PARTS OF VISUAL FORM - PSYCHOPHYSICAL ASPECTS

Part-based representations allow for recognition that is robust in the presence of occlusion, movement, growth, and deletion of portions of an object, and play an important role in theories of object categoriza tion and classification. A partitioning theory for visual form is prop osed that is based on two types of parts: Limb-based parts arise from a pair of negative curvature minima with evidence for 'good continuati on' of boundaries on one side; neck-based parts arise from narrowings in shape. The motivation for this model is computational requirements for recognition. The psychophysical relevance of this model is address ed by measuring intrasubject and intersubject consistency in partition ing tasks and comparing perceived and computed parts. A series of expe riments were performed in which subjects were required to partition a variety of biological and nonsense two-dimensional shapes into perceiv ed components. Specifically, it was examined (1) whether a subject det ermines components consistently across different trials of the same pa rtitioning task, (2) whether there is evidence for consistency between subjects for the same partitioning task, and (3) how the perceived pa rts compare with limbs and necks resulting from the computational mode l. The results are interpreted as suggesting that there are high level s of both intrasubject and intersubject consistency and that a large m ajority of the perceived parts do in fact correspond to the parts comp uted on the basis of our model. The implications of our model are disc ussed in relation to previous experimental results. Intuitive observat ions concerning the relationship between parts of visual form and thei r function are then presented. Finally, a role is envisioned for parts in figure/ground segregation; the notion of a 'parts receptive field' through which parts can serve as an intermediate representation betwe en local image features, eg edges, and global object models, is sugges ted.