Perception
Do we use how wet something looks to spot germs?
Open access · cc by · source: Europe PMC
People judged how wet dough was very accurately from its shiny highlights, and they found it most disgusting and risky when it was moderately wet rather than dry or very runny.
Study at a glance
- Design
- Human experiment — Within-subject psychophysics: eight photographs of dough varying in water content were ranked (Exp 1) or paired-compared (Exp 2) for moistness and rated for disgust, avoidance and contamination risk.
- N
- N=37 · 22 female undergraduates in Experiment 1 and a separate group of 15 in Experiment 2; n is the two groups combined.
- Population
- Female Japanese undergraduate students
- Outcome
- Perceived moistness scale values; ratings of disgust, motivation to avoid touching, and perceived contamination risk
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Key findings
Actual water content predicted perceived moistness almost perfectly (R-squared of 0.99 in Experiment 1), and so did the number of bright highlight areas, which fell as the dough got wetter and smoother. Disgust, avoidance and contamination-risk ratings did not rise in a straight line; they followed an inverted U, peaking for dough with roughly 33 to 39% moisture. Experiment 2 replicated these patterns, although the effects of water content on the disgust-related ratings were smaller.
Methodology
The researchers photographed flour-and-cocoa dough mixed with increasing amounts of water, giving eight images whose water content ran from about 28.6 to 42.9% of the dough's weight. In Experiment 1, 22 women ranked the images from least to most moist; in Experiment 2, a new group of 15 women chose the moister image in repeated pairs. In both experiments participants also rated each image for disgust, desire to avoid touching it, and perceived risk of contamination, and the authors counted the bright specular highlight patches in each image.
Limitations
The samples were tiny, all female and not sized in advance, so the findings may not generalise to men or to other populations. Only one material (dough) and eight images were used, and the photos also differed in surface shape and streaks, so other visual features such as spatial frequency could explain the ratings. The authors note that moderately wet dough may simply have resembled feces, so the disgust peak could reflect what the object looked like rather than moisture itself. The study also cannot show that these judgments track real pathogen risk; in fact very wet dough was rated as less risky even though microbes thrive in more water.
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