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Hecht, H., & Proffitt, D. R. (1995). The price of expertise : Effects of experience on the Water-Level Task. Psychological Science, 6(2), 90-95.

When shown a tilted container, people often fail to appreciate that the surface of the liquid contained within should remain horizontal with respect to the ground. This study investigated how amenable this bias is to experience in relevant everyday situations. Surprisingly, liquid surfaces that waitresses and bartenders considered natural deviated even more from horizontal than was the case for comparison groups. This finding is, to our knowledge, the only documented case in which performance declines with experience. We suggest that practical experience promotes a functionally relative perspective, in which the orientation of the liquid's surface is evaluated relative to that of its container as opposed to being related directly to the surrounding environment. The container-relative perspective, in turn, evokes a perceptual bias that is responsible for the systematic errors observed on this task.

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