Salient material properties and haptic volume perception: The influences of surface texture, thermal conductivity, and compliance

Abstract

We investigated the influences of surface texture, thermal conductivity, and compliance on the haptic perception of the volume of small cubes. It was hypothesized that an object containing highly salient material properties would be perceived as larger in volume than the same object without these properties. Blindfolded subjects were asked to explore pairs of cubes differing in their material properties and to select the one with the larger volume. The results showed that, counterintuitively, a smooth cube was perceived as being significantly larger than a rough cube of the same physical volume, with average biases of about 19 %. Furthermore, cubes with a higher thermal conductivity were perceived as significantly larger than cubes with a lower thermal conductivity (average bias of about 7 %). In addition, the magnitude of the bias in this condition was not changed by increasing or decreasing the temperature of the test objects, suggesting that the effect of thermal conductivity could not be attributed directly to the heat flow. Finally, a hard cube was perceived as significantly larger than a soft cube of equal physical volume, with an average bias of about 25 %. These results reveal that the studied material properties have significant and consistent influences on the haptic perception of volume. The observed biases provide an indication of the levels at which the processing of haptic information on volume and material properties occurs.Keywords Haptics . Roughness . Coldness . HardnessObjects that we encounter in our environment can differ along a number of dimensions, like shape, size, and material. Each dimension contributes in its own way to the percept of the object, and the perception of one particular dimension may be influenced by the presence of other physical object properties. The present study focuses on the influence of salient material properties on haptic perception of the volumes of objects. Previous studies have shown that volume perception is not veridical. We have shown that small threedimensional objects with the same physical size (i.e., volume) but differing in shape are perceived as being different in size (Kahrimanovic, Bergmann Tiest, & Kappers, 2010). In that study, blindfolded subjects had to explore tetrahedrons, cubes, and spheres by touch. On each trial, they were asked to compare two differently shaped objects and to indicate the one that they perceived as being larger in volume. The largest effect of shape on volume perception was found for the comparison of tetrahedrons and spheres. A tetrahedron was perceived as being equal in volume to a sphere that was on average about 48 % larger in volume than the tetrahedron. Similarly, tetrahedrons were perceived as being larger than cubes of the same physical volume, and cubes were perceived as being larger in volume than spheres. Additional analyses of these results showed that the occurrence of these volume biases could be explained by the subjects' tendency to base their volume judgment on the surface areas of the objects. H...

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