Using Forensic Psychology to Teach Basic Psychological Processes

Abstract

Teachers can incorporate topics in forensic psychology into lower level courses to increase student interest and to show how psychological processes influence outcomes in high-stakes applied contexts. One such topic is eyewitness identification, which teachers can use to show how stress affects memory and how memories can become distorted during encoding, storage, retrieval, and even postretrieval. A second topic is lie detection, which teachers can use to illustrate the limits of our ability to interpret the nonverbal behavior of others. Lie detection also illustrates the use and misuse of physiological measures (polygraph, functional magnetic resonance imaging, electroencephalogram) as indicators of psychological states. Like memory errors by eyewitnesses, the limitations of lie detection can lead to innocent people being accused and convicted of crimes they did not commit.

Keywords

forensic psychology introductory psychology eyewitness identification lie detection

Attention, memory, influence, nonverbal communication, physiological arousal, measurement. These basic psychological processes are covered in every introductory psychology course. These processes are also fundamental elements of the legal system. By highlighting the links between psychology and the legal system, teachers can engage student interest and promote understanding of basic psychological phenomena. Virtually all college students have seen movies and television shows depicting crime and the legal system. Some students have even been witnesses to, victims of, or even perpetrators of crimes. Examples from the field of forensic psychology can serve as entry points for student understanding of basic psychological principles. Concepts that may initially seem abstract or distant from a student’s personal experience become more accessible when explained via their relation to the legal system. Forensic psychology—the use of psychological theories, methods, or research findings to advise, evaluate, or reform the legal system—provides many examples of the practical uses of psychological science (Costanzo & Krauss, 2012). This article will briefly summarize research in two areas of psychology and law—eyewitness identification and lie detection—to illustrate the ways in which psychological processes are at the core of our legal system.

Eyewitness Identification

Eyewitness identification is one of the most heavily researched topics in the field of psychology and law. It is also one of the most important. Nearly 300 people have been convicted of crimes but later proven innocent using DNA evidence. Research on these cases has revealed that mistaken eyewitness identification is the leading cause of wrongful convictions. In 76% of criminal cases where the wrong person was convicted, one or more eyewitnesses had erroneously identified the defendant (www.innocenceproject.org). This consequential source of error in the legal system can be traced to errors in attention, memory, and social influence. One prominent perspective in psychology conceptualizes memory as having three components: encoding, storage, and retrieval (Atkinson & Shiffrin, 1969; Foster, 2008). Crucially, this means that eyewitness memory errors can enter at each stage in the process.

Eyewitnesses must first encode sufficient and accurate information about the criminal. As any good defense lawyer will point out during trial, several physical factors can impair an eyewitness’s ability to encode information about an apparent perpetrator. These factors include the level of ambient light at the time of the crime (to which a lawyer might ask, “Was it dark or turning dark when the man was robbed on the street?”), the eyesight of the witness (Was she wearing her eyeglasses at the time of the crime?), and the distance between the witness and the criminal (Was she standing too far away to get a clear look at the robber’s face?). Although such factors are important to consider, research indicates that psychological factors also have a dramatic effect on one’s ability to encode information about a criminal.

Mark A. Costanzo.

One psychological factor that interferes with encoding is stress. Eyewitnesses to crimes commonly experience psychological stress and fear of personal harm. These psychological states narrow attention and damage the process of encoding. For example, in a series of dramatic studies, Morgan and his colleagues (2004) examined eyewitness memory in more than 500 soldiers who underwent “survival training.” This realistic training involved capture by enemy forces and either a low- or high-stress interrogation in a simulated prisoner-of-war camp. Interrogations lasted about 40 min, and the high-stress interrogations included actual physical abuse. Here, as in other studies, stress impaired encoding. When Morgan et al. later asked the soldiers to identify their interrogators in photographic or live lineups, soldiers in the low-stress condition were able to identify their interrogators accurately about 71% of the time; those in the high-stress condition had an accuracy rate of 38%. In addition, only 25% of the soldiers in the low-stress condition identified the wrong person, whereas 58% of the soldiers in the high-stress condition identified the wrong person. These findings are consistent with findings from other studies. For example, several researchers have found a “weapons focus effect” whereby eyewitnesses who see a perpetrator holding a gun or knife are less able to identify the perpetrator in a lineup. Fear for their own safety apparently causes these eyewitnesses to focus their attention on the weapon instead of the physical characteristics of the criminal holding the weapon (Pickel, Ross, & Truelove, 2006). Finally, a meta-analysis of 27 studies found that high stress substantially disrupts the encoding process and consequently reduces the rate of accurate identifications (Deffenbacher, Bornstein, & Penrod, 2006).

