Disgusted people have enhanced ability to spot dirt

The cool, calm extravert - that's the emotional profile that our culture puts on a pedestal. Prudes, introverts and scaredy-cats just aren't fashionable.

Yet there's mounting psychological research showing that unpopular emotional traits often come with advantages. The anxiously attached are quicker to detect danger, such as smoke in a room; those with trait anxiety have fewer accidents; introverts speak in a way that's perceived as more trustworthy. Now Gary Sherman and his colleagues have published research showing how prudish disgust-sensitivity is associated with a superior ability to detect impurities.

Over one hundred students had to judge repeatedly which of four squares on a computer screen was the odd-one-out in terms of its shading. The squares were either light grey against a white background, with one slightly darker or lighter than the others (akin to spotting dirt against a white background); or they were dark grey against a black background, with one slightly darker or lighter than the others.

Students more prone to disgust (they agreed with statements like "it would bother me to see a rat run across my path") tended to have heightened sensitivity for spotting grey shades against a white background, similar to spotting dirt on a clean surface. They displayed no such heightened sensitivity at the other end of light spectrum - grey on black.

A second study was similar, but this time students more prone to disgust had heightened sensitivity when identifying digits written in light grey against a white background (yet they were no better at spotting grey digits against a mid-grey background).

In a final study, looking at disgusting pictures (e.g. maggots on meat) boosted the ability of disgust-sensitive participants to spot grey digits against a white background. Participants low in disgust sensitivity didn't show this response to the pictures, perhaps because they were unmoved by them.

The effect documented here is a form of perceptual tuning, like the way in infancy we gradually lose our ability to hear sounds that feature in foreign languages. It's not clear if being disgust prone leads to more exposure to clean white surfaces, and so more practice and superior ability at seeing darker shades against a light background. Or if instead, some people have heightened sensitivity at this end of the colour spectrum, which has the effect of making them more prone to disgust. Or both, in a self-perpetuating cycle.

"Disgust not only makes people want to avoid impurities," the researchers said, "but also makes people better able to see them."

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Sherman, G., Haidt, J., and Clore, G. (2012). The Faintest Speck of Dirt: Disgust Enhances the Detection of Impurity. Psychological Science, 23 (12), 1506-1514 DOI: 10.1177/0956797612445318

--Further reading--
More research items on disgust.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.