A Primer in Lie Detection

How do neuropsychologists and clinical psychologists determine when someone is lying? First it is important to know the three diagnostic subgroups of individuals who distort their symptoms:

Malingerers are individuals who consciously fake, exaggerate or distort their symptoms for some external reward or objective gain. They are aware that they are lying and also of the reason they are doing so.

Factitious Disorder is a psychological disorder where an individual may feigh physical signs or symptoms because he or she is motivated to assume the sick role. Unlike malingerers an individual exhibiting this disorder lacks conscious external incentives for the behavior, such as economic gain or avoiding legal responsibility. While people with factitious disorders are aware that they are faking their symptoms, their motivation to assume the sick role is largely unconscious.

Conversion Disorder is a psychological disorder where people experience motor or sensory symptoms that are psychological in origin and cannot be explained by a medical condition. These folks experience their symptoms as real, and consequently they suffer. They are not consciously aware of producing the symptoms or of any motivation or secondary gain.

When psychologists evaluate an individual, they draw on extensive data, never relying on a single test or observation. All inforamtion is interpreted within the context of : (1) consistency within the history of the examinee, (2) the likelihood that the symptoms and complaint make medical sense and fit the disease pattern, (3) an understanding of the present situation, psychosocial history, and emotional predisposition of the examinee, and (4) consideration of the emotional reactions of the examinee to his/her symptoms. Malingering and factitious lying is picked up by neuropsychological tests because the examination is complex and makes diagnoses based on analyzing complex patterns of behavior--not one or two obvious symptoms. "Conversion reactions" present themselves differently than true organic brain injury and are readily differentiated by neuropsychological clinicians.

In addition to test data, information from the clinical interview helps assess the truthfulness of examinees. Lying results in behaviors that provide:

Verbal cues

People who lie make subtle changes in their speech patterns including

  • inappropriate pronoun substitutions
  • confused tenses
  • over-generalizations
  • overly complex details to mask the lie

Physical cues

Lying can result in increased stress, as manifested by

  • increased pulse
  • increased body temperture
  • increased involuntary eye movements
  • changes in eye contact
  • decreased focus

Psychologists and neuropsychologists rely on direct observation, understanding of the differing etiologies of lying and extensive test data to detect malingering. Once faking or distortion has been detected, the next step is to untangle the complex motivations and determine legitimate functional impairments.

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