Once encoded, memories must be stored in the brain for recall at a later time. Although scientists do not fully understand how a memory is biochemically stored in the brain, they do know that memories appear to deteriorate over time. Memories also appear to be become increasingly susceptible to distortion and corruption as time goes by (Flin, Boone, Knox, & Bull, 1992; Schacter, 2001). For eyewitnesses, there can be delays of days or weeks between the time they witness a crime and the time investigators ask them to identify the likely perpetrator.

Even if the memory stored is accurate, distortion and error can occur at retrieval. Typically, this occurs because of biased or suggestive questioning or biased lineups. In a classic series of studies, Loftus and Palmer (1974) demonstrated the surprising power of suggestive wording to alter recall of an event. Several groups of participants viewed the same video of a car crash. After a 1-week delay, Loftus and Palmer asked each group slightly different questions about what they had seen. For example, some participants were asked, “How fast were the cars going when they contacted each other?” Others were asked, “How fast were the cars going when they smashed into each other?” This small change in wording led the first group to estimate the speed at 31 miles per hour, whereas the second group estimated the speed at 41 miles per hour. Similarly, participants who were asked, “Did you see the broken headlight?” were more than twice as likely to remember seeing a broken headlight than were participants who were asked, “Did you see a broken headlight?”

The influence of suggestive comments on eyewitness identification extends beyond the act of retrieval. A “post-identification feedback effect” has been demonstrated across many studies (Douglass & Steblay, 2006). This effect refers to distortions in memory and confidence that an investigator’s feedback can produce after an eyewitness has identified a suspect. Sometimes after an eyewitness has identified a suspect from a lineup, a police officer will provide confirming feedback such as, “Good, we thought he might be the guy who did it.” Such feedback has been shown to boost the eyewitness’s confidence in the accuracy of his or her identification. Compared to witnesses who receive no feedback, witnesses who receive confirming feedback later remember that they had a better view of the crime, that they made the identification more easily, and that they paid more attention to the crime while it was occurring (Wells & Bradfield, 1998). The increased confidence instilled by confirming feedback can have a critical impact during trial because jurors and judges view highly confident eyewitnesses as more accurate and credible (Douglass, Neuschatz, Imrich, & Wilkinson, 2010).

Research on eyewitnesses not only demonstrates how factors such as context, psychological stress, and suggestive questioning influence the functioning of human memory; it also provides teachers with an opportunity to dispel the prevalent misconception that human memory is analogous to a video recording. This research also provides a compelling illustration of the malleability of memory and supports the view that memory is constructed and reconstructed over time (Friedman, 2004). Finally, teachers can use the topic of eyewitness identification to show students how psychological research can be an effective tool for reform. Specifically, this body of research has led to changes in how investigators question eyewitnesses and how they construct lineups. Research-based reforms include bias-reducing instructions to eyewitnesses, careful construction of unbiased lineups, collecting eyewitness confidence ratings at the time of identification, video recording of identifications, sequential lineups, and the use of expert testimony at trial (for a full description of these reforms, see Costanzo & Krauss, 2012).

Lie Detection

Lie detection plays a crucial role in the legal system. During trials, the jury is assigned the role of assessing the credibility of witnesses who testify in court. Judges instruct the jurors to pay careful attention to witnesses’ “demeanor on the witness stand” and “manner of testifying” as a means of detecting whether a witness is lying or attempting to conceal information (Committee on Model Jury Instructions, 2004). Police officers also rely on lie detection. Decisions about which suspects to interrogate are sometimes based on a police officer’s suspicion that a criminal suspect is not being truthful. Indeed, what has been termed the misclassification error is an essential cause of false confessions. This error refers to misclassifying an innocent suspect as guilty and then subjecting him or her to a high-pressure interrogation that can produce a false confession (Leo & Drizin, 2010). Misclassification is often the result of misreading the verbal and nonverbal behavior of a suspect as indicative of deception. Once a suspect is in the interrogation room, the interrogator’s perception that a suspect is lying can increase the length and intensity of the interrogation.

