Study Of Cops’ Stress Reactions To Deadly Simulator Scenarios

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Based on findings from a new stress study, a research team is recommending, among other things, that investigators of officer-involved shootings should be trained with deadly force simulator scenarios.

“That experience would help investigators better understand the human factors that can come into play when officers face a life-threatening situation,” the lead researcher, Dr. Darrell Ross, told Force Science News.

Many of those factors, including important memory and perception issues, were vividly confirmed in what is said to be the first study of the effects of stress generated by a training simulator.

The research is reported in the journal Law Enforcement Executive Forum in a summary authored by Ross, a CJ professor at Valdosta (GA) State University and a prominent law enforcement consultant and expert witness; former Kansas police major Randall Murphy, a crime scene investigation specialist and director of advanced immersion technologies for the simulator manufacturer Meggitt Training Systems; and Dr. Michael Hazlett, professor emeritus at Western Illinois University’s School of Law Enforcement and Justice Administration.

Their research project, funded by Meggitt Defense Systems, was originally conceived to test whether firearms simulators really are effective in spiking an officer’s stress level to a point suggestive of a real-life lethal encounter, Ross explains.

Not only was that question emphatically answered, Ross says, but an abundance of other results were gathered about the impact of stress that underscore findings by other researchers (including the Force Science Institute) and have important implications for police training.

“There is no doubt this is an important and worthwhile study,” Dr. Bill Lewinski, Executive Director of the Force Science Institute, told FSN. “The researchers made some creative and apparently effective efforts to replicate the type of stress level officers encounter in a real-world shooting situation. Because of this, we need to emphasize that other research conducted on simulators did not find the same results this research team found using Scenarios Two and Three.

“The majority of findings using simulators are similar to that found in this research while using Scenario One,” Lewinski continued. “In that scenario, which appears to be a classic simulator scenario, the officers reported little stress response and researchers noted little actual psycho-physiological reactions, with the exception of memory issues which occurred because of the speed of the unfolding event.

“As these researchers noted, Scenario One was of very brief duration and unfolded quickly. Scenarios Two and Three were quite extended and involved creative efforts to induce time compression where the officers had to do a lot in a very brief time frame, as well as adding a believable perception of high threat and visual and cognitive complexity to the scenario.

“If a simulator is to be used as a stress inducer or inoculator, the trainer needs to also add the elements this team did, or something similar, to the scenarios.”


The study’s research pool consisted of 150 LEOs, primarily from eight medium-sized police and sheriff’s departments in the Tampa, FL, area. Their average age was 37, 80% were male, 75% were Caucasian, nearly 90% had at least some college education, and they ranged from three to 20 years of law enforcement experience. Only about 1/3 had been exposed to any simulator training within three years of the experiment.

To establish pre-test baselines, certain physiological information was gathered from each, including resting heart rate, blood pressure, and saliva samples (to measure the concentration of major stress-related hormones). Then the volunteers were outfitted with “tracking glasses” to monitor eye movement and with a wireless harness device to yield continuous feedback on respiration rate, skin temperature, heart rate, and other physiological data.

Thus wired, dressed in full uniform, equipped with radios for real-time communication, and armed with a Glock simulator pistol, the volunteers were randomly assigned to one of three lethal-force scenarios based on actual field events. One at a time they were exposed to their designated film in a new stress-induction, simulator testing lab.


The different scenarios the three groups encountered varied in complexity and intensity.

Group 1’s two-minute simulation involved a traffic stop on a motorcycle, in which the driver dismounts, makes verbal challenges, then suddenly reaches to a hiding place on his bike, draws a firearm, and shoots at the officer.

Group 2’s call was to a scene of workplace violence, with action extending across about five minutes. Included were a building search, fleeting glimpses of the suspect, encounters with innocent employees, the discovery of a bleeding victim, an assault on a female, a foot pursuit, the attempted hijacking of a vehicle, the arrival of backup officers, the risk of friendly fire, and hostile shots from the offender.

The same scenario was used for Group 3, but the researchers added a live “infusion of high-intensity stressors.” This included pelting the tested officers with “shoot-back” pellets to simulate incoming rounds, shooting them with distracting blasts of air, throwing a phone book at them as if by a rattled employee, flooding the room with extremely bright light to mimic moving outdoors, adding honking horns and other street noise, and imposing the gradually increasing sound of a beating heart throughout the episode.


Each officer again gave saliva samples at 10 and 30 minutes after completing his/her assigned scenario. Then the officers completed a two-part questionnaire to “examine the perceptions and misperceptions” of their simulator experience.

One part asked the officers their subjective impression of the stress they’d experienced. For example, did they feel threatened or fearful; did they sense an increased heart rate, breathing difficulty, visual or auditory distortion; did the action make their thinking difficult; were they aware of perceptual distortions; did they feel “able to cope” with the situation, and so on. The officers were to self-assess 14 variables in all.

Part 2 addressed objectively the impact of stress on perception and memory. In a multiple-choice format, the officers were asked to recall and select details about several dozen “clearly present” specifics related to the circumstances of their scenario, the surrounding environment, characteristics and actions of the suspect, and particulars related to time, sound, and visual elements.

After 48 hours, the officers completed the same questionnaire again at home and submitted it back to the research team.


