London: Scientists have shown that the lie-detector test that uses a brain imaging technique can be deceived by the using simple mental countermeasures.
The research suggests that more needs to be done to detect these countermeasures to make brain imaging more reliable for forensic applications.
People have certain physical ‘tells’ when they conceal information — and studies show that good liars can prevent these ‘tells’ being detected by displaying physical red herrings of their own.
Researchers from the University of Plymouth in the UK and University of Padova in Italy, have shown that even a brain imaging technique called functional Magnetic Resonance Imaging (fMRI), which in theory is much harder to trick, can be beaten by people who use two particular mental countermeasures.
The research, published in the journal Human Brain Mapping, is the first to explore the effects of mental countermeasures on brain activity in fMRI. It showed that when people used the countermeasures, the test proved to be 20 per cent less accurate.
Concealed information tests work because a person who is hiding something will ‘give away’ what they are concealing when faced with it in a list. For example, if a thief has stolen a diamond ring, the ring will be more striking to the thief than similar control items such as necklaces and bracelets — and the thief will show physiological signs that reveal their guilt.
However, these tests based on physiological signs are easy to beat as perpetrators can artificially alter them when seeing a control item, therefore confusing the test. To overcome this problem, researchers moved to methods that look directly at brain activation using fMRI. An fMRI machine tracks blood flow to activated brain areas.
The assumption in concealed information detection is that the brain will show signs of recognition when presented with the concealed items while exerting extra effort to conceal signs of such recognition, and so the brain regions that do more work will get more blood.
Such regions light up in scans, and they are primarily involved in directing attention and in decision making.