Thesis (M.S., Psychology) -- University of Idaho, 2015 | Research examining use of firearms by law enforcement has largely focused on issues such as racial bias or conditions of cognitive load or stress. The present study takes a more foundational approach by examining use of firearms as a problem of basic perception. Detection of firearms was examined within the framework of environmental factors and contextual influences, and compared performance between participants with and without law enforcement training. The sample comprised twenty law enforcement officers and twenty individuals drawn from the local community. Each participant completed a firearm detection task, during which reaction times and signal detection indices were recorded. Slower reaction times and greater overall accuracy of detection was predicted among participants with law enforcement training. Results suggest a pattern of greater detection accuracy by law enforcement participants, as well as expand the understanding of factors underlying the decision-making process involved in the use of deadly force.