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Methodology and Results


The present study is a compilation of 4 separate experiments conducted with officers of a large police department in the Southwestern United States. The experiments sought to measure the following:


Experiment #1: Reaction time to a visual stimulus

Experiment #2: Time it takes to stop pulling the trigger

Experiment #3: Simple decision-making

Experiment #4: The role of anticipation


A total of 102 police officers were utilized in each of the four experiments. The officers’ participation in the experiments was voluntary.


Experiment #1: Reaction time to a visual stimulus


Experiment #1 involved the use of a stimulus board that was placed in front of each par- ticipating officer. The stimulus board was a 10”x 10” square and displayed a pattern of clusters of light on the face of it. There were 9 clusters of lights on the square board (3 rows containing

3 clusters each) and each cluster contained 3 LED indicators. While viewing the board, officers were asked to grip a modified Glock training pistol. The Glock was fitted with an electronic device to capture trigger-pull data and record it in a computer. Officers were instructed to ob- serve the light clusters in the upper left quadrant of the stimulus board. They were told to pull the trigger one, as quickly as possible, when a particular green light was illuminated.


The average trigger pull reaction for the 102 participating officers, upon viewing the green light, was 0.31 seconds. Broken down further, it took an average of 0.25 seconds to men- tally process that the light was on and decide to pull the trigger; it took 0.06 seconds mechani- cally pull the trigger.


Experiment #2: The Time it takes to Stop Pulling the Trigger


Officers in this phase of the study were instructed that the researcher was measuring the officer’s ability to pull the trigger rapidly. The officer was asked to repeatedly pull the trigger as quickly as possible when the light on the stimulus board came on. However, they were also instructed to stop pulling the trigger immediately upon the light going off. In fact, they were misinformed that any extra trigger pulls after the light stopped illuminating would count against their overall score. As such, this experiment modestly added the elements of on-going attention and motivation.


On average, participating officers stopped pulling the trigger within 0.35 seconds from when the light went off. Approximately 68% of the officers (one standard deviation) fell within the range of 0.10 and 0.60 seconds to cease pulling the trigger. Many officers did pull the trig- ger more than once after the light went off. In one example, an officer pulled the trigger three times during the illumination of the light, began a fourth trigger pull as the light went out, and then pulled the trigger a fifth time. The fourth and fifth trigger pull took only a half second to complete. This officer, reacting within a range that is comprised of 68% of the participants, still had two “unjustified” trigger pulls.


Experiment #3: Simple Decision-Making


Through this experiment, an attempt was made to understand the impact of simple deci- sion-making and visual complexity on reaction time. This experiment was an extension of Ex- periment #1 in that this experiment added confounding elements to the simple determination of whether a light was illuminated (as was the case in Experiment #1). The element of a “go/no- go” decision requirement was one such addition. In Experiment #1, the illumination of the green light in the upper left corner (the only light to be illuminated) was all one needed to pull the trigger. In Experiment #3, officers were instructed that cluster of lights may be illuminated anywhere on the top line of the board. Further, they were only to pull the trigger when all three lights in a cluster were illuminated. They were not to pull the trigger if only two lights of a cluster came on.


The requirement of go/no-go decision-making in this experiment essentially doubled the reaction times found observed in Experiment #1. This is consistent with other reaction time literature. The average for the 102 participating officers to identify the illumination of 3-light clusters, react to it, and actually pull the trigger was 0.56 seconds. If you back out the 0.06 sec- onds to mechanically pull the trigger, then the average time to perceive the light cluster, men- tally process it, and decide to pull the trigger was 0.50 seconds (as compared to 0.25 seconds in Experiment #1).


The range of reaction times (not counting the actual trigger pull) was 0.44 seconds to 0.69 seconds within one standard deviation (68% of the officers). The 25% variability with one standard deviation can be explained in part by individual reaction and processing ability, vary- ing capacity to concentrate, anxiety, and other factors. It is worth noting that these same vari- ables exist amongst the same officers in the real world. An obvious implication is that average, comparable officers do not necessarily bring the same baggage or ability to a shooting incident; different officers may bring about different outcomes to otherwise similar circumstances.


