IN A bar in Maastricht University in the Netherlands, 12 students are each given an envelope marked "Top Secret". Inside are plans for a terror attack somewhere in the country. They must tell no one.
Later, the students are arrested under suspicion of terrorist activities and interrogated using a so-called concealed information test (CIT). Sensors measure skin conductance - moisture levels in their skin. Then mathematical techniques borrowed from artificial intelligence analyse the findings to work out what the students are hiding.
This was of course a mock-up - an experiment carried out in a psychology lab at Maastricht University. But the idea was to show that the new test could one day surpass existing lie detection techniques in ferreting out information from groups of suspects. Traditional lie detectors concentrate on individuals, whereas a group CIT is able to uncover a single piece of information that is being concealed by the entire group, for example, the name of a target city.
Ewout Meijer, who led the experiment, says that many of today's security threats are from terrorist groups involving multiple suspects.
Lie detection techniques usually compare a suspect's responses to a series of questions about a crime against responses to innocuous questions. These responses are recorded via a polygraph, which measures physiological signals, including pulse, respiration rate and skin conductance. But this method is considered unreliable.
Instead, Meijer used a CIT where the aim is to see if a suspect reacts strongly to any particular question in a series of similar ones. In the mock-up, Meijer's team questioned the 12 students while measuring their skin conductance by attaching two small electrodes to their fingers. The students were presented with a battery of queries that listed possible cities, dates, and specific targets for the planned attack, including the correct information for each. They were told to answer "no" to all the questions.
If the suspect is guilty, a question that identifies an element of the plot will elicit an autonomic nervous system response - an arousal response - which is stronger than for other questions in the series. This triggers a spike in both skin conductance and an EEG signal called P300, though this wasn't measured here (see "EEG signals flag up meaning"). An innocent person's physiological responses will trigger no such spikes.
Results from the skin conductance tests were analysed by software containing Bayesian networks, mathematical models that deal with probability, which are the bedrock of artificial intelligence. By comparing the data with the patterns of responses you would expect to find in guilty and innocent subjects, the software determined with high probability that all the suspects knew the attack was planned for 15 August in a particular department store in Rotterdam - the correct answer (Journal of Forensic Sciences, DOI: 10.1111/j.1556-4029.2010.01474.x).
Whether this will translate to real-world terror situations is another matter as analysis is made far more difficult if individuals in a group possess only fragments of information about a planned attack, Meijer admits.
Still, Frank Horvath of Michigan State University in East Lansing, says the technique could be useful for fighting terrorism. "It won't necessitate tactics that we are all familiar with and find distasteful, if not worse," he says.
EEG signals flag up meaning
Peter Rosenfeld of Northwestern University in Evanston, Illinois, and colleagues have pioneered the use of EEG signals in a lie detector test called a concealed information test. They look specifically for a signal called the P300 - which is recorded by placing electrodes on the scalp over the parietal cortex.
"P300 is something that occurs when you recognise something meaningful, in a series of things that are not meaningful," says Rosenfeld.
It is a very effective tool for separating what suspects do and don't know, but Frank Horvath of Michigan State University in East Lansing points out it might not be practical to set up cumbersome EEG equipment in the field.
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