A common claim about lie detection is that one can tell whether people are lying or telling the truth by observing their behavior. Over the past two decades, researchers have conducted hundreds of studies that generally do not support this claim. In many such studies, participants see video recordings of people lying or telling the truth and try to determine which statements are true and which statements are lies. Because there are only two possible response options, the chance rate of accuracy on such tasks is 50%. In a meta-analysis of 384 studies of human lie detection ability, overall accuracy was only modestly above chance—about 54% (Bond & DePaulo, 2006). When liars were able to plan out and rehearse their lies (as guilty suspects often do before they talk with police), detection rates dropped by about 2%. One problem is that people attempting to decode lies usually rely on the “liars stereotype,” a misguided belief that when lying, people predictably exhibit cues such as fidgeting, averting their gaze, verbal disfluency, and self-touching.

Unfortunately, many training programs teach interrogators to use verbal and nonverbal cues as indicators of deception. In studies using actual interrogation training videos, researchers have found that although training improves confidence in lie detection ability, it does not improve accuracy (Kassin & Fong, 1999; Vrij, Mann, Kristen, & Fisher, 2007). In one study, police detectives and college students watched videos of prison inmates lying and telling the truth. Although students were able to detect lies at a rate slightly above chance, the accuracy rate of detectives did not exceed chance. Detectives, however, were substantially more confident in their ratings (Kassin, Meissner, & Norwick, 2005). This combination of high confidence and low accuracy can create serious problems by generating a confirmation bias in the interrogation room (Meissner & Kassin, 2004). A police officer may initially develop a belief that a suspect is guilty based on the suspect’s “suspicious” behavior. Once the officer forms that belief, the ambiguous nonverbal behavior of the suspect (e.g., nervousness, gaze aversion, distress) may be interpreted as further evidence of deceptiveness and guilt. The interrogator may then step up the pressure on the presumably guilty suspect. Once a confirmation bias is triggered, behavior that contradicts the officer’s belief in guilt is more easily dismissed or even reinterpreted as additional evidence of guilt.

The Polygraph

If humans are unable to tell when other humans are lying, maybe machines can do better. For centuries, designers of legal systems have longed for a technological device capable of exposing lies. If an infallible lie detector is ever devised, it will revolutionize the legal system. Suspects attached to the device could answer a few direct questions (e.g., “Did you murder John Doe?”), and the answers would tell investigators all they would need to know. Although pursuing a technological solution to the problem of lie detection is a reasonable goal, no one has yet developed a reliable device.

The polygraph was developed by William M. Marston, a psychologist and lawyer who attempted to detect lies based on rises and dips in blood pressure readings. (Interestingly, Dr. Marston also created the comic book character “Wonder Woman,” who carried a “lasso of truth” that forced criminals to confess to their crimes.) Modern polygraphs measure changes in blood pressure, respiration rate, heart rate, and skin moisture. These changes are tracked and displayed as moving lines on a computer screen while the suspect is answering questions about a crime. The polygraph test is based on the simplistic theory that the act of lying creates physiological arousal. The polygraph is one aspect of a broader effort in psychology to use physiological measures to access psychological states. Research on polygraphing provides a good example of the complexities and pitfalls of inferring psychological states from imperfect physiological measures.

Until 1988, private employers used the polygraph to screen job candidates. The Polygraph Protection Act of 1988 prohibited most private employers from using the polygraph to make decisions about whom to hire or fire. There are, however, exemptions for private employers whose employees deal with national security; public employers are also exempt from the prohibition. Police departments, the Central Intelligence Agency, the Federal Bureau of Investigation, the Drug Enforcement Administration, and other law enforcement agencies routinely use the polygraph for employment screening. In the criminal justice system, polygraphs are often administered to criminal suspects during the interrogation process.

On its own, a polygraph machine merely provides measures of physiological arousal. It is only when the device is paired with a systematic questioning procedure that the polygraph becomes a lie detector. The most widely used questioning procedure is the control question test (CQT). The assumption underlying use of the CQT is that a suspect’s physiological reactions will be significantly elevated when he or she is lying. The so-called control questions are designed to make the suspect uncomfortable, but they are not directly related to the crime under investigation. For example, a suspect may answer the question, “During the first 20 years of your life, did you ever do something dishonest or illegal?” Anyone who answers “no” is assumed to be lying. Investigators compare a suspect’s reactions when answering such control questions with the suspect’s reactions to relevant questions about the specific crime being investigated. The theory behind CQT is that innocent suspects will react more strongly to the control questions, whereas guilty suspects will react more strongly to the relevant questions. A variant of the CQT uses the relevant question as its own control. So, in a murder case, a suspect would be instructed to answer the same question twice (Did you stab Joe?), once with “yes” and once with “no.” Investigators can then compare responses to the same question to see which answer produced greater arousal.