An interesting side note of Experiment #3 relates to the so-called “Oops Factor.” Of all trigger pulls, 9% occurred when the cluster pattern did not warrant them. Further, 4% of the 3- light cluster illuminations resulted in no trigger pull when there should have been one. While the error rates here are not unfamiliar or even alarming within the context of laboratory experi- ments, the outside world (including prosecutors, community leaders, academicians, and victims of accidental shootings) are less forgiving of honest errors made in the field.


Experiment #4: The Role of Anticipation


The final experiment of the study measured the influence of anticipation on reaction times. In this experiment, the participants were presented with a variety of lights on the stimu- lus board. All of the lights illuminated at irregular intervals. The lights, which were yellow, red, and green, would go on and off. Eventually, a pattern of green lights would begin to ap- pear. When the pattern of green lights was complete, the participant was expected to pull the trigger. If the pattern never became complete, then no trigger was warranted and the participant was to wait for the next completed pattern.


Like Experiment #3, this phase of the study required officers to make a “go/no-go” deci- sion. Further, Experiment #4 included greater visual complexity than any of the other three experiments. However, the anticipation of the perceived “threat” in the form of an increasingly- complete green light pattern was an entirely new dimension embedded in the officers’ reactions.


Interestingly, the addition of an ability (or liability) to anticipate the threat caused the reaction times of participants to drop from 0.56 seconds to 0.46 seconds. Further, anticipation was apparently responsible for reducing the failure to pull the trigger when justified to practi- cally zero. Perhaps somewhat surprising, the element of anticipation also appears to have re- duced unwarranted trigger pulls. While some observers might have expected that anticipation would cause officers to “jump the gun,” in fact, just the opposite occurred. The unwarranted trigger pull rate dropped from 9% in Experiment #3 to 5% in Experiment #4. Quite possibly, the greater level of concentration devoted to the forming pattern of green lights made it more keenly evident to participants when the pattern failed to ultimately materialize, thereby reducing the number of improper trigger pulls.


The table below summarizes the reaction times measured in the four experiments.




While all four experiments in this study were conducted under laboratory conditions, the implications for police officers on the streets are fairly evident. It does not take a significant degree of imagination to see how variability in officer reaction times under different conditions, as measured by the consummation of trigger pulls, is relevant for assessing police shootings in the field.


As noted earlier, a number of studies have shown that armed suspects can fire upon po- lice officers and begin to run away before the officers can physiologically react and return fire (20, 21-23). The 4-part study presented here provides additional empirical evidence concerning the limited capacity of police officers, or any other human beings, to react. Stated simply, reaction takes time; further, reaction is difficult to turn off. “Stopping” is a reaction to a change in stimulus. Like any other reaction, “stopping” is never instantaneous.


While some elements in the community and academe will forever remain skeptical of officers who are involved in a shootings, police investigators and prosecutors should give careful consideration to the findings of this study and others related to it. If an officer with an otherwise exemplary record is involved in a shooting incident, and, despite the officer’s insistence that a threat was perceived, the suspect was shot in the side or back, investigators and prosecutors may want to consider that something other than an execution or attempted execution took place.


In fact, the physical and psychological limitations of the human condition do not apply only to law enforcement officers. Detectives called to the scene of a “routine” shooting inci- dent between two civilians may wish to not-so-readily dismiss the claim of the suspect that the victim had posed a threat, despite entry bullet wounds in the victim’s back. Obviously, consideration of reaction time doesn’t explain all shootings. Common sense, eye-witness testimony, and physical evidence tend to close the cases. But in those instances when common sense suggests the suspect’s innocence while the victim’s wounds suggest the suspect’s guilt, innocence may still be an option.


There are also implications in this study for academe. In particular, more scholarly research should be done on past and potential use-of-force encounters which are suspicious in nature to determine what role human capacity—and especially mental chronometry—play in these incidents. Once again, reaction times do not explain all use-of-force encounters. Further, the existence of some unlawful use-of-force in the law enforcement community, past and present, is well documented and must be confronted and condemned. However, use-of-force decisions and outcomes which appear unjustified but are actually manifestations of limited human capac- ity are not unlawful (although they may be mistakes and they may be tragic). Through additional studies, the academic community can not only educate itself in this area, but serve as a genuine partner with law enforcement to develop realistic and useful training and policies that will minimize, where possible, tragic use-of-force and deadly force encounters while still promoting the safety of the officers.


