How Well Do We Really Remember A Crime Scene?

Imagine that, upon arriving home one day, you spot someone trying to break into your house. When you shout, the thief suddenly flees. Being the vigilante type, you decide to pursue him, racing down the street and climbing over a fence. Unfortunately, the thief gets away, but a few hours later, police call you to report they’ve apprehended someone nearby on suspicion of a similar crime. Called into the station, you’re asked to identify the criminal from a lineup.

Can you do it? A new study published in Psychological Science suggests that, no matter how sharp you think your memory is, you might not do as well as you think.

Researchers from the University of Portsmouth in Canada and elsewhere put Winnipeg police officers through a battery of experiments to determine just how well they were able to remember events while under duress. The results were startling: Just 60 seconds of intense physical exertion—such as running, combat, wrestling or other activities—was enough to severely impair their ability to recall faces, information and details about the environment.

The experiment involved 52 police officers who had an average of eight years on the job and were deemed to be in good physical condition. First, they were briefed on a recent wave of robberies, including details on what the thieves looked like and other patterns. Then, half the officers were told to engage in a “full-force attack” on a 300-pound water bag—punching, kicking and tackling the dummy until they had reached physical exertion—while the other half, a control group, observed quietly. Afterward, both groups entered a trailer of a “known criminal,” where they encountered an actor who shouted at them to leave the property.

The findings indicated that, as a whole, the officers who had physically exerted themselves remembered less about the “known criminal,” less from the initial briefing, and made more memory-recall errors overall. En route to the trailer, both groups had incidentally encountered another actor, and while more than 90 percent of the non-exerted officers could provide some descriptive information about his appearance, barely a third of the experimental group remembered him at all.

Perhaps most important, the officers’ ability to correct identify the “known criminal” in a lineup differed significantly. The non-exerted officers provided much more detailed descriptions of the individual, and were twice as likely to correctly identify him from a photo lineup with five similar-looking people.

Although the researchers don’t fully understand why the physical exertion had such an impact on the officers’ recall ability, they believe it relates to a cap on the mind’s overall capacity for paying attention to stimuli. “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,” said Lorraine Hope, the lead author of the study.

These findings are far from academic—they are highly relevant to the criminal justice system and the methods by which we investigate and prosecute crimes. Hope notes:

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….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.

In contrast to the overall trend, though, the exerted officers were equally good at recalling one specific type of detail: information about a potential threat. Although the “known criminal” was unarmed, the trailer contained a number of weapons within easy reach, including an M16 carbine, a revolver and a large kitchen knife. Despite the limited ability to pay attention to and remember details after intense physical activity, it seems we notice the things that might cause us harm.

Joseph Stromberg | | READ MORE

Joseph Stromberg was previously a digital reporter for Smithsonian.