Detecting Guilty Knowledge 1 Running Head: GUILTY KNOWLEDGE DETECTION AND THE N400 Detecting Guilty Knowledge: The N400 Component of Event-Related Potentials

Traditional methods of lie detection, especially the polygraph, often result in fault positives and the use of countermeasures. This study explores novel techniques of detecting guilty knowledge that employ the use of the N400 component of event-related potentials (ERPs). This new method of assessing credibility is not reliant on verbal testimony or emotional responses as the polygraph is. Participants in this study were randomly assigned to either a mock crime or innocent condition. Both conditions were presented with a series of sentences as part of the experimental design. In some instances, the terminal words of these sentences were specifically designed to elicit a N400 for those who committed the mock crime. ERP averages for the sentences were analyzed using a statistical bootstrap technique, wherein ten new averages were created for each participant. The resulting ERP averages were correlated and examined in an effort to develop an individual classification system for the detection of guilty knowledge. Detecting Guilty Knowledge 3 Detecting Guilty Knowledge: The N400 Component of Event-Related Potentials The most common method of lie detection used by the justice system is the polygraph. This method of detecting deception is based on the assumption that when questioned, a guilty person will exhibit autonomic arousal if lying (Bashore and Rapp, 1993). Thus, the polygraph is designed to measure changes in physiological processes such as respiration, skin conductance, heart rate and blood pressure in an effort to determine if the recorded pattern of arousal is consistent with that of a person who is known to be lying (Lykken, 1981). Therefore, the polygraph allows for an individual classification system of guilt. There are however, several problems that have been suggested by critics of traditional polygraph use. These criticisms include the unacceptably large number of false positives that are yielded by the polygraph; that is, the large number of innocent people that are found to be guilty (Boaz, Perry, Raney, Fischler & Shuman, 1991). The use of countermeasures also suggests a problem with the polygraph. Because the polygraph relies on a change in autonomic arousal, if the subject is lying and he or she can control arousal by using tranquilizers or even systematic muscle tension, they could potentially escape detection if they are guilty. Despite the obvious problems that are inherent in the use of the traditional polygraph, it has acquired some respect because of its development of an individual classification system. The most desirable assessment test that is used in conjunction with the polygraph is the guilty knowledge test (GKT) (Bashore & Rapp, 1993). This test operates under the assumption that a guilty individual will know more about a crime than an innocent individual would. It is therefore more desirable than other methods of questioning in that the test is designed to identify guilt as is expressed in a cognitive process not as is expressed in an emotional reaction. It is Detecting Guilty Knowledge 4 however, like the traditional methods of questioning, still rooted in the use of autonomic measures and therefore false positives and countermeasures are still of concern. This study develops a new individual classification system of guilty knowledge that is not reliant on changes in autonomic arousal but instead on event-related potentials (ERPs). This change in method thereby improves the accuracy of attempts to detect guilty knowledge because ERPs do not allow the use of countermeasures and therefore, should not subtend as many false positives as the polygraph does (Boaz et al., 1991). Using ERPs to assess credibility is also effective because, like the guilty knowledge test, this method is sensitive to cognitive events (Boaz et al., 1991). ERPs are visually represented as a series of fluctuations in electroencephalogram (EEG) recordings. These fluctuations appear as peaks and troughs in response to the presentation of stimuli in any sensory modality. The resulting ERPs are time-locked to the stimuli that are presented and are therefore used to determine the time course of cortical-level processes. By analyzing the direction of activity (positive or negative), the amplitude and latency of the wave it is theoretically possible to isolate the actual neuroelectric brain response to any certain type of stimuli. ERPs have been used in a variety of capacities and of the numerous ERP components that have been studied; the P300 and N400 have received the most attention when considering their usefulness in detecting guilty knowledge. The P300 is characterized as a positive-going neural component that occurs approximately 300 ms following the onset of a rare stimulus. This ERP component has been studied by employing the oddball paradigm in which both rare and standard stimuli are presented to the subject. In this paradigm, the