Scientists reveal how easy it is to trick a lie-detector test

It’s often described as one of the most accurate lie detector tests, but a new study suggests that fMRI tests can easily be tricked.

The brain imaging technique tracks blood flow around the brain, from which experts can deduce whether someone is lying.

Now, researchers from the University of Plymouth have revealed two ‘simple’ ways that people can trick these tests.

Dr Chun-Wei Hsu, who led the study, said: "fMRI tests are not currently used by law enforcement in the same way as polygraph tests, but they have been considered for scientific and criminal use as a way of detecting when someone is concealing information.

“This study shows that the process can be manipulated.”

In fMRI lie detector tests, a person is shown information, with the assumption that their brain will be more activated when they’re presented with the lie.

This means that more blood flows to the brain, revealing the lie in the brain scan.

In the study, the researchers asked 20 participants to conceal information about a ‘secret’ digit they saw inside an envelope, before teaching them two ways to trick the brain scans.

The first technique was to associate meaningful memories to items they weren’t trying to hide, making them seem more significant.

The second technique was to focus on the superficial aspects of the item they were trying to conceal, making it seem less significant.

Results revealed that these techniques lowered the accuracy of the fMRI test by around 20 per cent.

Dr Hsu added: "None of our participants were seasoned liars or criminals, they were just everyday people, so before this test can even be considered for forensic use, there must be further studies carried out to help identify when someone is using mental countermeasures.

"Deception is a really challenging area of psychology, and the more we can find out about the techniques used to detect it, the better."