Encyclopedia of Psychology and Law

speech). Laboratory research has more or less consis-

tently revealed that, despite people’s stereotypes of

lying behavior, liars are stiller than truth tellers and

able to maintain eye gaze. This indicates that behav-

ioral control and cognitive load may be more overpow-

ering mechanisms than emotional arousal in the

low-stakes liar. One would expect then that in a higher-

stakes lying situation, emotions are likely to run

higher. Although this might be the case, it would

appear that the desire to appear credible (controlling

behavior) and the cognitive load associated with telling

a higher-stakes lie increase even more so, since

research into the behavior of high-stakes liars such as

suspects in police interviews reveals similar patterns in

behavior to laboratory research subjects, with the addi-

tion of a decrease in blinking and an increase in speech

pauses.

If high-stakes liars behave similarly as low-stakes

liars (in that, on the whole, they display signs of

increased cognitive load and increased control rather

than nervousness), then could their lies be any easier

to detect? As mentioned earlier, people expect certain

behaviors of a liar, yet these behaviors often fail to be

displayed. This is one reason why most people do not

score above the level of chance when trying to detect

people’s lies in experiments. In contrast, in experi-

ments where police officers were shown clips of

real-life liars and truth tellers (suspects in police inter-

views) and asked to make veracity judgments, the

overall accuracy was more than 65%. Why it is higher

is unclear. It could be that the situation that observers

were being asked to judge was more contextually rel-

evant to them than, for example, watching students

who have been asked to lie or tell the truth about triv-

ial matters. It could be that observers were able to

make use of the signs of increased cognitive load that

the suspects did reveal (increased pauses in speech,

bodily rigidity, etc.) or perhaps that they were able to

pick up on something less tangible.

Samantha Mann and Aldert Vrij

Further Readings

DePaulo, B. M., Lindsay, J. L., Malone, B. E., Muhlenbruck,

L., Charlton, K., & Cooper, H. (2003). Cues to deception.

Psychological Bulletin, 129,74–118.

Mann, S., Vrij, A., & Bull, R. (2002). Suspects, lies and

videotape: An analysis of authentic high-stakes liars. Law

and Human Behavior, 26,365–376.

Mann, S., Vrij, A., & Bull, R. (2004). Detecting true lies:

Police officers’ ability to detect deceit. Journal of Applied

Psychology, 89,137–149.

DEVELOPINGCOMPREHENSIVE

THEORIES OFEYEWITNESS

IDENTIFICATION

See WITNESS MODEL

DIMINISHEDCAPACITY

Diminished capacity refers to two distinct doctrines.

The first, known as the mens rea variant,refers to the

use of evidence of mental abnormality to negate a

mens rea—a mental state such as intent, required by

the definition of the crime charged (the mens rea vari-

ant). The second, known as thepartial responsibility

variant,refers to the use of mental abnormality evi-

dence to establish some type of partial affirmative

defense of excuse. Courts have used various other

terms, such as diminished responsibility, to refer to

one or both of these distinct doctrines, but the term

used is unimportant. Confusion arises, however, when

the two types of doctrine are not clearly distinguished.

Neither entails the other, and distinct legal and policy

concerns apply to each.

The Mens Rea Variant

Mental abnormality can negate mens rea, primarily in

cases in which the disorder is quite severe and pro-

duces a cognitive mistake. For example, in Clark v.

Arizona (2006), a recent case that reached the

Supreme Court of the United States, the defendant

claimed that he believed that the police officer he

killed was really a space alien impersonating a police

officer. If this was true, the defendant did not intendto

kill a human being with the knowledgethat the victim

was a police officer. Historically, the legal objection to

using mental abnormality to negate mens rea was that

traditional doctrine required that mistakes had to be

objectively reasonable and a mistake that mental

abnormality produces is definitionally unreasonable.

Thus, evidence of such mistakes was excluded, even

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