception. However, it is not inconceivable that an anxious innocent suspect, when asked about his or her involvement in a murder, may show similar increases in heart rate, blood pressure and skin conductance. Thus, reliance on physiological measures alone can lead to false alarms. Indeed, this is a major drawback of the polygraph. Emotional arousal experienced by the liar (or truth-teller) can be examined more specifically by careful attention to the face which may provide indications of falsified emotions and leakage of genuine ones. On a related note, liars may try to distance themselves from their message, linguistically (i.e., by choosing particular words to say), to decrease their emotional arousal. While this tactic may make lying easier it leaves linguistic footprints on the liar’s narrative, including fewer emotional words, pronouns and more tentative language.
The act of lying is more mentally-taxing than telling the truth; while truth-tellers simply relay their memory for the events in question, the liar must create details that make sense and do not contradict what the receiver knows to be true. This idea is supported by functional brain imaging research which has found that lying is related to increased prefrontal lobe activation than truth-telling, a brain area used for higher-order thinking. As a result of this heavy cognitive burden, liars may use fewer words, speak slower, pause longer and hesitate more (using ‘ums’, ‘ahs’ and ‘ers’) than genuine individuals. Liars narratives also may include less context and fewer reproduced conversations; details that are a part of (truthful) memories but are difficult to create from imagination. Cognitive load may also result in a decrease in blink rate and a neglect of normal body language, leading to the use of fewer illustrators (hand movements that accompany speech). Recently, active attempts to increase cognitive load in interview settings has led to greater behavioural differences between genuine and deceptive interviewees. For example, asking the interviewee to describe the events in question in reverse-order led to intensified signals of cognitive load, in particular for liars.
Lastly, liars may attempt to control their behavior to avoid being viewed as deceptive. In contrast, liars tend to take their credibility for granted and behave more naturally. As liars try to manage the impression that they make upon their interviewer, they may overcompensate. For example, knowing that may people believe gaze aversion and fidgeting to be related to deception, the liar may stare too intently and overly constrict their body movements to avoid making an untrustworthy impression. This pattern, however, may differ across individuals; practiced liars may actually show an increase in body movements, producing non-verbal behavior that distracts the interviewer from the content of the lie. In general, it is helpful to have a baseline of the interviewee’s behavior; knowing how the person behaves when he or she is being truthful can help in identifying when behavior changes, potentially signaling deception.
Although deception detection is a difficult task, it can be learned. Training programs that have focused on dispelling the myths about deception detection and provided empirically-valid knowledge about behavioural cues to deceit have proven successful. Active interviewing strategies also provide opportunities for the lie detector. While there is no Pinocchio’s nose – no perfect indicator of deception – an understanding of the behavioural consequences of lying can assist the lie catcher.
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