17:41 Tuesday 6th January 2015
BBC Radio Cambridgeshire
CHRIS MANN: Cambridge scientists have helped develop a new lie-detector suit, which helps find out how much you fidget under pressure. This breakthrough has developed a method with a success rate in tests of over 70%. It could be used in police stations around the world within a decade. Professor Ross Anderson of Cambridge University helped develop it and he joins me now. Hello Ross.
ROSS ANDERSON: Hi.
CHRIS MANN: Really interesting, a lie-detector suit. Does it go all over the body?
ROSS ANDERSON: Well in our prototype what we’ve got is a body-motion sensor suit, which is what actors use if they’re acting in cartoons. So you can run around, jump up and down, and the suit records exactly to the millimetre where your arms and legs move. Now in future versions it will be a bit less intrusive, because we’re going to be starting experiments on using W band radar, which is what you get in airport screening, and also in using gesture detection devices such as the Kinect to do the body motion measurements.
CHRIS MANN: Everybody thinks of the polygraph, which I think started in the ’20s, didn’t it? How accurate is it?
ROSS ANDERSON: Well the polygraph can be useful, but it’s got a couple of drawbacks. The first is it’s only slightly better than unaided human judgment of whether somebody is telling truth or lies. It’s a bit over 60% of the time that they get it right, as opposed to about 55% for an unaided human.
CHRIS MANN: So does it mean if we’re looking at someone and said ‘they look a bit shifty’, it’s as good as a polygraph?
ROSS ANDERSON: Well this brings us to the second problem with the polygraph, which is that it doesn’t measure guilty feelings, it measures anxiety. Now most interrogators, when they interrogate someone, make up their mind very very quickly, within the first few seconds, whether the guy is shifty or not, as you put it, and they then look for evidence which confirms their suspicion. And the few people who are really good at telling truth from lies are the people who keep an open mind and keep on looking for more evidence. But if you’re using a polygraph, since it detects anxiety, the temptation is to put the pressure on the suspect as soon as possible and as heavily as possible. It’s like torture but without the thumbscrews. And as we all know from Senator Feinstain’s report into CIA torture, torture basically doesn’t work, because you know the subject will just say what he thinks will stop the pain, and you end up getting a whole lit of false leads. So the beauty about the new technique is that it can be done in an emotionally neutral setting, where you encourage the interviewee to provide more information, and the automation then tells you whether there are guilty feelings associated with particular pieces of information that are volunteered.
CHRIS MANN: So before perhaps people looked for eye-ticks or motions on the face, but actually you’re looking at the whole body now.
ROSS ANDERSON: Yes exactly. So you see we looked at motions of arms, motions of feet. We looked at about seventy different signals that you can extract from full-body motion data. And we found that the reliable estimator was full-body motion. Now what we suspect is happening is this – that if you’re trying to lie to me and I look at your face, you can hold your face and your shoulders still, but you may be twitching in your fingertips, or in your feet. And similarly, if you’re trying to bluff me at poker, you may have a grand smooth sweep of the hand as you shove the chips across the table, but you can be tapping your toes at the same time.
CHRIS MANN: But nervous people will just get found guilty of everything, won’t they? And there are people who are naturally nervous.
ROSS ANDERSON: Well exactly so. And so there are ways that you have to do this; there are ways you have to develop the questioning. And in fact our technique is significantly better at telling truth from telling lies, and so you’d want to turn the questions around, ask questions from different points of view, to make sure that you had zeroed in on what was going on. So a technology like this will drive the questioner to use a much more neutral and much more effective questioning strategy than comes naturally with something like a polygraph.
CHRIS MANN: So the CIA or MI6 could teach the modern successor to James Bond just to freeze their body so that they wouldn’t react.
ROSS ANDERSON: Well exactly. But you see if you freeze, that’s a dead give-away. Now the difficulty, if you want to lie to me, is that you have to fidget at exactly the right level, at exactly the innocent level, rather than at the frozen level or at the higher guilty level. Now there are ways you can do that of course, and some people have got a great ability for self-deception. Many of the world’s greatest salesmen are good at this. They can really believe that this endowment mortgage that they’re about to sell you is the best thing in the world, and it will make you rich. And similarly politicians are sometimes very very good at believing whatever it is that the Civil Service has thought up for them to say today. And if people are suggestible or open to self-deception, so that they really believe they’re telling the truth, then of course it’s going to be difficult for deception-detection technology to pick that up.
CHRIS MANN: Fascinating. Thank you so much. Ross Anderson there, Professor of Security Engineering at Cambridge University. The lie-detector suit.