A fascinating paper in the December, 2012 issue of Psychological Science by Gary Sherman, Jonathan Haidt, and Gerald Clore explores the influence of disgust on the ability to see potential impurities. The researchers reasoned that people generally associate white with purity and cleanliness. That is why many bathroom fixtures are white. Impurities are changes from that white color. They suggested that disgust may make people particularly sensitive to changes from white compared to changes from a dark gray.

To test this proposal, participants were shown a white or a dark gray background on a computer screen. A numeral was presented on the screen in a shade that differed only slightly from the background. Participants simply had to identify what numeral was presented by pressing a button.

In one study, the researchers used a scale that measured people’s trait disgust. That is, some people are highly sensitive to disgusting elements in while other people are not strongly bothered by disgusting things.

People’s level of disgust was not related to their ability to detect the numbers against a dark background. However, people with higher levels of trait disgust were better able to detect the numbers against a white background than were people with lower levels of trait disgust. So, disgust was specifically related to people’s ability to see changes from white.

In a follow-up study, participants were shown disgusting and -inducing pictures (as well as control versions of those pictures that were scrambled). The fear-inducing pictures made people more sensitive to the numerals at both ends of the spectrum. The disgusting pictures only changed people’s ability to see the numerals for the white background, though this effect was obtained primarily for people with a to disgust. The authors suggest that people with a low sensitivity to disgust did not find the pictures (which showed things like insects and trash) to be that disgusting.

These findings demonstrate how our emotional states tune our ability to perceive. Disgust is the emotion we feel when we are in the presence of impurity. When we are disgusted or worried about the possibility that there will be disgusting things around, then we become particularly sensitive to the potential impurities in the environment. This is a good mechanism to have, because impurities can ultimately make us ill.

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