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A mock crime experiment was designed in which 100 participants were randomly assigned to five conditions: four experimental conditions in a 2 × 2 factorial design (two guilt conditions—guilty or informed innocents, crossed with two incentive level conditions—with or without a promised reward for proving innocence), and one control condition of uninformed innocents. Along with the common dependent polygraph measures, attitudes towards cooperating with the test were assessed. Results indicated that the informed innocents preferred to cooperate whereas guilty participants preferred to try and obstruct the test. These tendencies were amplified among participants who were promised a reward. The cooperative choice attenuated electrodermal responses to the critical items. Respiration measures were sensitive to the incentive level manipulation. Implications of the results for future research and for actual detection of information tests were discussed.
Criminal justice experts are eager to know whether a given person is withholding information regarding a criminal event. Therefore, scientists and forensic experts are in a continuous search for appropriate approaches and methods that can help the legal system in this respect. A psychophysiological detection of information method that serves this purpose was proposed by Lykken (1959) and since then has gained considerable scientific attention (see Ben-Shakhar & Elaad, 2003, for a review). The method is known as the Concealed Information Test (CIT), or the Guilty Knowledge Test (GKT). The CIT utilizes a series of multiple-choice questions, each having one critical or correct alternative pertaining to a feature of the crime under investigation, and several incorrect alternatives serving as controls. The critical and control items are chosen so that an innocent suspect who has no crime-related knowledge cannot discriminate among them (Lykken, 1998). Typically, if the suspect's physiological responses to the correct alternatives are consistently larger than to the controls, possession of concealed information about the event in question is inferred. This is the classic cognitive approach to the CIT (Lykken, 1974).
Research on the CIT in laboratory settings has revealed highly accurate decisions for both guilty and innocent participants (Ben-Shakhar & Elaad, 2003). However, in most of these studies, detection rates were computed for fully informed guilty participants and for fully ignorant innocents. From a practical point of view, such comparisons may raise questions. For example, innocent examinees may gain access to critical information through the mass media description of the crime. In addition, suspects could be exposed to critical information during the interrogation itself. For example, Krapohl (2011) cited a case study where an innocent suspect whom the police wanted to fail the CIT was placed in a jail cell with an agent who implanted the critical information of the investigated crime in the innocent suspect by repeating an invented story in which the critical items appeared. Critical information may also leak through contact with witnesses and other people who may have some knowledge of the crime. However, as long as innocent suspects can explain how they became aware of the critical information, the problem is not severe. But, innocent suspects who were exposed to critical details of information are frequently unaware of this exposure and are unable to account for the sources of their knowledge. Furthermore, some knowledgeable, but innocent, suspects might refuse to admit their knowledge because they might fear reprisal by the culprit.
Studying informed innocent participants is also important from a theoretical perspective. Ben-Shakhar and Elaad (2003) reported that highly motivated deceptive guilty participants were more often detected in the CIT than less motivated deceptive guilty participants. It seems that whenever motivation to prove innocence is involved, informed guilty participants are encouraged to invest more effort to obstruct the test and avoid detection (motivation to cope with the test) while ignorant innocent participants are not affected by the motivation manipulation at all. Therefore, whenever guilty and innocent participants are compared when accounting for factors other than mere knowledge (e.g., emotions, act of deception, motivation to prove innocence), one should consider informed innocents in addition to ignorant innocents.
Results of mock-crime studies where innocent participants were exposed to critical information in an innocent context (e.g., Ben-Shakhar, Gronau, & Elaad, 1999; Bradley & Rettinger, 1992; Bradley & Warfield, 1984) showed that the detection rates of guilty participants were higher than those of innocent participants who shared the same critical information (but see also Gamer, Kosiol, & Vossel, 2010; Nahari & Ben-Shakhar, 2011, for different reports). The following question is whether informed innocents can be discriminated from noninformed innocents. Elaad and Ben-Shakhar (1989) reanalyzed Bradley and Warfield's (1984) data and demonstrated that the mean detection score based on the pooled data of all three informed innocent groups tested in this study was greater than chance. Similar results were reported by Ben-Shakhar et al. (1999) and more recently by Zvi, Nachson, and Elaad, (2012) and by Elaad (2013). To conclude, the mere knowledge of the relevant information in itself enhances physiological responses of informed innocent examinees.
