Washington: Seasoned liars can bluff interrogators with a bland expression for sometime, but then they are unmasked by non-verbal cues.
Researchers examined whether study volunteers could smother facial actions like the twitch of an eyebrow or smiles on command while under scrutiny by a lie catcher.
They could to a degree, but not completely and not always, because non-verbal behaviour can call their bluff, reports the Journal of Nonverbal Behaviour.
The results are derived from frame-by-frame coding of facial movements filmed during an interrogation in which participants, some lying, some telling the truth, were asked to suppress specific parts of facial expressions.
Mark Frank, professor of communication from Buffalo University, supervised and co-wrote the study with former graduate student Carolyn M. Hurley, now research scientist at the US Transportation Security Administration, according to a Buffalo statement.
"As a security strategy, there is great significance in observing and interpreting non-verbal behaviour during an investigative interview, especially when the interviewee is trying to suppress certain expressions," he says.
Hurley and Frank found that these actions can be reduced, but not eliminated, and that instructions to volunteers to suppress one element of expression resulted in reduction of all facial movement, regardless of their implications for veracity.
But the majority of the 60 volunteers reported believing that they had controlled all facial movement and had remained "poker faced" during the interview.
"Behavioral countermeasures are the strategies engaged by liars to deliberately control face or body behaviour to fool lie catchers," says Frank.
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