The Weapons Priming Effect

"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

There is a theory in social psychology that aggressive behaviors can be stimulated by simply seeing a weapon. I have been skeptical of this effect for a while, as it sounds suspiciously like Bargh-style social priming. The manipulations are very subtle and the outcomes are very strong, and sometimes opposite to the direction one might expect. This is the first of several posts describing my mixed and confused feelings about this priming effect and my ongoing struggle to sate my curiosity.

The original finding

First, let me describe the basic phenomenon. In 1967, two psychologists reported that simply seeing a gun was enough to stimulate aggressive behavior. This suggested a surprising new cause of aggressive behavior, in that simply seeing aggressive primes could provoke aggressive behavior.

In their experiment, Berkowitz and LePage asked participants to perform a task in a room. The design was a 3 (Object) × 2 (Provocation) + 1 design. For the object manipulation, was a piece of sporting equipment in the room. In one condition, the equipment was a rifle and revolver combination; the participant was told the weapons belonged to the other participant. In another condition, the equipment was again the rifle and revolver, but the participant was told the weapons belonged to the previous experimenter. In a third condition, there were no objects on the table.

The provocation manipulation consisted of how many shocks the participant received from the other participant. Participants were provoked by receiving either 1 or 7 electrical shocks.

The extra cell consisted of participants in a room with squash racquets instead of guns. All of these participants were strongly provoked.

So that's 100 participants in a 3 (Object: Confederate's Guns, Experimenter's Guns, Nothing) × 2 (Provocation: Mild, Strong) + 1 (Squash Racquets, Strong Provocation) design. That's about 14 subjects per cell.

The researchers hypothesized that, because shotguns are weapons, they are associated with aggression and violence. Exposure to a shotgun, then, should increase the accessibility of aggressive thoughts. The accessibility of aggressive thoughts, in turn, should increase the likelihood of aggressive behavior.

Berkowitz and LePage found results consistent with their hypothesis. Participants who saw a shotgun (and were later provoked) were more aggressive than participants who saw nothing. They were also more aggressive than participants who had been heavily provoked but seen a squash racquet. These participants gave the confederate more and longer electrical shocks.

Extensions and Public Policy 

I'd been curious about this effect for a long time. I do some aggression research, and my PhD advisor conducted some elaborations on the Berkowitz and LePage study in his early career. But I really grew curious when I listened to Brad Bushman's appearance on Mother Jones' "Inquiring Minds" podcast.

Bushman joined the podcast to talk about the science of gun violence. About the first half of the episode is devoted to the Weapons Priming Effect. Bushman argues that one step to reducing gun violence would be to make guns less visible. For example, guns could be kept in opaque safes rather than in clear display cases. Reducing the opportunities for aggressive-object priming would be expected to reduce aggression and violence in society.

Would you mess with someone who had this in their rear window?

In the podcast, Bushman mentions one of the more bizarre and counterintuitive replications of the weapons priming effect. Turner, Layton, and Simons (1975) report a bizzare experiment in which an experimenter driving a pickup truck loitered at a traffic light. When the light turned green, the experimenter idled for a further 12 seconds, waiting to see if the driver trapped behind would honk. Honking, the researchers argued, would constitute a form of aggressive behavior.

The design was a 3 (Prime) × 2 (Visibility) design. For the Prime factor, the experimenter's truck featured either an empty gun rack (control), a gun rack with a fully-visible .303-caliber military rifle and a bumper sticker with the word "Friend" (Friendly Rifle), or a gun rack with a .303 rifle and a bumper sticker with the word "Vengeance" (Aggressive Rifle). The experimenter driving the pickup was made visible or invisible by the use of a curtain in the rear window.

There were 92 subjects, about 15/cell. The sample is restricted to males driving late-model privately-owned vehicles for some reason.

The authors reasoned that seeing the rifle would prime aggressive thoughts, which would inspire aggressive behavior, leading to more honking. They run five different planned complex contrasts and find that the Rifle/Vengeance combination inspired honking relative to the No Rifle and Rifle/Friend combo, but only when the curtain was closed, F(1, 86) = 5.98, p = .017. That seems like a very suspiciously post-hoc subgroup analysis to me.

A second study in Turner, Layton, and Simons (1975) collects a larger sample of men and women driving vehicles of all years. The design was a 2 (Rifle: present, absent) × 2 (Bumper Sticker: "Vengeance", absent) design with 200 subjects. They divide this further by driver's sex and by a median split on vehicle year. They find that the Rifle/Vengeance condition increased honking relative to the other three, but only among newer-vehicle male drivers, F(1, 129) = 4.03, p = .047. But then they report that the Rifle/Vengeance condition decreased honking among older-vehicle male drivers, F(1, 129) = 5.23, p = .024! No results were found among female drivers.

Overgeneralizing from Turner et al. (1975)
I was surprised to find that the results in Turner et al. (1975) depended so heavily on the analysis of subgroups. In the past, whenever people told me about this experiment, they'd always just mentioned an increase in honking among those who'd seen a rifle.

Take, for example, this piece from Bushman's Psychology Today blog. Reading it, one gets the impression that a significant increase in honking was present across all groups, in contrast to the significant decreases in other subgroups:

The weapons effect occurs outside of the lab too. In one field experiment,[2] a confederate driving a pickup truck purposely remained stalled at a traffic light for 12 seconds to see whether the motorists trapped behind him would honk their horns (the measure of aggression). The truck contained either a .303-calibre military rifle in a gun rack mounted to the rear window, or no rifle. The results showed that motorists were more likely to honk their horns if the confederate was driving a truck with a gun visible in the rear window than if the confederate was driving the same truck but with no gun. What is amazing about this study is that you would have to be pretty stupid to honk your horn at a driver with a military rifle in his truck—if you were thinking, that is! But people were not thinking—they just naturally honked their horns after seeing the gun. The mere presence of a weapon automatically triggered aggression.

On Inquiring Minds, Bushman again acknowledge that the effect is, a priori, implausible. One should think twice before honking at an armed man, after all! In my estimation, counter-intuitive effects should be judged carefully, as they are less likely to be real. But this implausability does not dampen Bushman's enthusiasm for the effect. If anything, it kindles it. 

Next Posts
Naturally, the literature on weapon priming is not limited to these two papers. In subsequent posts, I hope to talk about meta-analyses of the effect. I also hope to talk about the role of science in generating and disseminating knowledge about the effect. But this post is long enough -- let's call it at this for now.