Polygraph test may not be a good lie-detecting tool

A polygraph test, popularly referred to as a lie detector, may not be a very useful tool to identify when a person is lying, a new study has claimed.

According to Chris Street, from University of Huddersfield in UK, polygraphy purports to work by detecting anxiety.

"But are liars more anxious than truth tellers? The reality is no, because often the reason we lie is that to tell the truth would be very difficult and more anxiety-provoking than a lie," he said.

To gather data about how humans lie, participants being studied should not be aware that they are taking part in experiments that are dealing with the subject of truth and lies, researchers said.

The researchers devised a deception of their own that involved hiring a film studio in London and persuading passers-by to be interviewed for a "documentary" on tourism.

They were told by 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 experiment 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.

Street and his co-researcher and author Daniel Richardson, of University College London, have developed a different explanation.

"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.

The study was published in the Journal of Experimental Psychology: Applied.