New FSI Study: Memory Is Worst About Most Critical Moment Of An OIS

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A profound irony is revealed in a major new study of human performance under stress, sponsored by the Force Science Institute.

Namely: At the most critical moment in a force encounter–the moment that perhaps is most important for an officer to describe accurately–the officer’s memory of certain key details about what happened is likely to be the least reliable.

In particular, the first-of-its-kind study documents that officers actively involved in armed confrontations often have difficulty accurately answering questions about a suspect’s weapon, including whether a weapon was visible in the offender’s hand, how the weapon was presented, and even whether the suspect fired it during the incident.

A peer-reviewed report on the study has been accepted for publication by the American Psychological Assn.’s prestigious journal, Law and Human Behavior. This will be the eleventh peer-reviewed scientific journal to have published law enforcement-related studies by the Force Science Institute.

An international team that included Dr. Bill Lewinski, FSI’s executive director, conducted the research. Lead author of the findings is Dr. Lorraine Hope, a professor of applied cognitive psychology at the University of Portsmouth in England. (Dr. Hope led another landmark FSI study several years ago that tested the functionality and memory of officers who were physically stressed to the point of exhaustion. Click here to read about it.)


Tested in the current study were 64 officers from an urban area of Canada, ranging in age from 22 to 59 and in experience from newly on the street to nearing retirement. They were randomly divided into two groups –Active (“Operational”) Officers and Observer Officers–and then paired with a member of the opposite group. One team at a time, the participants were then immersed in a violent, stress-inducing scenario.

As the action unfolded, the Active Officer, outfitted with a training gun loaded with blanks, was to respond as if experiencing the scenario on duty, while the Observer Officer was simply to passively watch what happened. Among other things, the researchers wanted to see what, if any, differences there would be between accounts of the experience given later by the paired participants.

The experiment involved a multi-stage procedure, which stretched over nearly a week before examination of all pairs was completed.

First, each pair watched a two-minute “briefing video,” purported to be cell phone footage taken in a college classroom. With a class in progress, a disgruntled student enters the room and engages the professor in an argument about poor grades. The perpetrator becomes increasingly agitated, draws a knife from his pocket, and takes the professor and another student hostage, while people flee from the scene.

Then from inside the “classroom,” each officer team, “dispatched” to the location, was exposed to the “experimental scenario,” lasting about four minutes. Standing side by side in designated positions, the officers initially are able to see the suspect threatening his hostages on “live” footage of the “on-going” incident from a closed-circuit TV camera trained on the hallway outside. Within seconds, the suspect bursts into the classroom, using a hostage as a shield and holding a knife to his captive’s neck.

After issuing various demands, he frees the hostage, throws the knife to the ground, and retreats back to the hallway. There, again visible on CCTV, he can be “seen tucking a gun into the waistband of his jeans.”

In a “final live interaction,” Hope writes, the suspect re-enters the classroom “in an agitated manner, goading the officers to shoot him.” At a point where he has turned his back on the officers, he suddenly spins around toward them with his hands moving toward his waistband and then his hands were suddenly thrust forward in a shooting position toward the officers. The gun, however, remains undrawn throughout. The assailant immediately pulled his hands into a hidden posture under his body as he fell.

The scenario ended once the Active Officer responded to this movement.


This scenario, Hope explains, was developed through “extensive discussion with firearms instructors and police trainers” to be realistic and challenging enough to create “a natural physiological stress response” and complex enough that “the participants could be questioned about [it] in detail.”

That the scenario was a successful high stressor was well documented by cardiac monitors. During the scenario, Lewinski told Force Science News, the average Observer Officer’s maximum heart rate doubled, and the Active Officer’s pulse rocketed “significantly higher” yet.

An even “more reliable measure of stress,” he explains, was the fact that the officers’ rapid heart rate sustained consistently over a period of time, indicating the strong influence of stress chemicals. Again, this distinction was significantly more pronounced in Active Officers, who were personally responsible for dealing with the situation, compared to mere Observers.


For about 45 minutes after the scenario ended, the two officers were separated to avoid their discussing the incident. Then, with no imposed time pressure, they independently engaged in a two-part memory test.

  1. In a “free recall” exercise (somewhat mimicking a cognitive-style interview) they were instructed to write down “as much information as they could remember” about the initial video briefing and the main scenario, making their accounts “as complete and accurate as possible” without guessing.
  2. They then were asked to answer an extended list of 94 “closed questions” modeled on the style and content “often adopted by investigators.” A few questions asked for “subjective assessment” of the suspect, such as what his demeanor was. But most of these sought factual information about the briefing and live role-playing that could be verified with contemporaneous digital recordings.

A subset of 14 closed questions was deemed to be of supreme importance. Hope writes: These questions “were identified by legal and police training advisors as critical…with respect to an officer’s understanding of the final stages of the scenario and underpinning any justification to shoot.”

