Cognitive load interview protocols are designed to make interviews more demanding for suspects. This increased demand has a greater effect on liars than on truth tellers because liars already find being interviewed more mentally taxing than do truth tellers. The result is that cognitive load interview protocols facilitate discrimination between liars and truth tellers.
Lying in an interview setting is often more cognitively demanding than truth telling. First, formulating the lie itself is cognitively taxing. Liars need to make up their stories while monitoring their fabrications so that they are plausible and adhere to everything the observer knows or might find out. In addition, liars must remember their earlier statements and know what they told to whom, so that they appear consistent when retelling their story. Liars should also avoid making slips of the tongue and should refrain from providing new leads to investigators. Second, liars are typically less likely than truth tellers to take their own credibility for granted, in part because truth tellers typically assume that their innocence will shine through. As such, liars will be more inclined than truth tellers to be conscious of, and hence monitor and control, their demeanor so that they will appear honest to the lie detector. Monitoring and controlling one’s own demeanor are cognitively demanding. Third, because liars do not take their credibility for granted, they may monitor the interviewer’s reactions more carefully to assess whether they are getting away with their lie. Carefully monitoring the interviewer also requires cognitive resources. Fourth, liars may be preoccupied with the task of reminding themselves to act and role-play, which requires extra cognitive effort. Fifth, liars have to suppress the truth while they are lying, and this is also cognitively demanding. Finally, whereas activating the truth often happens automatically, activating a lie is more intentional and deliberate and thus requires mental effort.
Many sources support the premise that lying is cognitively demanding. First, in police interviews with real-life suspects, lies are accompanied by increased pauses, decreased blinking, and decreased hand/finger movements, all of which are signs of cognitive load. Second, police officers who saw videotapes of suspect interviews reported that the suspects appeared to be thinking harder when they lied than when they told the truth. Third, participants in mock-suspect experiments directly assessed their own cognitive load during interviews and reported that lying is more cognitively demanding than truth telling. Finally, deceiving is associated with activating executive, “higher” brain centers (such as the prefrontal cortex), which are typically activated when high cognitive load is experienced.
By using protocols that introduce additional cognitive load, investigators can exploit liars’ higher cognitive demand to facilitate discrimination between liars and truth tellers. For example, interviewees could be asked to recall their stories in reverse order. This task is cognitively more demanding than recalling a story in chronological order. Liars, whose cognitive resources are depleted by the more demanding act of lying, find reverse order recall more debilitating than do truth tellers because liars have fewer cognitive resources left over than truth tellers. Indeed, research has demonstrated that liars and truth tellers differ more from each other in terms of displaying signs of cognitive load when they recall their stories in reverse order than in chronological order. The occurrence of more noticeable differences between liars and truth tellers should facilitate lie detection. Indeed, investigators were more accurate in discriminating between liars and truth tellers when the interviewees told their stories in reverse order than in chronological order.
An alternative technique to induce additional cognitive load is to require interviewees to perform a concurrent secondary task (time-sharing) while being interviewed. Again, liars, whose cognitive resources are already partially depleted by the act of lying, find this additional, concurrent task particularly debilitating. An experiment revealed that this showed up as poorer performance on the primary task (e.g., providing a statement during the interview) and also on the secondary task (e.g., determining whether each figure presented on a screen was similar to the target figure presented earlier).
Investigators sometimes have evidence available, such as fingerprints and closed-circuit TV footage, that may link a suspect to a crime. They can then present this incriminating evidence against a suspect in a strategic fashion to increase cognitive load by limiting the number of acceptable explanations suspects can offer to account for the current situation. Suppose that the suspect’s car was noticed near the crime scene just after the crime had taken place but that the suspect did not refer to the car in his or her alibi. After being confronted with this piece of evidence, the suspect may reply that he or she had simply failed to mention previously that he or she had used the car on that particular day, thereby adapting his or her story to match the evidence. However, suppose that the police officer does not reveal at this stage that the car was noticed near the crime scene but asks some questions about the car instead (e.g., “Did you use your car that day?”). When confronted with the evidence after these questions, the suspect has fewer opportunities to provide acceptable solutions if he or she has already told the interviewer that he or she did not use the car on that particular day. The number of acceptable solutions would be reduced even further if the suspect indicated that he or she did not lend the car to anyone else and that nobody else had the car keys.
In sum, investigators using cognitively based interview protocols increase their ability to discriminate between liars and truth tellers by making the interview situation more taxing for interviewees.
- Hartwig, M., Granhag, P. A., Stromwall, L., & Kronkvist, O. (2006). Strategic use of evidence during police interrogations: When training to detect deception works. Law and Human Behavior.
- Vrij, A., Fisher, R., Mann, S., & Leal, S. (2006). Detecting deception by manipulating cognitive load. Trends in Cognitive Sciences, 10, 141-142.
- Vrij, A., Fisher, R., Mann, S., & Leal, S. (in press). Increasing cognitive load in interviews to detect deceit [Invited chapter]. In B. Milne, S. Savage, & T. Williamson (Ed.), International developments in investigative interviewing.
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