Just 60 seconds of all-out physical exertion in a threatening situation can seriously damage the memories of those involved, including police officers, witnesses, and crime victims, according to a new study.
Researchers, led by Dr. Lorraine Hope of the University of Portsmouth, found that less than 60 seconds of all-out exertion can seriously impair their ability to remember details of the incident — or even identify the person who was involved.
An example of all-out physical exertion might be when a police officer is forced to chase down a fleeing suspect or engage in a physical skirmish with a criminal. Even people in top physical condition are not immune to the rapid drain of cognitive faculties, researchers noted.
“Police officers are often expected to remember in detail who said what and how many blows were received or given in the midst of a physical struggle or shortly afterwards,” said Hope, a reader in applied cognitive psychology in the university’s department of psychology.
“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 attended to. Ultimately, memory is determined by what we can process and attend to.
For the study, researchers recruited 52 police officers in Winnipeg, Canada, including 42 males and 10 females, with an average of eight years on the job. All officers were fit and healthy and engaged in regular exercise.
During an initial briefing, the officers were given background information about a recent spate of armed robberies in the city. The briefing included details of how the robberies were conducted and witness descriptions of the perpetrators. Half of the officers then engaged in a full-force physical attack on a 300-pound hanging water bag, while those in the control group were assigned as observers.
Officers continued the assault on the bag until they no longer had strength to keep going or until they were breathless and struggling to continue.
The next part of the test required the police officers to approach a trailer that a “known criminal” was suspected of occupying. On entering the trailer, the officers found themselves in a realistic living area where a number of weapons, including an M16 carbine, a revolver, a shotgun, and a large kitchen knife were visible.
After a short delay, a “target individual” emerged from another room and shouted aggressively at the officer to get out of his property.
Hope found those who had been asked to exert themselves physically remembered less about the target individual and made more recall errors compared to the control group. The officers who had been exerted also recalled less about the initial briefing information and what they did report was less accurate.
Officers who had been exerted also reported less about an individual they encountered incidentally while en route to the trailer. While more than 90 percent of non-exerted observers were able to recall at least one descriptive item about him, barely one-third of exerted officers remembered seeing him at all.
Everyone remembered seeing the angry suspect in the trailer, but non-exerted observers provided a significantly more detailed description of him and made half as many errors in recall as those who were exhausted. These observers were also twice as likely to correctly identify the suspect from a line-up.
One striking aspect of the findings showed that exerted officers were able to register threat cues in the environment to the same degree at non-exerted officers.
“The legal system puts a great deal of emphasis on witness accounts, particularly those of professional witnesses like police officers,” she continued.
“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.”