An international team of psychologists has shown that some people can suppress incriminating memories and avoid detection by brain activity measured by guilt detection tests.
Law enforcement agencies use the tests, which are based on the idea that criminals will have stored specific memories of their crime.
Once presented with reminders of their crime in a guilt detection test, it is assumed that the criminal’s brain will automatically and uncontrollably recognize these details, with the test recording the brain’s “guilty” response.
In the new research, psychologists at the universities of Kent, Magdeburg and Cambridge, and the Medical Research Council, proved that some people can intentionally and voluntarily suppress unwanted memories.
This ability to control brain activity, thereby suppress or even abolishes brain activity related to remembering.
Researchers conducted a series of experiments in which people who conducted a mock crime were later tested on their crime recognition while having their electrical brain activity measured.
Investigators found that when asked to suppress their crime memories, a significant proportion of people managed to reduce their brain’s recognition response and appear innocent.
Experts say that this finding has major implications for brain activity guilt detection tests. We now understand that those using memory detection tests should not assume that brain activity is outside voluntary control.
Furthermore, any conclusions drawn on the basis of these tests need to acknowledge that it might be possible for suspects to intentionally suppress their memories of a crime and evade detection.
Zara Bergstrom, Ph.D., 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.”
However, not everyone can beat the test, and more research is necessary to determine test validity.
Michael Anderson, Ph.D., a senior scientist at Cambridge, said his group is presently trying to understand such individual differences with brain imaging.
Jon Simons, Ph.D., 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.”
Source: University of Cambridge