Research calls into question reliability of such tests

Our findings would suggest that the use of most brain activity guilt detection tests in legal settings could be of limited value.

Dr Jon Simons, Department of Psychology at the University of Cambridge

Brain scans that claim to be able to determine whether a criminal is guilty of a crime can be fooled, new research reveals.

The study has shown that people can intentionally suppress incriminating memories and thereby avoid detection in brain activity guilt detection tests.

Such tests, which are commercially available in the United States and are used by law enforcement agencies in several countries, including Japan and India, are based on the logic that criminals will have specific memories of their crime stored in their brain. When presented with reminders of their crime, it was previously assumed that their brain would automatically and uncontrollably recognise these details. Using scans of the brain’s electrical activity, this recognition would be observable, recording a ‘guilty’ response.

However, research by an international team of psychologists from the universities of Cambridge, Kent and Magdeburg as well as the Medical Research Council, has shown that some people can intentionally and voluntarily suppress unwanted memories.

For the study, the researchers had participants conduct a mock crime. These people were later tested on their crime recognition while having their brain activity monitored using electroencephalography (EEG). Critically, when asked to suppress their crime memories, a significant proportion of people managed to reduce their brain’s recognition response and appear innocent.

If suspects can intentionally suppress their memories of a crime and evade detection, the research calls into question the reliability of brain activity guilt detection tests, and suggests careful consideration is needed before such evidence is introduced in criminal trials.

Dr Zara Bergstrom, formerly with the University of Cambridge and currently a lecturer in cognitive psychology at the University of Kent and principal investigator on the research, said: “Brain activity guilt detection tests are promoted as accurate and reliable measures for establishing criminal culpability. 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.”

Dr Jon Simons, of the Department of Psychology at the University of Cambridge, added: “Our findings would suggest that the use of most brain activity guilt detection tests in legal settings could be of limited value. 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. More research is also needed to understand whether the results of this research work in real life crime detection.”

Dr Michael Anderson, Senior Scientist at the Medical Research Council Cognition and Brain Sciences Unit in Cambridge, commented: “Interestingly, not everyone was able to suppress their memories of the crime well enough to beat the system. Clearly, more research is needed to identify why some people were much more effective than others.”

Dr Anderson’s group is presently trying to understand such individual differences with brain imaging.

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