In all these studies, the Guilty Action Test (GAT) questioning format (Bradley & Warfield, 1984) was used. The GAT format changed the question wording from passive knowledge (e.g., “What was the color of the stolen envelope?”) to active participation (e.g., “Was the color of the envelope you stole …?”). This guarantees that informed innocents are truthful when denying involvement with the crime-related items whereas guilty participants' denials are lies. However, when both deception and knowledge were controlled, and the effect of guilt was examined alone, using the standard CIT (“Do you know …?”) format, very high rates of false positives (90% and 70%) were reported for informed innocent participants (Bradley, MacLaren, & Carle, 1996). Results suggested that, when informed innocent examinees were put into a situation where they deny information they know is true (as is the case with the CIT), they are especially reactive on the critical items. When informed innocent participants were truthful on the GAT, 50% were still judged as guilty. This rate is higher than typically found with innocent participants who have no knowledge. It seems that, in experimental settings, guilt alone is insufficient to differentiate between informed guilty and informed innocent participants (Elaad, 2009, 2011).
Hartwig, Granhag, and Stromwall (2007) found that a majority of guilty participants in a mock study reported to have a plan before facing the interrogation whereas only a few innocent participants reported to having prepared for the interview. Innocent suspects' behavior was explained by their belief that telling the truth “as it is” is sufficient to exonerate them. Applying these results to real-life interrogations may suggest that guilty suspects are threatened by the police polygraph test because they know that their odds of “beating” the test are low. Actually, they expect to be punished after the completion of the test. Those who ultimately agree to take the test despite the poor odds have some hope of success based on rumors and popular literature indicating that the polygraph makes mistakes. Such guilty suspects understand that their interest (to hide the truth) conflicts with the polygraph examiners' interest (to reveal the truth) and in order to succeed they have to obstruct the polygraph operation. They mistakenly believe that this can be achieved by increased attention to the critical items. However, attention enhances physiological responding to the identified information.
Innocent suspects who agree to take the test expect to be released from further questioning after its completion. They feel confident that they are able to prove their innocence in the test and that the polygraph operators' interest (to arrive at a correct decision) coincides with their own interests (to be found truthful). Furthermore, innocent suspects tend to have a naïve faith in the power of their own innocence to set them free, and seem to trust the criminal justice system (Kassin, 2005).
This attitude of innocent suspects was observed in earlier accounts on guilty and innocent people's verbal behavior that showed that liars and truth tellers have different strategies in response to the interrogation (e.g., Colwell, Hiscock-Anisman, Memon, Woods, & Michlik, 2006; Granhag & Hartwig, 2008). Specifically, the psychology of guilt predicts that guilty suspects will use uncooperative strategies with respect to possibly self-incriminating information (Stromwall, Hartwig, & Granhag, 2006), whereas innocent suspects will use much more straightforward strategies (Kassin, 2005). For example, innocent people may volunteer being at the crime scene, while guilty people tend to avoid mentioning such information (Hartwig, Granhag, Stromwall, & Vrij, 2005). Overall there is support for the notion that truth tellers are more cooperative and forthcoming than liars (DePaulo et al., 2003).
Cooperation instructions were previously included in an altered polygraph Comparison Question Test (Bradley, MacLaren, & Black, 1996; Cullen & Bradley, 2004). It was reported that, although informed innocent participants recognized the relevant questions as threatening, their cooperation (truthful answers to the relevant questions) was associated with lower physiological responses than those of the less cooperative guilty participants.
The two different states of mind (that of guilty examinees and that of innocents) were the focus of Zvi et al.'s (2012) study. Zvi and colleagues instructed guilty and informed innocent participants to either cope (exert effort to avoid detection) with the polygraph or be cooperative. Results indicated that guilt was associated with stronger physiological responses to the critical items than informed innocence and that coping instructions were associated with stronger physiological responses to the critical items than cooperative instructions. Note that Zvi et al. (2012) used the GAT questioning format and therefore compared deceptive guilty participants with truthful informed innocents. In another recent study, Elaad (2013) used only informed innocent participants in the GAT format and showed that cooperation instructions, supported by incentive to cooperate, attenuated the responses to identified critical details.