Although a simulator exercise obviously does not carry the actual life-or-death threat of a real-world encounter, that significant stress was induced and affected the participants was unmistakable, the study team reports. Among the evidence:

  • Analysis of the officers’ saliva for acute stress-related biomarkers revealed “elevation in the stress response” from each scenario, with the subjects in Groups 2 and 3 showing the most significant reaction. Results correlated with the officers’ personal perception of stress and did not vary by gender or ethnicity. The pronounced evidence of elevated stress indicators even in the most experienced officers suggests that basic hormonal reactions do not abate with years of service.
  • Despite the varying stressfulness of the scenarios, a sizeable portion found each encounter “demanding,” ranging from 24% in Group 1 to 66% in Group 3. Still, at least 94% of officers in each group reported they were “able to cope” with the situation presented. (Although failure to cope was not analyzed as part of this study, Ross says that some officers did freeze up, did not respond with their firearm to deadly threats, or became “moderately hysterical” at some points, just as officers sometimes do on the street.)
  • The participants’ personal perceptions of their stress reactions differed among the scenarios. “The scenario’s intensity and duration mattered a great deal,” Ross says. Only 13% in Group 1 reported an increased heart rate, compared to 58% in Group 2 and 68% in Group 3. Perceived breathing difficulties went from 10% in Group 1 to 23% in Group 3. A feeling of fear roughly doubled between Group 1 (22%) and Group 3 (40%), as did the sense of threat (from 34% to 71%).
  • A minority, ranging from 10% to 18% depending on the scenario, reported being aware of visual and/or auditory distortions. Also in the minority (12% to 14%) were those who thought their thinking was negatively affected. The researchers write: “Officers with less than five years of street-level experience were more likely to experience perception distortions.”
  • What the study terms “misperceptions” were commonplace. These included elements of the scenarios that the officers missed seeing and/or failed to recall accurately. Again, such errors of perception worsened as scenario intensity increased. In Group 1, 27% of officers recorded errors in their after-action test; in Group 2, 30%; Group 3, 32%.
  • Besides errors in estimating time and in describing the suspect, the researchers report that frequent misperceptions in the more intense scenarios included “the actual number of persons encountered…, failing to observe blood on the floor…, difficulty recalling statements made by occupants in the building, difficulty in recalling the position from which the subject pointed the weapon,…perception that the subject fired his gun in the building when he actually fired outside, and failure to note that they had fired at the subject with a backup officer standing directly behind the subject.”
  • Even among officers experiencing what was seen as the least intense scenario (Group 1), over 60% of those recording misperceptions incorrectly described the suspect’s clothes, 65% made errors about his verbal threats, and roughly 70% to 80% misstated his weaponry and shots fired.
  • With misperceptions, there was “no significant difference between gender and race.” However, officers under age 30 and over 50, those with less than five years’ street experience, and those who had never before received any simulator training showed the most “significant deterioration in their perception of the scenario events” as the intensity increased.
  • An especially important finding: When the researchers analyzed the questionnaires the participants submitted 48 hours after the simulator tests, they discovered that the officers’ recall had improved by about 20% in all three groups.


Based on these and other results, the study team offers these conclusions:

  1. “In a time in which realistic police training is advocated by educators, police practitioners…and the courts…, the use of a virtual lethal force simulator can indeed produce stressors replicating field encounters…. [S]imulator training should be offered frequently” and “should incorporate intense stressors” to help officers key in on “subject behaviors, pre-assault cues, threat cues, and actual threats.”
  2. The faster a situation unfolds, “the more likely the officer may form misperception[s] of the events. In some cases the officer may not see the action at all.” The suspect on the biker stop, for instance, moved so fast to access his hidden weapon “that many [officers] missed observing the firearm shot at them.”
  3. Likewise, some officers under stress may become so narrowly focused on compelling primary tasks, like apprehending the dangerous suspect, that they develop “inattentional blindness” regarding other actions, people, and objects in the environment, including failing to see a fellow officer in their line of fire.
  4. “After a traumatic event or life-threatening situation, it can be expected that detailed recall of the encounter may be fragmented…. [I]t should not be automatically inferred that an officer is lying or purposely being evasive in an investigation.”
  5. “Errors will never be totally eliminated,” but consistent with the study’s findings, “officers should be allowed to provide a short preliminary public safety statement of the incident to a supervisor, and then be provided with one to two sleep cycles prior to performing further interviews.” Allowing 24 to 48 hours of rest “can enhance… recall of more details…and improve an…investigation.”
  6. “[P]olicymakers should consider adopting the practice of allowing officers to view dash-cam videos of taped incidents [and] to walk through the environment where the shooting occurred.” This can “assist in improving recall and reducing ambiguity” by stimulating visual, auditory, and other sensory triggers of memory.
  7. OIS investigators “should have a fundamental understanding of…the formation of perceptions under stress, individual responses to it, field performance, and recall of traumatic events.” Investigators “should be trained in virtual simulators like other agency personnel to experience…how their body functions under stress.”


Each officer’s performance in the study was videotaped so that further analysis can be made. In all, Ross says, “1,900 variables were generated during the experiment.” This provides invaluable reference material for new studies already underway regarding memory, decision-making, and stress physiology, he says.

The full 20-pg. report of the study can be found with: Ross, D. L., Murphy, R. L., & Hazlett, M. H. (2012). Analyzing perceptions and misperceptions of police officers in lethal force virtual simulator scenarios. In Law Enforcement Executive Forum (Vol. 12, No. 3, pp. 53-73).

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