A brainwave for catching a criminal?

A new study suggests criminals can be detected by measuring a brainwave known as P300. In tests it worked remarkably well, but can we really trust it? 

Mo Costandi  – London Guardian

Terrorists could be identified by a brainwave test that detects concealed information about an imminent attack, according to a study by psychologists from Northwestern University in Chicago.

The test, a sophisticated version of the now-discredited polygraph (or lie-detector) test, is based on the so-called guilty knowledge test developed in the 1950s. Whereas the traditional lie detector test involves asking the suspect whether or not they committed the crime in question, the guilty knowledge test focuses on specific details that would only be known to the perpetrator.

In the 1980s, Peter Rosenfeld combined the guilty knowledge test with recordings of the brain’s electrical activity. He exploited a brain wave pattern called the P300, which occurs in response to visual stimuli after a delay of 300 milliseconds, and can be detected with electrodes attached to the scalp.

It is well known that task-related stimuli, or stimuli that are meaningful in some other way, produce a larger P300 response than others. For the guilty knowledge test, this increased response can be a neurological signature of the unconscious recognition of a familiar object, event, or piece of information.

Rosenfeld’s group has already applied the test in a mock crime scenario, using it to identify participants who had knowledge of a stolen object. In the new study, they applied the test to a mock terrorist situation, recruiting 29 university students and dividing them into “guilty” and “innocent” groups.

The “guilty” group was given a document explaining that they would play the role of a terrorist planning an attack, and containing four different options each for how the attack could be carried out, the types of bombs that could be used, locations in Houston, Texas, that could be targeted, and dates in July on which the attack could be carried out.

Having planned the mock attack, they wrote a letter to an imaginary superior, containing the choices they had made, to aid memorisation of the plan details. The participants in the “innocent” group planned a mock holiday instead.

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