Sunday, December 9, 2018

Rethinking Turner, Layton, and Simons (1975)

Let's revisit what is a frequently cited set of field experiments purporting to support the notion that the mere presence of a weapon influences aggressive behavior:
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.

The above description could come from practically any social psychology textbook describing the weapons effect, and probably serves as an exemplar for why I increasingly hate teaching classic experiments in my own field, except perhaps as cautionary tales. As the title suggests, this is a typical description of a series of experiments reported by Turner, Layton, and Simons (1975). Joe Hilgard aptly sums up what appeared to have happened:

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.
In summary, outside of perhaps one subgroup, assuming one believes the findings, there appears to not only be no priming of a weapon on aggressive behavior, but arguably the opposite: seeing a weapon in a vehicle suppressed horn-honking. When I was computing effect sizes for my recently published weapons effect meta-analysis, I noticed that overall, the Cohen's d was negative. That actually makes more sense to me.

Here is a screen shot of Table 3, which summarizes Study 3:

At bare minimum we might be able to make a case that privileged males (based on the cars they drove) are the one subsample that would honk their horns even when it seemed irrational. Otherwise, it appears that non-privileged males and females overall (no distinction is made on the whether or not female subjects drove new cars or older cars) showed either no effect or a suppression effect!

Late last decade, a student and I attempted a replication of the old Turner et al. (1975) research. In our case, we used a different DV, latency of horn-honking: in other words how long it took the driver behind the truck to start honking, measured in seconds (admittedly, my student's measure was crude: seconds were measured based on a confederate's wristwatch, when a stopwatch might have been more appropriate). The prime stimulus used was a bumper sticker of an AK-47 that was placed conspicuously on the rear window of the truck in the treatment condition. There was no sticker in the control condition. We ended up with null findings. If anything the presence of the AK-47 sticker trended (although nonsignificantly) in a negative direction. Admittedly our sample was small (cell sizes of 10 in each condition), and so my student merely wrote up the results to complete the requirement of a methods course he was in. It is possible that with a large enough sample, we would have been able to show fairly conclusively that drivers generally have the good sense not to try to provoke those who drive with weapons or even images of weapons. Or we may have ended up with a simple null finding, and given the low power of our study, that is a fair enough assessment.

I've often wondered what to make of this set of experiments, beyond the obvious conclusion that Turner et al. (1975) did not actually replicate the classic Berkowitz and LePage (1967) lab experiment. I am now wondering if there may be another plausible explanation. There is a body of research showing that individuals who are exposed to images of guns and knives embedded within an array of images are pretty good at primary threat appraisal. That is, they notice the images faster (based on reaction time) and they tend to show more caution (again based on reaction time) when primed with these images (see Sulikowski & Burke, 2014, for a recent set of experiments). Bottom line is that we may want to reinterpret the horn-honking experiments of Turner et al. (1975) and the work my student did with me as follows: weapons do not increase horn-honking behavior, to the extent we have used it as a proxy for aggression. Rather, it is likely that weapons either have no impact on horn-honking , or suppress the impulse to engage in horn-honking. This latter conclusion is consistent with the findings of some evolutionary psychologists who study threat appraisal. Individuals who encounter a potentially threatening stimulus are probably going to be more cautious around those who display such stimuli to the extent that they are motivated toward self-preservation. The adaptive response to seeing someone driving a vehicle with a gun on a gun-rack or a sticker of a weapons-grade firearm is to refrain from horn-honking, and if that is not possible, to at least delay horn-honking for as long as possible. At least that is an explanation that strikes me as sensible. Beyond that possible very tentative conclusion, I would suggest a lot of caution when interpreting not only field experiments purporting to demonstrate a link between short-term exposure to weapons or weapon images and aggressive behavioral outcomes, but lab experiments as well.In the meantime, stay skeptical.

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