Both Zvi et al. (2012) and Elaad (2013) reported that informed innocent participants who were motivated to pass the test could have deeply encoded crime-related memories but still attenuate their responses to the critical items during the GAT. This stands in contrast to the results of other recent studies that reported no different responses to the critical items between informed innocents and guilty participants (Gamer, 2010; Gamer et al., 2010; Nahari & Ben-Shakhar, 2011). Gamer et al., (2010) concluded that, when informed innocents are able to remember critical details of the crime during the GAT, they have a high risk of failing the test. These contrasting results need more research, and the present study will provide further answers to the deeply encoded information question.
Most important, the participants in both previous studies (Elaad, 2013; Zvi et al., 2012) were not free to decide for themselves whether they were willing to cope or cooperate on the test. It may be argued that such a procedure lacks ecological validity. The present study seeks to examine whether guilty and informed innocent participants demonstrate different levels of willingness to cooperate on the test when they are informed of the advantages that cooperation has for innocent but not for guilty examinees. Results should shed light on the potential benefits of incorporating cooperation instructions in real-life detection of information test settings. It is suggested that a proper warning that cooperation is beneficial to the interests of innocent examinees and operates against the basic interests of deceptive participants encourages innocent but not guilty participants to adopt a cooperative attitude toward the test, and behave accordingly.
Unfortunately, guilt and innocence in low-stakes experimental settings fail to simulate real guilt and real innocence. Participants in an experiment know perfectly well that they are participating in a simulation and that no harm will be inflicted upon them as a consequence of the polygraph test results. One way to compensate for this shortcoming is to manipulate the level of motivation to prove innocence, on the assumption that higher motivation levels simulate better than lower motivation levels in actual testing conditions. The present study will therefore manipulate the participants' motivation to prove their innocence. Hence, the option to either cooperate or not on the test will be presented to motivated and less motivated guilty and informed innocent participants tested with the GAT questioning format. It is hypothesized that results will show a clear preference of informed innocents to cooperate. In contrast, guilty examinees will prefer to cope. From a theoretical point of view, results may provide further support for the distinctive state of mind that guilty and informed innocent examinees possess.
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The purpose of the current study was to further explore the different states of mind of guilty and informed innocent examinees undergoing detection of information tests. These states of mind trigger different responses to cooperative instructions from guilty and innocent examinees. Two earlier studies already examined this matter (Elaad, 2013; Zvi et al., 2012). Zvi et al. (2012) manipulated the guilt of the examinees (guilty or informed innocent) and the instructions they received (to cope or to cooperate on the test), and controlled the incentive level (all participants were promised a reward for success). Elaad (2013) manipulated the instructions (whether or not cooperating instructions were delivered) and the incentive level (with and without an external reward for success), where guilt was controlled (only informed innocent participants were examined). The present study manipulated guilt and incentive level while controlling the instructions to cooperate. Specifically, the present study offered both guilty and informed innocents two options, to cope or to cooperate, enabling them to make their own choice which strategy to adopt.
The present cooperating ratings show that guilty participants were less inclined to cooperate on the test than informed innocents who tended to be quite cooperative. The cooperation tendency was enhanced when a reward for successful outcomes was promised. It was further determined that choosing to cooperate predicts attenuated SCR responses to the critical items. Furthermore, although not significant, cooperation reports predicted the tendency to reduce FPWL and RLL responses as well.
A rather speculative explanation for the association between the willingness to cooperate and attenuated SCRs rests on the point that SCRs are affected by whether a probe in the CIT comprises a central or a peripheral aspect of the respective crime (e.g., Gamer & Berti, 2012). Thus, for participants in a coping state of mind, the critical items may become “central” whereas for those in a cooperative state of mind the critical item may become peripheral. Future research is encouraged to further examine and develop this idea.
Overall, guilt or innocence and the incentive levels were not associated with recall of crime-related items. This enables a better comparison between the various experimental conditions without a possible recall artifact.
