• Dr. Timothy Smith

Can Science Detect Liars?

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Who has not wondered whether someone else has told the truth or not? Many recognize classic telltale signs such as avoiding eye contact to determine the veracity of another’s words. The traditional polygraph, or lie detector test, measures heart rate, breathing rate, blood pressure, and perspiration. In general, when people lie, their pulse jumps, respiration and blood pressure increase, and they begin to sweat. The polygraph measures changes in each of these indicators in relation to normal or baseline measurements taken when responding to known true questions. When someone lies, the polygraph records readings that deviate from the baseline. Although used routinely by the FBI and other law enforcement agencies to determine the truth of people’s statements, courts do not accept polygraph results as evidence because the results cannot be relied on as evidence and are not scientifically sound.

Research by the psychologist Leonard Saxe summarized in a paper published in American Psychologist in 1991 describes an experiment conducted by the television news show “60 Minutes” to see if polygraph examiners could detect the identity of a thief in the TV studio. The experiment demonstrated that each of the four polygraph examiners picked a different person as the thief showing the lack of consistency in polygraph data and interpretation. The US Supreme Court cited Saxe’s research in the case of US v. Scheffer in 1998 to highlight the unreliability of the polygraph. In that case, the Supreme Court ruled for the first time that the polygraph could not be used as evidence in a court of law.

Little hard science has accumulated around using body language or facial expression to determine a person’s state of mind, including differentiating whether a statement rings true or false. Dr. Paul Ekman, a renowned American psychologist, developed a large body of research into the relationship between emotions and facial expressions. His work focused on cataloging thousands of human facial expressions and mapping them to various emotions. Ekman pioneered the field of micro expressions. In short, micro expressions constitute very brief expressions that flash across people’s faces in 1/25 of a second. These expressions occur so quickly that they can only be visualized using slow motion photography. Ekman suggests that these micro expressions arise involuntarily and that they have universal meanings across people from around the world. Based on his research and cataloging the meaning of the expressions, the TSA developed a training system called SPOT which stands for Screening of Passengers by Observation Techniques to screen for terrorists. The program uses a variety of body language cues to determine if a passenger at the airport poses the risk of being a terrorist. Sharon Weinberger notes in an article published about SPOT in the prestigious journal Nature on the 26th of May 2010 that “growing number of researchers are dubious — not just about the projects themselves, but about the science on which they are based.” Weinberger further notes that faces do express emotion, but the connection to truthfulness does not extend to facial expressions.

People for millennia have sought to figure out by body language, especially to find out whether someone could be trusted to tell the truth. Some attributes such as posture, eye contact, or perspiration often lend clues about someone’s truthfulness. Machines such as the polygraph use additional involuntary responses such as respiration and heart rate to differentiate truth from fiction. Moreover, a more in-depth analysis of human facial micro expression has been linked to human emotional states. With all the activity and excitement around lie detection, little scientific evidence supports the attribution of these clues to truthfulness. It appears enticing to listen to a body language expert or polygraph administrator dissect a testimony for veracity, but the truth remains that science does not back up their conclusions. For that reason, courts do not accept polygraphs, and you should be skeptical of connecting body language to the truth.

Dr. Timothy Smith

Dr. Smith’s career in scientific and information research spans the areas of bioinformatics, artificial intelligence, toxicology, and chemistry. He has published a number of peer-reviewed scientific papers. He has worked over the past seventeen years developing advanced analytics, machine learning, and knowledge management tools to enable research and support high level decision making. Tim completed his Ph.D. in Toxicology at Cornell University and a Bachelor of Science in chemistry from the University of Washington.

You can buy his book on Amazon in paperback and in kindle format here.

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