Spotting the liar in the witness box – how valuable is demeanour evidence really? (2)

Abstract

In the previous part of this contribution I discussed the history of so-called “demeanour evidence” and its current role in the law of evidence. I furthermore examined the extensive empirical evidence that shows that demeanour – as a means of accurate and reliable credibility assessment and decision-making in litigation – essentially is worthless. Human lie detection is fraught with difficulty. It is predicated upon a multitude of misconceptions about how liars behave, including specific verbal and nonverbal cues commonly believed to indicate dishonesty. Below I continue with an analysis of the social science research data on veracity judgments based on demeanour in order to attempt to answer the question: Why are human beings such poor lie detectors? Next I expound upon the reasons why lie detection in court might actually be more difficult than in a laboratory setting. I then explore the potential impact of empirical findings upon the principle of appellate deference to credibility findings of first instance. I conclude by addressing the question regarding the appropriate response of the legal system in the face of the overwhelming research data on the lack of reliability of so-called “demeanour evidence”.