On September 21st in 2001, Lofti Raissi was the first person to be arrested for the 9/11 attacks. He was under suspicion of training pilots who flew an aircraft into the Pentagon. In prison, Raissi became known as the “Bin Man”, named after Osama bin Laden, and was stabbed twice. After five months in prison, the court concluded Raissi had no association with the attacks and had been wrongfully convicted.
Especially in high impact situations such as terrorist attacks, detection of those responsible is of the utmost importance. Still, research found that people are generally not very good at distinguishing between truthful and deceptive statements of suspects and witnesses (Granhag, Andersson, Stromwall, & Hartwig, 2004). Multiple studies have shown that the accuracy rates fall below 60% (Kraut, 1980; Vrij, 2000). Even police officers have failed to detect deception better than chance (Hartwig, Granhag, Stomwall, & Vrij, 2004). So, the ability of people as lie-detectors is weak. Therefore, the forensic field has been started to actively develop new physiological response measurements for detection of deception, including those based on eye-tracking technology (Kovaled, Luniakova, & Menshikove, 2016). The current study will aims to examine eye-tracking technology as a new physiological response measurement for the detection of deception.
Specifically, eye-tracking technology will be researched as potential technique to conduct a new version of the Concealed Information Test (CIT) for the forensic practice. The purpose of the CIT is to detect the presence of guilty knowledge by means of physiological measurements. A recent study by Derrick, Moffit, and Nunamaker (2011) suggests that eye-tracking technology can be a very efficient measurement for the CIT, which is also referred to as the Guilty Knowledge Test (GKT; Lykken 1959). In their pilot study, they discussed eye-tracking technology as means to determine if an individual has guilty knowledge of a prohibited improvised explosive device (IED). They discriminated between two groups: participants familiar with the IED and participants unfamiliar with the IED. As a result, the eye behaviour based CIT yielded 100% accuracy in discriminating between those that had to build the IED and those that had not.
Although the results of this pilot study are promising, only 11 participants were part of the sample size used. On the whole, this seems to be a sufficient reason for further research into eye-tracking technology for discrimination between the guilty and the innocent. The current research will therefore build upon the study by Derrick, MOffit and Nunamaker (2011). First, the following questions will be addressed: What is the CIT and how accurate is this method? How can eye-tracking technology be used as a measurement for the CIT? And how will the present study eventually perform a CIT using eye-tracking technology?
1.1 Concealed Information Test
The use of physiological measures to detect deception, also known as psychophysiological detection of deception (PDD), have a long history in psychological science (Lombroso, 1895). PDD methods measure physiological changes e.g. facial expression, voice frequency, heart rate, breathing patterns, skin conductance, and changes within the brain (Andreassi, 2000). One PDD method that is often found to discriminate between the guilty and the innocent is the Guilty Knowledge Test (GKT; Lykken 1959). It is nowadays commonly referred to as the Concealed Information Test (CIT; Verschuere, Ben-Shakhar, & Meijer, 2011). The CIT utilizes multiple-choice questions using information that is presumably known only to the criminal. The following case will give a preview of a crime that can be properly used in an interrogation with a CIT.
For a prototypical CIT, a series of questions is prepared, which pertains various aspects of the crime presented above. The following will give some example questions.
The questions all have one relevant item (e.g. a feature of the crime under investigation) and several neutral (control) items. The neutral items are chosen so that innocent suspects would not be able to discriminate them from the relevant one (Lykken, 1998). Usually, suspects are instructed to say “no” to all possibilities. It assumes that suspects aware of crime-relevant information, will be physiologically more reactive to items related to the crime than to the similar but crime-irrelevant items (Bradley & Rettinger, 1992). If information about the event has not leaked out, the chance that innocent suspects would consistently show more physical responses to the relevant than to the neutral alternatives depends only on the number of questions and the number of alternative answers per question. So, the rate of false-positive misqualifications can be controlled such that maximal protection for the innocent is provided.
Lykken (1974) also referred to this process as orienting reflex: “… for the guilty subject only, the ‘correct’ alternative will have a special significance…which will tend to produce a stronger orienting reflex than that subject will show to other alternatives (p. 728)”. The orienting reflex (OR) is elicited by novel and/or significant stimuli (Sokolov, 1963). The organism orients to these potentially important stimuli in order to analyze them more thoroughly and to prepare for appropriate responding. Indeed, for the guilty only, the correct items are of special significance and will grasp attention. The orienting reflex is associated with a specific pattern of physiological responding – increase in skin conductance, heart rate deceleration, respiratory suppression (Lynn, 1966). Furthermore, recent research suggested that eye behaviour can also be added to that list (Derrick, Moffitt, & Nunamaker, 2011).
1.2 Eye-tracking technology as potential measurement for the CIT.
A prerequisite for a successful CIT is memory for crime details. Research found that eye gaze behaviour when viewing familiar images differ from unfamiliar images. These differences include less frequent fixations in fewer regions and more randomness in eye movement patterns (Althoff & Cohen, 1999). Schwedes and Wenturn (2016) examined eye movement, mainly eye fixation, and memory effects. They found an increased duration of fixations to known relative to unfamiliar stimuli. This effect even occurred when knowledge of the stimulus was deliberately concealed.
In addition, recent findings support the use of eye movements as markers of memory during concealed recognition but also suggest caution when familiarity is only a consequence of one brief exposure (Millen, Hope, Hillstrom, & Vrij, 2017). Overall, eye movement (i.e. eye fixation and eye gaze behaviour) are found sufficient responses for memory assessment. Because of these findings, eye-tracking technology can be used to conduct a version of the CIT. Both eye fixation and eye gaze behaviour are proven to be used as accurate variables.
1.3 Accuracy CIT and eye behaviour
Multiple studies have reported high accuracy rates for differentiating guilty from innocent suspects using CIT. For example, Ben-Shakhar and Furedy (1990) showed in their meta-analysis of 10 CIT laboratory experiments that 84% of the participants with concealed knowledge and 94% of those without were correctly classified. A more recent research showed similar results with successful detection of 76% of the guilty examinees and slightly lower detection, 83%, of the innocent ones (MacLaren, 2001). Elaad (1990) and Elaad, Ginton and Jungman (1992) have showed in their field studies equally high detection of innocent suspects (98% and 94%, respectively), but somewhat lower detection accuracy among guilty suspects (42% and 76%, respectively).