P300 is elicited by the rare and meaningful stimuli. When using this paradigm as a means of detecting deception, the rare stimuli are often key aspects of a crime that Detecting Guilty Knowledge 5 would hold some meaning for a subject who was guilty (Rosenfeld, Cantwell, Nasman, Wojdac, Ivanov & Mazzeri, 1988). As is evidenced by Farwell and Donchin (1991), this method of detecting deception is somewhat effective. In their study, 20 subjects were required to take part in one of two mock crimes and their knowledge of those scenarios was subsequently tested (Farwell & Donchin, 1991). In testing, only a few of the stimuli were designed to elicit a P300 while the others were irrelevant. In this study, whenever it was possible to make a determination of whether the subject has knowledge of their own scenario, the determination was accurate; no false positives or negatives were made. In response to these results, it can be assumed that the majority of those who commit a crime will exhibit a P300 if presented with meaningful, yet rare stimuli that remind them of the crime that was committed. Conversely, those who did not commit a crime and did not have any knowledge of the crime would not exhibit a P300 to the crime relevant stimuli. As a result of further study, Johnson and Rosenfeld (1992) concluded that this method of detecting guilty knowledge is an effective way of determining whether a subject has knowledge of a crime or not. Although this method of detecting deception appears promising, it is heavily reliant on a subject’s ability to distinguish between the rare and standard stimuli that are presented. Thus, the N400 component of ERPs has also been subjected to study. The N400 is characterized by a negative-going neural component that occurs approximately 400 ms after the onset of the stimulus. Kutas and Hillyard (1980) initially discovered this component when asking participants to read a series of sentences that appeared word-by-word. Some of these sentences ending in a physically deviant way while others ended in a semantically deviant fashion. Kutas and Hillyard (1980) found that sentences that were terminated in a physically deviant way were characterized by a P300 while those that ended in a semantically inappropriate way were characterized by negativity, Detecting Guilty Knowledge 6 approximately 400 ms after the semantically deviant terminal word. Kutas and Hillyard (1980) subsequently termed this ERP component a N400 and continued to study why and how this component is elicited. Further studies conducted by Kutas, Neville and Holcomb (1987) revealed that while semantic deviations elicit the largest N400 brain potentials in amplitude, they are not the only condition that will elicit the wave. Meaningful sentences were also found to produce the N400 to the extent that they are terminated in an unexpected way. The amplitude of the N400 was actually found to be an inverse function of how strongly a person holds an expectation for the terminal word of a sentence and how strongly that expectation is violated (Kutas & Hillyard, 1984; Boaz et al., 1991). Furthermore, the N400 is only elicited in response to anomalies in linguistic information (Kutas and Hillyard, 1984). The exhibition of a N400 component has also been closely associated with the truth-value of a sentence. A study conducted by Fischler, Bloom, Childers, Roucos and Perry (1983) suggested that a N400 is elicited by words that complete a sentence in a false fashion (A squirrel is a car) and is not found when a sentence is terminated in a truthful way (A squirrel is an animal). Therefore, it is purported by Boaz et al. (1991) that if a subject has knowledge of a crime and this knowledge is tested with sentences that are terminated with either true or false endings, the subject with guilty knowledge will exhibit a N400 to those sentences that end in a false fashion. Conversely, if a subject does not have any prior knowledge about the crime, they will not exhibit a N400 to any of the sentences, no matter how they are terminated. This is because the subject will have no reason to believe that any of the sentences were incorrect. Boaz et al. (1991) tested this hypothesis by requiring participants to watch a video of either a burglary or a depiction of city-life in New York. All participants were given incentive to try to Detecting Guilty Knowledge 7 beat a lie detection test that was subsequently administered. As part of the lie detection test, participants were presented with sentences that pertained to the burglary video. These sentences ended in either a true or false fashion. The researchers expected that sentences that were terminated in a false fashion would only elicit a N400 in those that saw the video about the burglary and that those that saw the video about New York would not show an N400 to any of the stimuli. This study resulted in a correct classification of approximately 70% of the participants. Meaning that, 70% of the participants were correctly classified as having watched the burglary video or the vide