Results showed that sheer possession of concealed information contributed to enhanced responses to the critical items when compared with uninformed participants. Cooperation attenuated SCRs and to some extent also FPWL responses to the critical items of informed innocents. On the other hand, RLL was the only measure that was sensitive to the incentive level manipulation. ROC analysis further supported these results. SCR was the most effective measure in detecting the critical information and the most sensitive measure to the guilt manipulation. These results are of no surprise as the distinctive sensitivity to critical information of electrodermal responses in general (e.g., Bradley, Malik, & Cullen, 2011), and SCR in particular (e.g., Cutrow, Parks, Lucas, & Thomas, 1972; Verschuere et al., 2007), are well documented in the literature of CIT and GAT questioning formats.
SCR provided a clear distinction between high-incentive guilty participants, who reacted to the critical information much more than either high-incentive or low-incentive innocents. These results are straightforward but important. They suggest that providing cooperating instructions and clear guidance on how to implement such cooperation may enhance correct classification of guilty and innocent examinees in the GAT.
The present results support those of Zvi et al. (2012) who reported that both innocence and cooperating instructions attenuated SCR responses to the critical items. Specifically, the informed innocent participants were less responsive to the critical items than the guilty examinees, and when the participants were instructed to cooperate on the test, SCR responses decreased as well. Results also coincide with those of Elaad (2013). Elaad examined the association between a promised reward for either success in proving innocence (goal-oriented instructions) or success in being cooperative (task-oriented instructions) and the willingness of informed innocent examinees to adopt the goal- or task-oriented attitude. He showed that high-incentive cooperation instructions attenuated informed innocents' responses to the critical items.
The fact that high-incentive informed innocent participants were more inclined to cooperate on the test than the low-incentive informed innocents may suggest that in real life, where stakes are higher (Verschuere, Meijer, & De Clercq, 2011), and where motivation to prove innocence is much stronger, the tendency of innocent examinees to cooperate may be further enhanced. The reverse effect may be true for guilty examinees. Although not significant, high-incentive guilty participants were less inclined than their low-incentive counterparts to cooperate on the test. As a result, their physiological responses to the critical items were enhanced.
The present results may provide further support for previous suggestions (e.g., Zvi et al., 2012) to advise examinees in real life to cooperate on the test and guide them how to do so. A proper warning should be followed that cooperation serves the interests of innocent examinees and operates against the basic interests of guilty examinees. This may encourage innocents to adopt a cooperative attitude and behave accordingly. They are expected to calm down and try to assist the polygraph examiner reach the expected (correct) decision. Such cooperation instructions would convince guilty examinees to avoid cooperation, adopt a coping attitude, and double their efforts to obstruct the test.
Limitations of the Present Study
The present study entails a laboratory experiment where stakes are low and participants were well aware that no harm would be inflicted upon them as a result of their performance on the test. Specifically, the threat is not the same as the threats that criminal suspects usually experience during actual testing. To compensate for this shortcoming, we manipulated two incentive levels to prove innocence with the expectation that the higher incentive level will simulate better than the lower incentive level real-life conditions. Still, the higher incentive level does not simulate real-life testing. This dictates caution when applying the present results to actual testing.
The present sample of participants consisted of undergraduate students enrolled in a psychology course who participated in the study for course credit. One argument against using psychology students is the possible resentment they may feel toward the requirement to participate in a departmental study. However, in actual testing, innocent suspects may often manifest resentment when they are asked to take a polygraph test.
The present sample is largely a female sample. Although females were no more or less inclined than males to either cope or cooperate on the test, caution is still recommended when generalizing the results to largely male suspects.
To sum up, the present study extends previous accounts on the distinctive motivational processes or states of mind of informed innocent and guilty examinees to polygraph tests in general and to detection of information tests in particular. It has demonstrated that innocent examinees prefer to cooperate on the test whereas guilty examinees prefer not to cooperate. These distinctive states of mind add another theoretical and practical level to the cognitive approach that emphasized the recognition of the critical information in detection of information tests. This addition is important because the cognitive rationale fails to explain why informed innocent examinees respond less to critical items than informed guilty examinees. The present motivational approach deserves more research attention than is currently provided.