Specifically, these key inquiries focused on determining what the Active Officers and Observers remembered about the perpetrator’s action, his weapon position, and officer response.

On average, Hope reports, the participants took about two hours to complete the recall tasks. The results were carefully evaluated for amount and accuracy of information.


“Our findings showed a dramatic progression of memory impairment about what took place,” Lewinski says, “especially for the Active Officers.”

In freely recalling details about the briefing video, the researchers found on average that there was no significant difference between the amount or accuracy of information remembered by Active and Observer Officers.

However, significant free recall differences arose regarding the action as the officers became personally present in the intense, escalating live experimental scenario. Although the accuracy of what was recalled was essentially the same for both types of participants, Active Officers reported a significantly lower quantity of correct details than Observer Officers, Hope writes. In other words, the ability of Active Officers to describe what happened became sketchier.

In handling the “critical subset” of closed questions, particularly details involving the suspect’s weapon, disparity between the two officer groups became decisively evident. The overall recall of both groups degraded, but Active Officers provided far fewer correct answers and significantly more incorrect answers than Observers regarding the weapon “in the final moments of their interaction,” a particular area of memory “vulnerability,” Hope reports.

The average Active Officer dramatically trailed his Observer partner in accurately answering such questions as:

  • What happened when the culprit turned towards you?
  • Was there a weapon in his hand at this point?
  • If yes, describe how he presented the weapon?
  • Did the culprit discharge a weapon during the incident?
  • What was the position of the culprit’s gun when he was impacted by round(s) from the officer? (Of Active Officers, 85% discharged their weapon during the scenario.)
  • Where was the [suspect’s] gun at the end of the scenario?

One particularly startling finding emerged from the researchers’ tally. Despite spinning and moving his hands in a provocative manner, the suspect kept his gun tucked in his waistband throughout. Yet, Hope writes, roughly 20 percent of the participants–Active Officers and Observers alike–“explicitly reported” that the suspect “pointed a weapon at them/in their direction in the final scene” of the scenario.

She notes: All officers who reported seeing the weapon pointed at them “expressed surprise when told that was not possible.”


Further research is needed to fully explain the phenomenon of seeing a gun that wasn’t there, Hope says. However, it seems likely that “expectation-driven” judgment of the suspect’s movement within a violent setting was involved. Or, to cite a cynical view, perhaps officers reported seeing a pointed gun under pressure to justify their own use of lethal force.

“Deliberate fabrication…lies beyond the scope” of the study, Hope writes. But the findings reveal other important and less controversial realities about “honestly held” memories that should be taken into consideration by investigators of officer-involved shootings and other high-intensity events, Lewinski says.

“Considering that Active and Observer officers stood side by side while exposed to the same threatening scenario yet had some critically different memory qualities tells us a lot about the unique pressures placed on officers who are forced to perform under high-stress conditions, compared to other eyewitnesses,” Lewinski says.

The impairment of Active Officer recall regarding weapon details during the most critical part of the scenario may be attributed to a couple of related factors, the researchers suggest.

  • Active Officers had higher levels of stress throughout the scenario and that stress undoubtedly would have been at its maximum when the threat level seemed greatest. It has been solidly established in scientific literature that the greater the stress, the more likely that memory will be flawed.
  • At the same time, the added cognitive load required by Active Officers to handle their time-pressured tactical and decision-making responsibilities would also have been at its greatest in the rapidly escalating final scene. This combination may have disrupted the ability of those officers to detect and thoroughly process details about the suspect and his weapon.
  • After a real-world shooting, where the stakes obviously are much higher than in a research scenario, “it is reasonable to assume that officers may also experience stress at the reporting stage,” Hope writes, thereby potentially compounding the matter.

In summary, Lewinski states: “This study is added evidence that to expect an officer actively involved in a life-threatening encounter to resolve the action and completely grasp and later accurately describe in detail everything that happened may be expecting too much from the average human being.

“Investigators need to remember that an officer who misses or misstates information about an event that later becomes significant is not necessarily being deceptive or self-serving.”

In the words of the study: In regard to investigative procedures and policies, it is important that the treatment of operational witnesses (Active Officers) be “well-informed [about] the malleability of memory and appreciate the necessity for careful and ethical memory elicitation practices….

“[I]t is critical that practitioners in the legal system, whether lawyers, prosecutors, or judges, are cognizant of the potential for naturally occurring memory errors, gaps, and inconsistencies among all witnesses but particularly operational witnesses, such as armed officers [in] challenging incidents….”

Across several pages in their report, incidentally, the researchers provide a valuable summation of memory findings by other scientists in recent years that help explain why it is “difficult to predict what will be remembered from stressful events.”

At this writing, the date for Law and Human Behavior to publish the study has not been set. We’ll report when the study is available for access in full.

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