Adam T. Biggs, Kyle A. Pettijohn, and Sarah Sherwood published a study titled “How Speed Impacts Threat Assessment in Lethal Force Decisions” in Applied Ergonomics in 2023. In this text, we summarize the key aspects of the article.
The term “lethal force decision” is misleading, often involving rapid, instinctive responses rather than conscious choices. In military and law enforcement, decisions happen within milliseconds due to the urgency of the situations. The study explored how quick decision-making affects threat assessments in these scenarios, considering the well-known speed/accuracy trade-off in cognitive science. This balance between speed and accuracy is critical in lethal force situations.
The study investigated how speed influences decision-making by having participants respond quickly (speeded condition) or at a more relaxed pace (unspeeded condition). The specific conditions were tailored to individual response speeds, accounting for differences explained in the Methods section. Participants encountered various images, some clearly threatening, some clearly non-threatening, and some genuinely ambiguous because the handheld object was not visible. This design encouraged subjective threat assessments, with individuals determining what they perceived as a threat rather than applying predefined rules of engagement.
Speeded responses could impact decision-making in several ways. Behavioral outcomes might reveal changes in the tendency to view stimuli as threatening, quicker information processing under speeded conditions, or alterations in decision thresholds. Of particular interest were the truly ambiguous stimuli. Speeded conditions might incline individuals to perceive a stimulus as threatening, even if they wouldn’t perceive it as such under unspeeded conditions.
To gain a comprehensive understanding, behavioral responses were complemented by decision parameters determined through DDM (Drift-Diffusion Model) calculations. Speed/accuracy trade-offs could affect the decision threshold by reducing the amount of information used for threat assessment, speeding up motor responses (non-decisional factors), increasing information processing speed, altering decision bias, or a combination of these factors. Together, behavioral responses could reveal higher commission error rates in the speeded condition, while DDM calculations could provide insight into what aspects of the decision process changed to cause this increase in errors.
The experiment used photorealistic targets depicting five positions, ranging from least threatening (“both hands up unarmed”) to most threatening (“weapon drawn and pointed”). These positions were repeated 15 times in both speeded and unspeeded conditions, creating 300 trials.
Participants were instructed to respond quickly in the speeded condition and take more time in the unspeeded condition. Time limits were set based on individual response times from practice trials. The order of conditions was counterbalanced.
Each trial began with a fixation cross, followed by a threat image. Participants pressed “z” for non-threat or “m” for threat. Trials not completed within the time limit were excluded. The study explored subjective threat assessment without specific threat criteria or engagement rules.
"Speed/accuracy trade-offs can impact a wide variety of behavioral outcomes, and the evidence presented here demonstrated how speeded conditions could impact decisions in the context of a threat assessment. Speeding the judgment lowered the threshold for information to make a decision and reduced non-decisional factors leading to the outcome. Behaviorally, participants became predisposed to errors of commission for non-threatening targets while also minimizing the window an individual has to make a response. Unfortunately, the trade-off is also almost unavoidable as lethal force scenarios have some of the most urgent need to make an accurate decision under some of the greatest speed pressures which exist. This inevitable combination requires more evidence to explore the influence of speed/accuracy trade-offs in lethal force encounters as well as possible solutions that might reduce the likelihood of errors, such as cognitive training to enhance inhibitory control."
Adam T. Biggs, Kyle A. Pettijohn, Sarah Sherwood, How speed impacts threat assessment in lethal force decisions, Applied Ergonomics, Volume 106, 2023, 103890, ISSN 0003-6870, https://doi.org/10.1016/j.apergo.2022.103890.