Why so many shots fired? Understanding police officer reaction time to stop shooting

What some civilians and LE critics perceive as an act of reckless disregard for life, is often merely the product of physiology – specifically, reaction time


By Jason Helfer

Following an officer-involved shooting (OIS), one of the first questions that arises is why an officer fired the number of rounds they did. Relatives, reporters and law enforcement critics question why officers fired so many rounds, why suspects were shot after already falling to the ground, or why suspects were shot in the back.

For example, in the shooting of Stephon Clark in Sacramento, two officers fired 20 rounds – a number that was repeated in media reports, along with a quote from his grandmother: “They didn’t have to shoot him that many times.” The fact that some of the bullets that hit Clark entered his back was also used to argue that officers were using excessive force on a person who did not represent a threat. (Although an autopsy conducted by Clark’s family concluded he was shot eight times, with most of the bullets entering his back, an autopsy conducted by the Sacramento County coroner later concluded Clark was shot seven times, with three of the shots hitting him in the back.)

Understanding reaction time and perception-reaction time is critical when developing and implementing training programs to improve officer performance and enhance safety. (Photo/PoliceOne)
Understanding reaction time and perception-reaction time is critical when developing and implementing training programs to improve officer performance and enhance safety. (Photo/PoliceOne)

It’s understandable that civilians who read reports of officers firing multiple, sometimes dozens, of rounds at a suspect will question whether the officers used excessive force. Law enforcement is always under a proverbial societal microscope, even more so in this post-Ferguson era.

In truth, however, what some civilians and law enforcement critics perceive as an act of reckless disregard for life, or even intentional murder, is often merely the product of physiology – specifically, reaction time.

In a perfect world, officers would stop shooting as soon as the threat has been mitigated. If we think about this for even a few minutes, however, we can see why a real-world OIS is far from perfect.

Attentional Capacity Is Limited

To stop shooting, the officer must first perceive the cessation of a threat before they can react to stop the action initiated to combat the initially perceived threat. While in hindsight there may be clues – the suspect’s hands going up, a bystander yelling, “He’s unarmed,” or the suspect falling to the ground – during the incident, the officer’s attentional load is taxed, which in turn affects his capacity to perceive.

Attentional capacity is a finite resource in all humans, one that is allocated according to need. Marc Green, PhD, an expert in perception, attention, reaction time and memory, describes attention like a bucket of water: Every cup or spoonful from the bucket leaves less water (attention) for other purposes. Paying attention to one type of sensory input (auditory, visual, etc.) can impair attention to another, such as actions indicating the cessation of the threat that prompted an officer to shoot.

Researchers at Johns Hopkins University ran a series of tests that illustrate this phenomenon. The researchers examined human brain activity during attention shifts between seeing and hearing. Shifting from seeing to hearing caused decreased activity in the visual cortex, and vice versa. Retired Army officer and firearms expert Eric Lamberson notes this research supports the conclusion that a person paying attention to auditory stimuli such as a radio or cellphone could have diminished visual performance. An officer could appear to be looking right at something but may not notice it or process and act upon it.

Now try to picture a police radio broadcasting, sirens wailing, lights flashing, and civilians and/or other officers yelling while an officer is trying to observe a subject. And let’s not forget the officer is in a high-stress situation, one in which a split-second decision could mean life or death for an involved party. Is it not possible a visual cue that tends to indicate a cessation of a threat could be inadvertently missed?

Other real-life factors also come into play. Dr. William Lewinski, founder and director of the Force Science Institute, notes that a person’s perception is dependent on “the direction and quality of the senses of the perceiver, and this varies on an individual level due to nutrition, fatigue, experience, interest, etc. of the observer.” A police officer who’s worked 8 hours and experienced several stressful calls prior to the OIS may struggle more with processing multiple stimuli than an officer who’s not fatigued or stressed before the incident.

Perception-Reaction Time

Second, the officer must translate the perception that a threat has been mitigated into action. The combined time for a person to perceive a threat and react to it is known as the perception-reaction time. It is, of course, longer than reaction time alone, and generally ranges from .7 seconds to 1.5 seconds.

Experiments conducted by Force Science Institute involving 102 experienced law enforcement officers showed that when responding to a simple stimulus in laboratory conditions, some officers were able to stop shooting immediately, but the slowest to stop completed six more trigger pulls. In a report summarizing the research, Force Science Institute noted, “If an officer were to take [merely] 0.56 seconds to react to a stop-shooting signal, three to four [extra] rounds could be fired by the officer as an automatic sequence after the signal to stop had already occurred … The slower an officer’s reaction time, the greater number of shots [can] be fired before a conscious stopping can occur.”

Some officers were able to react seemingly instantaneously, resulting in no additional rounds while others took up to 1.5 seconds to cease pulling the trigger, resulting in additional rounds being fired. Why is that? As noted above, a multitude of factors come into play, including the other stimuli coming at the officer and the officer’s physical and mental state. Training plays a role too; just as we can get faster at drawing our weapon, we can get faster at responding to a stop stimulus – at least under controlled conditions.

In sum, the speed in which an involved officer recognizes a “stop stimulus” is directly related to how quickly they can sort through the sea of stimuli during a lethal encounter and pay attention to the stop stimulus. Then, and only then, can an officer process the stop stimulus, decide to cease an action, and initiate a motor response (physical movement) to stop an action.

Now let’s consider gunshots to the back in the context of this discussion. It is entirely possible an officer perceives the subject as a threat when the subject is facing the officer – and that by the time the reactionary trigger pull occurs, the subject is facing away. It is also entirely possible an officer can not stop an already-initiated action sequence quickly enough upon perceiving an action indicative of threat cessation (e.g., the subject turning away).

A Final Word

As I’ve argued elsewhere, human beings are not robots. A job title, training or experience does not make a police officer better able to simultaneously pay attention to, and process, sensory input than a civilian. Thoroughly and impartially analyzing an officer’s performance requires an understanding of the elements of an officer’s response to a start/stop stimulus and associated times, considering perception, decision-making and subsequent motor (physical action) responses. The analysis must also consider the effect of the environment and the officer’s physical and emotional states.

Understanding reaction time and perception-reaction time is critical when developing and implementing training programs to improve officer performance and enhance safety. It is also essential that officers and law enforcement leaders are armed with an understanding of the human body’s finite attentional resources and subsequent physiological responses. Only then can we refute critics armed with the benefit of hindsight and blissful ignorance of the dynamic, stress-invoking and life-changing events associated with law enforcement.


About the author

Jason Helfer is a graduate of the FBI National Academy and has been a law enforcement officer for over 17 years. He has served in various roles for his department, including road patrol, crime scene processing, community services and internal affairs. Jason currently works part time for Lexipol as a Professional Services Representative and recently successfully completed the Advanced Force Science Specialist class offered by the Force Science Institute.

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