Wherever two people communicate, deception is a reality. It is present in our everyday social and professional lives and its detection can be beneficial, not only to us individually but to our society as a whole. For example, accurate deception detection can aid law enforcement officers in solving a crime. It can also help border control agents to detect potentially dangerous individuals during routine screening interviews. Currently, the most successful and widespread system is the polygraph which monitors uncontrolled changes in heart rate and electro-dermal response, as a result of the subject’s arousal to deceit. Unfortunately, its widespread use does not necessarily mean it is a perfect system. Firstly, in order for it to take the necessary measurements, it needs to be continuously connected to the subject’s body. This means that the subject must be cooperative and in close proximity to the device. Secondly, it requires accurate calibration at the beginning of every session, so that a baseline of measurements can be established. Occasionally, it may still fail to give accurate readings, despite the calibration step; if for example, the subject’s heart rate increases for reasons unrelated to deception. Furthermore, the polygraph is an overt system, which means that the subject knows they are being monitored and also knows what measurements are being made. As a result, they may devise techniques to trick the machine, such as remaining calm, in an attempt to control their heart rate or being excited during the calibration phase, so that any excitement due to deception that the polygraph later registers, will mistakenly be regarded as a normal response. Lastly, the polygraph requires a trained operator, whose skills and abilities control both the likelihood of human error in the interview and the length of the interview itself. Unlike computers, humans will get tired and will eventually need a break. Therefore, what is needed is an automatic and covert system, which can continuously and unobtrusively detect deception, without requiring the subject’s cooperation. In response to this need, researchers have long been trying to decode human behavior, in an attempt to discover deceptive cues. These would aid them in designing systems for automatic deception detection or for training others to detect it. Some deceptive behaviors fall into one of two groups: over-control and agitation. In an attempt to hide their deception, liars who are aware of possible deceptive behavioral cues, may exert extra effort in hiding any behavior and particularly reducing movements of their hands, legs and head, while they are being deceptive. At the other extreme are liars who show signs of agitated behavior triggered by nervousness and fear. As a result, their speech tends to be faster and or they may engage in undirected dieting. Nevertheless, it is incorrect to assume that agitated or over-controlled behavior is always a sign of deception. One should also consider the normal behavior of a person, as well as the tone and context of the communication taking place. It may be the case that some subjects have a tendency of behaving over-controlled when interrogated by strangers. Others may seem agitated during an interrogation because they had just returned from their morning jog. According to Burgoon’s Expectancy Violations Theory (EVT), if in a communication there is considerable deviation of the observed behavior from the expected behavior, then this is a cause for suspicion. For example, an interrogator may become suspicious of a suspect who is relaxed at the beginning of the interrogation but becomes agitated as soon as they are questioned about a crime. Furthermore, in their Interpersonal Deception Theory (IDT), Buller and Burgoon state that deception is a dynamic process, whereby liars adjust their behavior according to how much they believe they are suspected of being deceitful. It is likely...
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