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Research: Detection of firearms by police officers and civilians

Researchers examined the ability of law enforcement officers and civilians to detect objects in the hands of other people

Researchers used Signal Detection Theory to examine the ability of law enforcement officers and civilians to detect objects in the hands of other people.

By Benjamin K. Barton, Ashley Bogar and Casey Kovesdi

Many police officers spend their shifts experiencing relative calm punctuated by brief periods during which decisions must be made quickly, sometimes resulting in use of force. Officers typically make such decisions based on little information and in the context of factors such as poor lighting or physiological overload from stress. However, decisions made when contacting a person who may have a weapon begin simply with the basic perceptual process of detection. For example, determining the dark object in a driver’s hand as they emerge quickly from their vehicle is a wallet or a man on a dark sidewalk pulling an object from his pocket is actually holding a smartphone.

We used Signal Detection Theory to examine the ability of law enforcement officers and civilians to detect objects in the hands of other people. Signal Detection Theory – used widely in the field of human factors – involves a comparison between the actual “state of the world” surrounding an individual and the individual’s response in terms of whether or not a stimulus is present. In our study, stimuli were either a firearm or a “neutral” object such as a cell phone or wallet.


Forty adults participated. Half of the sample comprised individuals from local law enforcement agencies, ranging from 1 to 28 years of experience (average of 11.35 years) and in age from 25 to 56 years. Law enforcement participants were matched by sex (19 men, 1 woman) and age with individuals recruited from the local community. Six of the law enforcement participants had served in the military; two had combat experience. Among all participants, most (97.4 percent) had previous experience with firearms and five of the law enforcement participants were firearms instructors.

Measures and Gun Detection Task

Participants viewed 32 digital photographs of 16 Caucasian males pulling objects from either the front pocket of a hoodie or backpack. Two photos were taken per individual: one with a Smith & Wesson Shield pistol and one with a neutral object (cell phone or wallet). The presence of a pistol or neutral object was balanced, each appearing in 50 percent of the photos.

Each of the 32 photographs was used twice; paired once with a scenario, and once without. The 16 commonly encountered scenarios were developed through discussion with local law enforcement. The scenarios allowed participants to form expectations prior to viewing the stimulus images. Half the scenarios represented “high” expectancy of the presence of a firearm, while the other half represented “low” expectancy.

The high expectancy was: “You are dispatched to a domestic in progress. Dispatch informs you there are firearms in the home. As you approach the residence, this person emerges from the front door...” The low expectancy was: “While on patrol, you are walking through a park and see this person sitting on a picnic table…”

Each scenario was used twice; paired once with a firearm image, and once with a neutral image. The remaining 32 image pairs were presented without a scenario.

The detection task was based on the change blindness paradigm, which allows researchers to test whether someone fails to detect changes in a visual scene. Images were paired with background-only photos to form sets of images. Each trial comprised 800 milliseconds of a background image followed by a 200 milliseconds black masking screen, and finally 1000 milliseconds of the stimulus image. Participants pressed the space bar to begin each trial, then one of two different keys to indicate the presence of a gun or a neutral object. The trial ended after a response was entered or the stimulus image had been displayed for 1000 milliseconds.

We analyzed reaction times and signal detection indicators across the trials. Reaction times were recorded in milliseconds, including a “timeout” if the participant failed to respond within the 1000 milliseconds timeframe. Signal detection indicators were derived from the key presses and included four kinds of responses:

  • Detecting a gun when present (hits);
  • Responding correctly that a gun was not present (correct rejections);
  • Missing a gun when one was present (misses);
  • Responding that a gun was present when one was not in the photo (false alarms).

Key Findings

Several key findings emerged suggesting law enforcement training makes a positive difference in performance.

  • Law enforcement participants demonstrated a trend for faster reaction times than civilians regardless of whether or not they were primed with a scenario.
  • Law enforcement participants were more accurate than civilians when detecting object type (gun or neutral object); 95 percent versus 88 percent.
  • Law enforcement participants performed consistently regardless of the scenario, whereas the performance of non-law enforcement participants varied depending on whether or not they were primed with a scenario and whether the scenario was high or low expectancy.

Results suggest that officers are faster and more accurate than civilians in the detection of objects in the hands of those they contact in the field and perform more consistently regardless of the expectancy of a person holding a weapon. Consistency in performance is important because an officer responding to a call cannot assume the nature of the problem will remain the same on his or her arrival. Unlike a civilian, officers may have little choice in becoming involved in a situation in which their safety is threatened. Not only are officers forced to make difficult decisions frequently and under pressure, our results indicate they are perhaps more likely to do so with greater detection ability and accuracy.

How can our findings inform training?

We believe our findings can be put to practical use in training:

  1. First, our findings suggest patrol experience may allow officers to become faster, more accurate and less bound by the initial scenarios they encounter. Such improvement should happen rapidly during the field training process for new officers.
  2. Training can complement patrol experience (supporting point 1 above). Live-fire range exercises and active shooter training should be structured to allow officers to practice differentiating weapons from other objects and adapt to mismatches between dispatch information and actual information encountered on calls.
  3. Do not forget the importance of verbal skills and command presence. Verbal control during citizen contacts decreases the chance officers will be forced to differentiate between weapons and other objects, stopping the problem before accurate detection even becomes necessary.

About the Authors

Dr. Benjamin Barton is an associate professor in the Department of Psychology and Communication Studies at the University of Idaho. Dr. Barton studies pedestrian safety, quiet vehicle technology, automation, and firearms safety. Dr. Barton also serves as a reserve officer with five years patrol experience.

Ashley Bogar and Casey Kovesdi received their Master’s degrees in Human Factors in the Department of Psychology and Communication Studies at the University of Idaho.