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Extreme physical exertion in a threatening situation lasting just 60 seconds can "seriously damage" the memories of those involved, according to a new study of police officers.
Police officers, witnesses and victims of crime suffer loss of memory, recognition and awareness of their environment if they have to use bursts of physical energy in a combative encounter.
This can occur in situations such as an officer chasing a fleeing suspect, according to Lorraine Hope of the University of Portsmouth.
She said that her findings, published in Psychological Science, are a warning of the problems with witness statements to the courts.
"Police officers are often expected to remember in detail who said what and how many blows were received or given in the midst of physical struggle or shortly afterwards.
"The results of our tests indicate it may be very difficult for them to do this.
"As exhaustion takes over, cognitive resources tend to diminish. The ability to fully shift attention is inhibited, so even potentially relevant information might not be processed.
"Ultimately, memory is determined by what we can process.
"The legal system puts a great deal of emphasis on witness accounts, particularly those of professional witnesses like police officers.
"Investigators and courts need to understand that an officer who cannot provide details about an encounter where physical exertion has played a role is not necessarily being deceptive or uncooperative.
"An officer's memory errors or omissions after an intense physical struggle should not unjustly affect his or her credibility."
The team of researchers tested 42 male and 10 female fit and healthy police officers in Winnipeg, Canada, for the study.