Considered as a strictly conceptual question, the superficial association appears as an irrelevance. And in some sense we all know this: we would presumably mostly agree if asked with the claims that physically clean people can do awful things, and physically dirty people can act nobly. But how powerful is the association when we’re not asked questions that force us to be a bit more conceptually careful?
This paper reports on a series of related experiments, all suggesting that the association has significant measurable effects in cases where it should be conceptually irrelevant. More specifically the authors sought to investigate:
(i) whether a threat to moral purity activates a need for physical cleansing (i.e., the Macbeth effect) and (ii) whether physical cleansing is actually efficacious in helping people cope with moral threats.The paper reports four separate, related, studies. Here’s a brief gloss of each, and its punchline:
Study 1: Subjects recalled either an ethical or unethical deed from their past, and then describe the emotions (not the deed itself). All then engaged in a word completion task, and subjects who had recalled an unethical deed completed words in cleaning related ways (e.g. W _ _ H, which could be ‘wash’ or ‘wish’) more frequently than subjects in the ethical recall condition. This suggests that thinking about unethical deeds makes cleaning related concepts more accessible.
Study 2: Subjects told that the study was about handwriting and personality, copied a short story in the first person, identical except for the final sentence which in one case suggested an ethical act, in the other an unethical one. They were then asked to rate the desirability of a range of products. Subjects who had copied the story with the unethical ending reported the cleaning products as more desirable. (See figure.)
Study 3: These subjects did the same recall task as in Study 1, but were then offered one of two different free gifts for their participation, either a pencil or an antiseptic wipe. Subjects in the unethical recall condition selected the antiseptic wipe more frequently.
Study 4: Again the same recall task (Study 1, 3) was used, except that all subjects recalled an unethical deed. Half of the subjects were then asked to clean their hands. Subjects who had cleaned their hands agreed to participate in a further experiment for no reward than subjects who had not. This suggests that the cleaning in some sense reduces the subjects’ perceived guilt.
What’s going on here? We don’t really know yet – this work measures some related effects, but sheds no direct light on mechanisms, including mechanisms of development. As the authors note, there’s already work suggesting that moral and what they call ‘pure’ disgust (such as reaction to rotting meat) are associated both with similar facial expressions and with overlapping brain activation (Moll et al, 2005). Overlapping brain activation isn’t on its own that impressive, although the overlapping brain activation isn’t that hard to come by, and the subjects in the Moll et al study were reading statements which seems to me a noisy kind of stimulus.
I reckon we could find out a lot about the mechanisms here from further investigation in non-human social animals. In fact ‘we’ probably have, it’s just that I need to go and do some more reading. I’d also be interested to see work on how early in human development the effect is measurable. We already know that preverbal infants have preferences that are at least relevant to moral questions.
As I said earlier, this research isn’t new. It’s been blogged a bit already, including here and here, and covered in the New York Times.
References: Moll, J., de Oliveira-Souza, R., Moll, F. T., Ignacio, F. A., Bramati, I. E., Caparelli-Daquer, E. M., et al. (2005). The moral affiliations of disgust: A functional mri study. Cogn Behav Neurol, 18(1), 68-78. [Link]
Zhong, C. (2006). Washing Away Your Sins: Threatened Morality and Physical Cleansing. Science, 313(5792), 1451-1452. DOI: 10.1126/science.1130726