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Abstract:
Rosch et al. (1976) and others have argued that the shape of objects is a fundamental determinant of category structure. In a previous study, we observed that after ten hours of visual exposure to a series of novel, 3D objects, subjects asked to perform free categorization in a sequential presentation task did so primarily on the basis of shape differences (6/10) as opposed to texture (1/10) or a combination of both (3/10) (weight of texture relative to shape: M=26, SE=10). In contrast, no such effect was found after ten hours of haptic exposure, i.e., shape and texture were equally weighted (M=55, SE=8). We hypothesized that, prior to experience, subjects are equally likely to use any weighting strategy, but that lengthy visual experience makes shape-dominated groupings more likely. Thus, in Experiment 1, subjects categorized objects either without any prior experience or after 1h of similarity judgments. Mean shape/texture weight was not significantly different from 50 in either condition, a result in agreement with our hypothesis. In Experiment 2, we tested whether the same pattern would hold for two different types of categorization tasks. In the first task, 10 naïve subjects viewed all objects simultaneously and sorted them into any number of groups. In the second task, 10 naïve subjects were sequentially shown two pairs, each consisting of the target and one of two category prototypes, and indicated which pair of objects was drawn from the same group. Contrary to our expectation, subjects in the array task relied on texture differences (M=80, SE=7), while subjects in the pair task relied more on shape (M=32, SE=3). These results demonstrate that shape differences do not always act as the key determinants of category structure; the sensory modality used to experience objects, the length of exposure, as well as task parameters also play a role.
