Police and intelligence agencies around the world have, for almost 100 years, relied on lie detectors to help to convict criminals or unearth spies and traitors. But the polygraph could soon be defunct.
Researchers in Britain and the Netherlands have made a breakthrough, developing a new method with a success rate of more than 70% in tests that could be in use in police stations around the world within a decade.
Rather than relying on a few facial tics, talking too much or waving of arms – all seen as tell-tale signs of lying when being interviewed – the new method involves monitoring full-body motions to provide an indicator of guilty feelings.
The polygraph is widely used in the United States in criminal and other cases for the FBI and CIA. There has been a lot of scepticism in scientific and legal communities about its reliability but the new method developed by the researchers has performed well in experiments.
The basic premise is that liars fidget more and that the use of an all-body motion suit, the kind used in movies for helping to create cartoons, will pick this up. The full-body suit contains 17 sensors that register movement up to 120 times a second in three dimensions for 23 joints.
The findings were set to be published at an international conference on system sciences opening at Kauai, Hawaii, on Monday this week.
One of the academics, Ross Anderson, professor of security engineering at Cambridge University, said: “Decades of deception research show that the interviewer will tell truth from lies only slightly better than random, about 55 out of 100.
“The polygraph has been around since the 1920s and by measuring physiological stress induced by anxiety you can get to 60. However, it can easily be abused as an interrogation prop and, anyway, many people are anxious facing a polygraph on which their job or liberty depends.”
He said the new method, by contrast, achieved a reliability rating of more than 70% and he was confident they will be able to do better. In some tests, they have already achieved more than 80%. “The takeaway message is that guilty people fidget more and we can measure this robustly.”
Anderson added that the research had a special significance at this time, against the background of the US Senate report on torture by the CIA. “We have known for a long time that torture does not work.”
Apart from the moral case against torture, the new method offers an alternative, pragmatic way to conduct interviews. The research paper was written by Anderson, Dr Sophie van der Zee, also of Cambridge University, Professor Ronald Poppe of Utrecht University and Professor Paul Taylor of Lancaster University.
The polygraph, created in 1921 by a student in California and a policeman, records changes in pulse, sweating and breathing.
But the Supreme Court in 1998 ruled there was no consensus that the polygraph is reliable, a finding supported by the National Academy of Scientists in 2003. In spite of this, it is still widely used in the US. It is much less popular in Europe.
The experiment carried out by Anderson and his colleagues involved 180 students and employees at Lancaster University, of which half were told to tell the truth and half to lie. They were each paid £7.50 for their participation in the 70-minute experiment, involving two tests.
Some were interviewed about a computer game, Never End: they played it for seven minutes whereas the others lied about playing it, having only been shown notes about it.
The second test involved a lost wallet containing £5. Some were asked to bring the wallet to a lost-and-found box whereas the others had to hide it and lie about returning it.
“Overall, we correctly classified 82.2% (truths: 88.9%, lies: 75.6%) of the interviewees as either being truthful or deceptive based on the combined movement in their individual limbs,” the report said.
Anderson said: “Our first attempt looked at the extent to which different body parts and body signals indicated deception. It turned out that liars wave their arms more, but again this is only at the 60% level that you can get from a conventional polygraph.
“The pay dirt was when we considered total body motion. That turns out to tell truth from lies over 70% of the time, and we believe it can be improved still further by combining it with optimal questioning techniques.”
Another advantage is that the total body motion is relatively unaffected by cultural background, anxiety and cognitive load (how much you are thinking) that confound other lie-detection technologies, Anderson said. The use of all-body suits is expensive – about £30?000 – and can be uncomfortable: Anderson and his colleagues are looking at low-cost alternatives.
He acknowledged that agencies, such as the CIA, could teach agents how to counter the full-body motion method by freezing their bodies, but said that in itself would be a giveaway. – © Guardian News & Media 2015
Ewen MacAskill is the defence and security correspondent for the Guardian.