Research has revealed several weaknesses of polygraphing. One source of error arises out of individual differences in reactivity. Some guilty people are physiologically nonreactive. For them, lying does not produce a strong emotional response. Conversely, some innocent suspects react strongly to questions about whether they committed a crime. This may be especially true for innocent suspects who do not trust the polygraph and fear that they will be falsely accused. A second source of error may be attributable to the examiner—the person who sets up the polygraph and asks the questions. Unfortunately, it is impossible to fully standardize the behavior of examiners. Examiners vary in how much anxiety they elicit in suspects and in how suspicious they appear toward the suspect. There are also significant cross-examiner differences in the questions asked and the type of scoring used (Iacono, 2009). Finally, there is the problem of countermeasures—the use of self-stimulation tactics to confound the polygraph. Suspects might increase their arousal during control questions (e.g., by biting their tongue) or decrease their arousal during relevant questions (e.g., by counting backwards from 100 by increments of 7). Such countermeasures can cut the rate of accurate lie detection by half (Honts, Raskin, & Kircher, 1994).

Teaching about the polygraph also provides opportunities to introduce other important topics during class. For example, the polygraph provides an excellent example for teaching types of error using a 2 × 2 table: Criminals can either be lying or telling the truth and the polygraph can either indicate they are lying or being truthful. Under carefully controlled, but somewhat unrealistic conditions, the false positive rate (innocent suspects incorrectly classified as guilty) is about 17%, whereas the false negative rate (guilty suspects incorrectly classified as innocent) is about 21%. Averaging across studies, guilty suspects are correctly classified as guilty about 76% of the time and innocent suspects are correctly classified about 70% of the time (Ben-Shakhar & Furedy, 1990; National Research Council, 2003). Teachers can also use the polygraph to introduce ethical issues. For example, given this error rate, is it ethical to allow the results of a polygraph to be admitted as evidence in court? And does a polygraph test invade the privacy of the suspect?

Using Brain Activity to Detect Lies

Cognitive neuroscientists have attempted to detect lies by looking into the brain. Whereas the polygraph relies on arousal as a proxy for lying, brain-based methods of detection generally rest on the theory that lying increases cognitive load. Put differently, some neuroscientists assume that the act of lying requires greater mental effort to suppress the truth and to construct a convincing lie. The hope is that technology can detect cognitive load by peering into the brain.

Functional magnetic resonance imaging (fMRI) produces a video image of how much oxygen every area of the brain is using at a particular point in time. This technique has enabled researchers to see which regions of the brain are most active when people are lying. In one set of studies, subjects lying on their back in an MRI machine saw slides of playing cards and then lied about whether they had a particular card in their pocket (Langleben, 2008). When lying, the participants’ prefrontal cortex and the parietal cortex were more active than when they were telling the truth. But there were significant individual differences across participants in the brain areas activated, and other researchers have found that lying activates somewhat different regions (Ganis, Kosslyn, Stose, Thompson, & Yurgelun-Todd, 2003). Researchers have yet to determine whether a particular region of the brain is consistently associated with lying across large groups of participants who are telling the kinds of lies that typically occur in the legal system.

The electroencephalogram (EEG) has also been appropriated as a lie detection device. Some researchers have found a change in brain waves between 250 and 600 ms after participants are presented with a question that requires them to lie (Wolpe, Foster, & Langleben, 2010). Although fMRI, EEG, and other new technologies show some promise, we are still a long way from finding an infallible technology for detecting lies. One persistent problem is that there appears to be no “Pinocchio response”—no physiological set of reactions that is uniquely indicative of lying.

Conclusion

Eyewitness identification and lie detection are just two of many areas in forensic psychology that offer teachers an opportunity to illustrate the important practical applications of basic psychological processes. Teachers in introductory, cognitive, social, developmental, and clinical psychology courses can easily touch on topics in forensic psychology to engage student interest and to help students see the connections between basic and applied science.

Footnotes

Declaration of Conflicting Interests

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author received no financial support for the research, authorship, and/or publication of this article.

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