Police often resort to lie detector or polygraph test to find out the truth in certain high-profile cases. But is the test really useful? No, says a British psychology researcher.
Dr Chris Street, an investigative psychology lecturer at the University of Huddersfield and lead author of the study, said it has traditionally been said we should trust our hunches and unconscious knowledge of body language to detect whether someone is lying or not.
However, Street’s research suggests people are better off consciously relying on a single “cue” to tell if someone’s nose is growing, such as whether or not a person is “plainly thinking hard.”
Research assistants placed outside the studio that the film makers were running out of time and asked if, in addition to describing genuine travel experiences, they would talk about places they had not actually visited.
Inside the studio, the speakers were then interviewed by a director who – they supposed – was unaware that they had agreed to lie on film.
The sequence of filmed interviews that resulted from the e
xperiment constitutes a valuable body of material that is being made available to other researchers in what is still the relatively new field of human lie detection, researchers said.
For more than 30 years, the standard approach to tapping the unconscious has been to use the “indirect lie detection” method.
“People are asked to rate some behaviour that is indirectly related to deception,” said Street.
“For example, does the speaker appear to be thinking hard or not? The researcher then converts all thinking-hard judgements into lie judgements and all not-thinking-hard judgements into truth judgements,” he said.
The fact that these indirect judgements give better accuracy than asking people to directly and explicitly rate statements as truth or lies has been taken as evidence that people have innate, unconscious knowledge about human deception.
“Indirect lie detection does not access implicit knowledge, but simply focuses the perceiver on more useful cues,” the researchers said.
It is an argument that could have real-world significance, in the training of interrogators, for example.
British Psychological Society is one body that has dismissed the polygraph as a tool that will never be useful, said Street.
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