Strong Disgust
In a previous post, I wanted to call attention to the way that people have used the word “strong” in the context of the term “strong reciprocity” by applying the same style of reasoning to fear. A key issue in these discussions is why people show a particular pattern of behavior even when the behavior can’t, as a matter of fact, have the effect for which it was selected. Why be nice in one shot games, given that reciprocity is impossible? Why be afraid of the projected image of a cave troll, given that the image of the cave troll poses no real threat?
A new paper available online (pay wall) in Evolution and Human Behavior by Stephen Ryan and colleagues that speaks to a similar issue for disgust, making a fairly strong claim in the title: “Facial disfigurement is treated like an infectious disease.” The paper reports some research by a team in Australia – including, full disclosure, some friends of mine – and speaks to the question of why people show disease-avoidance behaviors even when they “know” that the person in question can’t communicate disease. Why avoid coming into contact with something that isn’t, as a matter of fact, likely to be contaminated?
The spirit of this work has ties to my Penn colleague Paul Rozin’s famous and fun work in which he asked subjects to do things like drinking from a glass of water into which a sterilized cockroach had been dipped. Even though subjects “know” the water is safe, there’s a certain, understandable, reluctance.
Ryan et al. had people come into the lab to perform what was ostensibly an imitation task. Subjects watched a video of a person interacting with some objects, such as placing a snorkel in their mouth. The task was to do just what the person in the video did with the object. Crucially, some of the models the subjects viewed had been made up to look like they had the flu – and were therefore presumably contagious – or made up with a very visible birth mark (a “port wine stain”) on their face. The question was, even though the birth mark doesn’t indicate the presence of an actual contagion, would subjects who saw this model be less willing to put the snorkel in their mouth?
Figure 1 from Ryan et al
Briefly yes. (See their Figure 1.) People treated artifacts handled by the model with the birthmark the same as they handled the artifacts from the person who looked like they had the flu.
The explanation, which is likely familiar to many readers of this blog, draws on basic decision theory. The design of psychological systems should reflect the fact that they need to maximize expected value, not percent correct. In the case of contagion, because the cost of a miss is high – that is, coming into contact with a potentially pathogen-infested object – the system seems to be designed to shy away from contact with things that have themselves been in contact with people who deviate from the healthy phenotype even when there is good evidence – in this case, one’s knowledge about birth marks – that the origin of the deviation means that it is more or less safe to do so. Because the cost is high, the experienced low by non-zero probably directs the subject away from the “risky” behavior.
Importantly, to connect back up to the point above, subjects showed similar amounts of disgust expressions in the birth mark conditions, and, further, subjects knew – that is, reported explicit knowledge that – the people with the birthmark posed no special threat of contagion. In the authors’ own words:
Consistent with our prediction, participants demonstrated disgust at the prospect of contacting props touched by the birthmark and influenza confederates, and avoided contact with these props especially when the contact was more intimate (i.e., face, mouth). These reactions to the confederates with influenza and a birthmark would seem to be implicit because, when asked at the end of the study, participants reported influenza as being more contagious (M=6.4 vs. 1.3) and more lethal (M=3.7 vs. 1.4) than a birthmark. Thus, even though participants knew the birthmark confederates were noncontagious, they responded to them as though they were and in a largely identical manner to the confederate with an infectious disease.
So, do people show “strong disgust,” avoiding contact with objects even when they “know” that there’s no particular contagion risk? Apparently so.
Reference
Ryan, S., Oaten, M., Stevenson, R. J., & Case, T. I. (in press). Facial disfigurement is treated like an infectious disease. Evolution & Human Behavior.
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