Vincent Denault

Assessing credibility through body language

avril 13 2016 13 avril 2016

“Each charge presented against Mr. Ghomeshi is based entirely on the evidence of the complainant. Given the nature of the allegations this is not unusual or surprising; however it is significant because, as a result, the judgment of this Court depends entirely on an assessment of the credibility and the reliability of each complainant as a witness.”

That statement by Justice William B. Horkins was central to Jian Ghomeshi’s acquittal on sexual assault charges in March.

Leaving aside the debate around false memories, the ruling is an opportunity to revisit some questions about our justice system’s ability in assessing the credibility of witnesses.

Are police officers, prosecutors and trial judges well equipped and knowledgeable enough on this count? Research suggests that they are probably not. The science shows that there is no known pattern of behaviour that is entirely reliable when trying to detect whether people are lying, or for that matter when they are telling the truth.

Unfortunately, the research also suggests that legal professionals approach lie detection and credibility in a manner that fits poorly with the current state of scientific knowledge. At least some aspects of the credibility assessment of witnesses in the courtroom should raise concerns. Visual characteristics such as a witness’ skin colour  or facial traits can have an impact on sentencing outcomes. False beliefs about lie detection can also lead to biased assessments. According to the Dangerous Decision Theory, being too highly motivated to spot the difference between what’s real and what’s fake can exacerbate the incorrect interpretation of a testimony.

However, according to the Supreme Court, when it comes to credibility assessment, the trial judge “not only hears the evidence but also has the great advantage of watching the demeanour of all who testify”, an advantage so important that “in the absence of a palpable and overriding error by the trial judge, his or her perceptions should be respected.” In other words, the country’s top court accepts the view that the demeanour of witnesses plays a huge part in assessing credibility, and that trial judges possess the skills to understand nonverbal communication.

There’s no question that demeanour plays a huge part in that assessment in the courtroom. Trial judges will also scrutinize the body language of those who are not testifying to see how they react to a witness’ statements. These observations can have either a positive or negative effect on credibility and the outcome of the trial. Some courts explicitly guard against relying on a witness’ demeanour in the court, when he or she is not testifying. Even so, these impressions can filter, albeit unconsciously, to the trial judge’s assessment.

If the impact of nonverbal communication on credibility assessment leaves no doubt, the accuracy of the trial judge’s interpretation of witnesses’ demeanour is less clear. For example, Leif A. Stromwall and Par Anders Granhag, demonstrated in a paper published in 2003 that law professionals assume incorrectly that behaviours such as averting one’s gaze are reliable measures to detect lies. I myself have argued that comments by trial judges about nonverbal communication have little to no apparent connection with the current state of scientific knowledge. Without having even identified specific behaviours, some trial judges will conclude that the nonverbal communication of a witness reflects a specific state of mind they think is directly associated with truthfulness or dishonesty. Trial judges will also comment specific behaviours as if they were telltale signs of deceit. So if a witness has the misfortune to smile, to look, to shrug, to frown, to blush or hesitates at the wrong moment, that is the moment where the trial judges think that such behaviours should not be displayed, his or her credibility can be affected. Combined with other evidence, changes in the rhythm of a witness’ testimony or in the tone of his or her voice can ultimately affect the trial’s outcome.

Assessing credibility in the courtroom is no easy task. And yet it “is an issue that pervades most trials, and at its broadest may amount to a decision on guilt or innocence,” Justice Binnie wrote in 2002. Debunking common misconceptions held trial judges, prosecutors and police officers should be a priority.

Having said that, while it is true that body language is not always reliable in detecting lies and deception as easily as Pinocchio’s nose, it would be wrong to say it should be ignored at trial. Ultimately, understanding someone is informed by human communication, which is both verbal and nonverbal. The trial as a whole is much more than simply an exercise in lie detection.

Vincent Denault is a Montreal-based lawyer and non- verbal communications consultant

Photo licensed under Creative Commons by discoodoni

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Vincent Denault is a Montreal-based lawyer and consultant. His practice and research focus on nonverbal communication, credibility assessment, and deception detection. He is a lecturer and doctoral student at the University of Montreal’s Department of Communication and the codirector of Montreal’s Center for Studies in Nonverbal Communication Sciences.

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