法医学研究ジャーナル

Catching Liars: Why it can be so Hard

Abstract

Shawn Adair Johnston

Considerable research reveals that most people, including mental health and law enforcement professionals, are remarkably poor at catching liars, doing no better than chance. Our comparative inability to detect deception poses a profound threat to the reliability of forensic psychological and psychiatric evaluations of criminal defendants intended to assess such things as current mental status and future dangerousness. In forensic evaluations, where one’s personal freedom, even life, can be at stake, some clients, perhaps more than some, will inevitably dissemble. This essay provides a brief and non-technical description of the research my students and we have conducted designed to better understand the reasons for which detecting deception is so difficult. In this regard, and consistent with much previous research, we discovered that in assessing the verbal content of other persons’ statements, it is possible with a good degree of reliability to differentiate between true and deceptive statements of criminal defendants. We also found that the “truth” is itself a multidimensional concept and that truthful versus false statements differ with regard to both the quantity and quality of information contained in a statement. While multiple challenges exist to accurately detect deception, our data strongly suggested that it may be so difficult to catch liars because it requires more cognitive work to identify false rather than true statements. Indeed, the data indicate that determining a statement is true appears to involve a one-step cognitive process while determining a statement is false appears to involve a two-step cognitive process, whereby a false statement is recognized as lacking attributes of truthfulness while simultaneously manifesting attributes of deception. That it would be more difficult to recognize falsehoods and require more cognitive work does not seem surprising considering that the identification of a lie forces us to look below and reject the surface meaning of a statement concluding that the statement is not simply inaccurate but actually intended to deceive or mislead us. On a more positive note, even though deception is ubiquitous in human relationships and a significant number of dangerous liars will be successful, the accuracy of deception detection can be improved by the application of the findings from verbal content analysis identifying those statement attributes characteristic of truthfulness versus deception. It would seem especially important for forensic psychologists and psychiatrists to be aware of research capable of assisting them in assessing the veracity of criminal defendants participating in court-ordered evaluations.