Police officers cannot be expected to defy biological and physical laws as they perform their duties. To require perfect comprehension and instantaneous, flawless reaction of police officers in the field is to require the impossible. And to send officers to prison when they fail to do the impossible is a most grievous injustice. Only through deference to scientific research which uncovers the true capacity (or incapacity as the case may be) of police officers to react to threatening stimuli may we begin to understand how at least some of the deadly force encounters play out between law enforcement and suspects. Certainly it is our obligation as constitu- ents of the criminal justice system to follow truth wherever the science takes us.




1. Auten, J. (1976). The paramilitary model of police and police professionalism. In Bloomberg, A.S. and Niederhoofer, E. The Ambivalent Force: Perspectives on the Po lice, New York, NY: CBS.


2. Brown, A. (1981). The future of policing in Canada. In McGrath, W.T. (Ed.), The Police Function in Canada, Toronto: Methuen.


3. Klockers, C. and Matrofski, S. (1991). Thinking About Police: Contemporary Readings, New York, NY: McGraw-Hill.


4. Hodgson, J.F. (2001). Police violence in Canada and the USA: Analysis and manage ment. Policing: An International Journal of Police Strategies & Management, 24(4), 520-549.


5. Blumberg, M. (2001). Controlling police use of deadly force: Assessing two decades of progress. In Dunham, R.G. and Alpert, G.P. (Eds.), Critical Issues in Policing. Prospect Heights, IL: Waveland Press.


6. Alpert, G.P. and MacDonald, J. (2001). Police use of force: An analysis of organizational characteristics. Justice Quarterly, Vol. 18, 393-409.


7. White, M. (2000). Assessing the impact of administrative policy on use of deadly force by on- and off-duty police. Evaluation Review. 24(3), 295-318.


8. Smith, B.W. (2004). Structural and organizational predictors of homicide by police. Policing: An International Journal of Police Strategies & Management. 27(4), 539- 557.


9. Liska, A. and Yu, J. (1992). Specifying and testing the threat hypothesis. In Liska, A. (Ed.), Social Threat and Social Control. Albany, NY: SUNY Press.


10. Rhodes, C. (1969). Authority in a Changing Society. London: Anchor Press.


11. Sennett, R. (1981). Authority. New York, NY: Random House.


12. Penner, L.A. (1986). Social Psychology Concepts and Applications. St. Paul, MN: West Publishing.


13. Fyfe, J. (1996). Training to reduce police violence. In Geller, W.A. and Toch, H. (Eds.), Police Violence: Understanding and Controlling Police Abuse of Force. New Haven, CT: Yale University Press.


14. Alpert, G.P. and Smith M.R. (1999). Police use-of-force data: Where we are and where we should be going. Police Quarterly, 2(1), 57-78.


15. Perera, T.B. and Haupt, E.J. Museum of the history of reaction time research. Mon claire State University, NJ. Retrieved from psychology/ museum/mrt.html.


16. Donders, F.C. (1968). On the speed of mental processes. In W. G. Koster (Ed.), Attention and performance II. Acta Psychologica, 30, 412-431. (Original work published in 1868).


17. Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4, 11–26


18. Schmidt. R.A. and Wrisberg, C.A. (2000). Motor Learning and Performance (2nd ed.). Champaign, IL: Human Kinetics.


19. Smith, G. (1990). Evaluation of law enforcement officer combat handgun skills. Smith and Wesson Academy Newsletter, November, 7-8.


20. Tobin, E.J. and Fackler, M.L. (1997). Officer reaction-response times in firing a hand gun. Wound Ballistics Review: Journal of the International Wound Ballistics Association, 3(1), 6-9.


21. Lewinski, B. and Grossi, D. (1999). The suspect is shot in the back: Is your shooting clean? The Police Marksman. September/October, 22-24.


22. Lewinski, B. (2000). Why is the suspect shot in the back? The Police Marksman. No vember/December, 20-28.


23. Lewinski, B. (2002). Stress reactions related to lethal force encounters. The Police Marksman. May/June, 23-28.


24. Weeg, J. (2002). What you need to tell the prosecutor in your next use-of-force case. The Police Marksman. May/June, 45-47.


25. Remsberg, C. (2004). Telling the truth about police shootings. The Police Marksman. November/December, 18-22.