Science/Tech

How to Beat Lie Detector Brain Scans: Suppress Memories of Guilt

Polygraph Tests - Beating Lie Detector Brain Scans - Suppress Memories of Guilt
A new neuroimaging study suggests that, as with polygraph tests, lie detection brain scans are easy to beat if a suspect suppresses memories of criminal guilt. Creative Commons

Companies like No Lie MRI and Brain Fingerprinting Laboratories claim to be able to detect criminal guilt using brain scans of suspects, but a new study finds that such commercial lie detection methods are easy to beat, as long as you can successfully suppress incriminating memories.

The study, conducted by a team of British and German psychologists from the universities of Kent, Cambridge, and Magdeburg, investigated the ability of electroencephalography (EEG) imaging to detect criminal guilt.

 "Brain activity guilt detection tests are promoted as accurate and reliable measures for establishing criminal culpability, said principal investigator Dr. Zara Bergström, of the University of Kent, in a news release.

"Our research has shown that this assumption is not always justified. Using these types of tests to say that someone is innocent of a crime is not valid because it could just be the case that the suspect has managed to hide their crime memories."

Guilt detection brain scans, which the researchers say are now used by law enforcement in countries that include Japan and India, are based on the idea that brain-activity markers of guilt can accurately and reliably reveal whether someone committed a crime.

Much like the now-debunked claims that polygraph tests reveal lies by measuring physical markers like heart rate, this assumption, Bergström's team writes, "relies on the untested assumption that reminders of a crime uncontrollably elicit memory-related brain activity."

The study was published online in the journal Biological Psychology.

Suppressing Guilty Memories During Brain Scans

They debunked this assumption in a series of experiments in which subjects committed a mock crime, and were then encouraged to suppress memories of that crime during an EEG scan.

The participants included 48 healthy German and British individuals, male and female, ranging in age from 18 to 35. They completed a crime simulation task on a computer, in which they vividly imagined being a burglar who stole specific valuable items in houses as image, text, and feedback prompts reinforced their memories about what objects they stole, and how they stole them.

After completing the crime simulation, some of them were trained to mentally block certain memory cues in response to prompts. They then underwent EEG brain scans that assessed their memories of specific parts of the burglary simulation task.

Analysis of the scans revealed that, of the people trained to suppress their crime memories, a significant number were in fact able to intentionally dampen their brain's recognition responses enough to appear innocent.

Should Law Enforcement Rely on Lie Detection Brain Scans?

"Our findings would suggest that the use of most brain activity guilt detection tests in legal settings could be of limited value," said Dr. Jon Simons of the University of Cambridge in the news release.

Most significantly, law enforcement should not assume that brain activity is automatic, since well-trained people can voluntarily evade guilt detection brain scans.

"Of course, there could be situations where it is impossible to beat a memory detection test, and we are not saying that all tests are flawed, just that the tests are not necessarily as good as some people claim," Dr. Simons acknowledged. More research is also needed to understand whether the results of this research work in real life crime detection.'

The researchers said that further research is needed to explain why some people were able to suppress their crime memories better than others, and to find out how generalizable these findings are to real-life crime detection scenarios, or to the results of other brain scanning techniques like magnetic resonance imaging (MRI).

Still, they warn that much like polygraph lie detectors, faith in the validity of guilt detection brain scans is misguided.

"An innocent verdict in a guilty knowledge test could arise because a suspect is truly innocent, because they have forgotten the particular details of the crime that are being tested, or because they are highly motivated to disguise their knowledge and are intentionally suppressing crime memories," the researchers conclude.

 

Source: Bergström Z M, Anderson M C, Buda M, et al. Intentional retrieval suppression can conceal guilty knowledge in ERP memory detection tests. Biological Psychology. 2013.

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