Categorizing natural objects: a comparison of the visual and the haptic modalities
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Although the hands are the most important tool for humans to manipulate objects, only little is known about haptic processing of natural objects. Here, we selected a unique set of natural objects, namely seashells, which vary along a variety of object features, while others are shared across all stimuli. To correctly interact with objects, they have to be identified or categorized. For both processes, measuring similarities between objects is crucial. Our goal is to better understand the haptic similarity percept by comparing it to the visual similarity percept. First, direct similarity measures were analyzed using multidimensional scaling techniques to visualize the perceptual spaces of both modalities. We find that the visual and the haptic modality form almost identical perceptual spaces. Next, we performed three different categorization tasks. All tasks exhibit a highly accurate processing of complex shapes of the haptic modality. Moreover, we find that objects grouped into the same category form regions within the perceptual space. Hence, in both modalities, perceived similarity constitutes the basis for categorizing objects. Moreover, both modalities focus on shape to form categories. Taken together, our results lead to the assumption that the same cognitive processes link haptic and visual similarity perception and the resulting categorization behavior.
KeywordsVision and haptics Similarity measures Categorization Perceptual spaces
All seashells are items of loan from the natural history museum Stuttgart, Germany (Am Löwentor, Staatliches Museum für Naturkunde Stuttgart). We thank Hans-Jörg Niederhöfer for providing the seashells and helping to select an adequate set of stimuli. This study was partially supported by the WCU (World Class University) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (R31-2008-000-10008-0).
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