10 May 2000
Language Loss May Improve Ability To Spot Lying
by Kate Melville
Who is best at detecting when someone is lying -- judges? teachers? moms? A study in this week's issue of Nature finds an answer that may be surprising: people with aphasia -- a loss in language ability resulting from a stroke or other type of brain damage -- appear to have a significant advantage in spotting liars, particular when the untruths are given away by changes in facial expression.
Nancy Etcoff, Ph.D., a psychologist at the Massachusetts General Hospital (MGH) who led the study, explains that the phenomenon had been reported previously by neurologists treating people with aphasia but had never been studied in a scientific manner. "As far back as the 1920s there are anecdotal reports of patients with aphasia being able to detect when people were lying," she says. "In the popular book The Man Who Mistook his Wife for a Hat, Dr. Oliver Saks describes a group of patients watching a politician on television and laughing at what they perceived to be his deceptive statements."
To examine the truth of this observation, Etcoff and her colleagues used a series of videotapes prepared by co-authors Paul Ekman, PhD, of the University of California at San Francisco and Mark G. Frank, PhD, of Rutgers University. Volunteers had been videotaped twice talking about their emotional state in a positive way. In one instance they were looking at a pleasant scene and telling the truth, in the other instance they were looking at distressing scenes and lying about their emotional state. Which interview came first on the tape was randomly varied. The tapes had been analyzed previously in Ekman's lab to identify subtle changes in facial expression or changes in vocal pitch associated with the untruthful interview.
For the current study, the videotapes were shown to four groups of participants. One group consisted of patients with significant aphasia as a result of damage to the left sides of their brains. The other groups were patients with right-brain damage and no language difficulty, healthy control subjects and a group of college students. The participants were informed that one of each interviews was untruthful and were asked to identify when the volunteers were lying and when they were telling the truth.
While previous research -- including studies conducted by Ekman -- has shown that people in general have only a 50/50 chance of detecting when someone is lying by their expression or tone of voice, the aphasia patients were able to detect lies cued by facial expression alone 73 percent of the time. The other study groups all had close to 50 percent accuracy in recognizing lies tied to facial expressions. The aphasia patients also did better than the other groups in detecting lies cued by both facial and vocal changes - 60 percent compared with about 45 percent. None of the groups did well in recognizing lies cued by changes in vocal pitch alone.
"One question that may arise when considering these results is whether the patients with aphasia were better at detecting lies or at detecting emotional states," Etcoff explains. "Previous studies have not shown aphasics to be any better than people without brain damage in perceiving simple emotions -- such as happiness or sadness. In fact, because of their aphasia, these patients had impaired ability to understand what the volunteers were actually saying. What they do seem to be more sensitive to are nuances in facial expression that reveal a disconnect between what someone is trying to express and what they really are feeling. We hope to be able to further investigate this fascinating finding."