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Jan Jaap van Assen, Roland Fleming; The influence of optical material appearance on the perception of liquids and their properties. Journal of Vision 2015;15(12):936. doi: 10.1167/15.12.936.
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© ARVO (1962-2015); The Authors (2016-present)
In everyday life, we readily identify liquids with different viscosities, such as water, honey, and tar. Previous findings suggest we use both shape and motion cues to judge viscosity. However, many common liquids also have distinctive optical properties (colour, glossiness and translucency), which could influence how we perceive them. Although optical properties are independent of viscosity, it seems plausible we may associate specific appearances (e.g. caramel, milk, water) with particular viscosities. On the other hand, the visual system may correctly discount optical properties enabling ‘viscosity constancy’. Here, we investigated whether optical characteristics influence viscosity perception. We simulated a wide range of viscosities from water to molten glass and rendered the resulting shapes with nine different surface characteristics. On each trial, subjects viewed a static frame from one such simulation (‘test’ stimulus) and performed two tasks. First, they adjusted the viscosity of a single frame from a later time-point in the simulation (‘match’ stimulus) to identify which shape appeared to have the same viscosity as the test. Match stimuli always had the same optical appearance (green goop). Next, observers rated six physical properties of the test stimulus. Subjects were good at matching viscosity apart from a consistent overestimation, especially of the runny liquids. Optical properties had almost no effect on matching, demonstrating good constancy. Wetness, liquidness, and sliminess ratings decreased systematically with increasing viscosity, with only weak effects of optical properties. In contrast, perceived shininess was invariant across viscosities but strongly affected by optical properties. However, perceived warmth and stickiness both showed substantial interactions between viscosity and optical properties, including non-monotonic relationships, suggesting subjects interpreted particular combinations of shape and reflectance as specific, recognizable liquids. These results suggest that although optical properties influence the perception of some characteristics of liquids, they have very limited influence on shape-based viscosity judgements.
Meeting abstract presented at VSS 2015
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