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The "Weapons Effect"

Research shows that the mere presence of weapons may increase aggression.

“Guns not only permit violence, they can stimulate it as well. The finger pulls the trigger, but the trigger may also be pulling the finger.”

—Leonard Berkowitz, Emeritus Professor of Psychology, University of Wisconsin

In 1967, Leonard Berkowitz and Anthony LePage conducted a fascinating study.[1] First, participants were angered by a person pretending to be another participant (called a confederate). Next, participants were seated at a table that had a shotgun and a revolver on it—or, in the control condition, badminton racquets and shuttlecocks. The items on the table were described as part of another experiment that the researcher had supposedly forgotten to put away. The participant was supposed to decide what level of electric shock to deliver to the confederate who had angered them, and the electric shocks were used to measure aggression. The experimenter told participants to ignore the items on the table, but apparently they could not. Participants who saw the guns were more aggressive than were participants who saw the sports items. This effect was dubbed the “weapons effect.”

Research also shows that drivers with guns in their cars more likely to drive aggressively.[2] A nationally representative sample of over 2,000 American drivers found that those who had a gun in the car were significantly more likely to make obscene gestures at other motorists (23% vs. 16%), aggressively follow another vehicle too closely (14% vs. 8%), or both (6.3% vs. 2.8%), even after controlling for many other factors related to aggressive driving (e.g., gender, age, urbanization, census region, driving frequency). Recent research replicated this finding in a driving simulation experiment.[3]

Human beings can identify potentially dangerous, threatening stimuli such as spiders and snakes very quickly. This makes sense from an evolutionary perspective because some spiders and snakes are poisonous, and our ancient ancestors who could identify them quickly were more likely to avoid them and live to pass on their genes. Recent research shows that people can identify guns as quickly as they can identify spiders and snakes.[4],[5],[6] These findings are very interesting because guns are modern threats so this cannot be explained as easily using evolutionary principles. Yet guns are far more dangerous to people today than spiders or snakes. Poisonous spiders (e.g., Black Widows, Brown Recluses) kill about six Americans each year.[7] Poisonous snakes (e.g., rattlesnakes) kill about five Americans each year.[8] In comparison, guns kill about 31,000 Americans each year.[9]

Several studies have replicated the weapons effect. A review of 56 published studies reported that the mere sight of weapons increases aggression in both angry and nonangry individuals.[10] A more recent meta-analysis of a larger sample of 151 effect-size estimates from 78 independent studies involving 7,668 participants found strong support for the idea that weapons increase the accessibility of aggressive thoughts and hostile appraisals.[11] However, more research is needed on the link between exposure to weapons and aggression in provoked participants, especially in field settings. A large (N = 678) recent field study found that the presence of a TASER significantly increased physical assaults against police officers.[12] Perhaps the weapons effect occurs because weapons are closely linked to aggression in our brains.

Note. This blog post is based on the following article: Bushman, B. J.(2013). The weapons effect. JAMA Pediatrics, 167(12), 1094-1095. DOI:10.1001/jamapediatrics.2013.3824


[1] Berkowitz, L., & LePage, A. (1967). Weapons as aggression-eliciting stimuli. Journal of Personality and Social Psychology, 7, 202–207.

[2] Hemenway, D., Vriniotis, M., & Miller, M. (2006). Is an armed society a polite society? Guns and road rage. Accident Analysis and Prevention, 38(4), 687–695.

[3] Bushman, B. J., Kerwin, T., Whitlock, T., & Weisenberger, J. M.(2017). The weapons effect on wheels: Motorists drive more aggressively when there is a gun in the vehicle. Journal of Experimental Social Psychology, 73, 82-85. DOI: 10.1016/j.jesp.2017.06.007

[4] Blanchette, I. (2006). Snakes, spiders, guns, and syringes: How specific are evolutionary constraints on the detection of threatening stimuli? The Quarterly Journal of Experimental Psychology, 59(8), 1484–1504.

[5] Carlson, J. M., Fee, A. L., & Reinke, K. S. (2009). Backward masked snakes and guns modulate spatial attention. Evolutionary Psychology, 7(4), 534–544.

[6] Fox, E., Griggs, L., & Mouchlianitis, E. (2007). The detection of fear-relevant stimuli: Are guns noticed as quickly as snakes? Emotion, 7(4), 691–696.




[10] Carlson, M., Marcus-Newhall, A., & Miller, N. (1990). Effects of situational aggression cues: A quantitative review. Journal of Personality and Social Psychology, 58, 622–633.

[11] Benjamin, A. J., Jr., Kepes, S., & Bushman, B. J. (2018). Effects of weapons on aggressive thoughts, angry feelings, hostile appraisals, and aggressive behavior: A meta-analytic review of the weapons effect literature. Personality and Social Psychology Review, 22(4), 347-377. DOI: 10.1177/1088868317725419

[12] Ariel, B., Lawes, D., Weinborn, C., Henry, R. Chen, K., & Sabo, H. B. (2019). The “less-than-lethal weapons effect”: Introducing tasers to routine police operations in England and Wales. Criminal Justice and Behavior, 46(2), 280–300. DOI: 10.1177/0093854818812918

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