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Visual perception in general, and the visual perception of objects in particular, seems so immediate and effortless that it is difficult to comprehend its complexity. Consider, for example, the non-trivial question of what constitutes an object. Both philosophers and psychologists have occupied themselves with trying to find the necessary and sufficient properties of objects ( Hirsch, 1982 ; Wiggins, 1980 ). Based on infant research, Elizabeth Spelke and her colleagues have defined objects as solid entities that (a) exhibit spatio-temporal continuity, (b) cohere within their boundaries when they move, and (c) move only when contacted by another object ( Spelke, 1990 ; Spelke, Guthiel, & Van de Walle, 1995 ). On Spelke's definition, animals and immaterial entities are excluded from the object category, and well they should be, at least for common usage of the term “object.” Bloom (1996) correctly excludes other entities, including puddles, shadows, holes, illusory objects, and parts of objects (e.g., fingers and cup handles). Ittelson (1996) excludes pictures of objects because they are two-dimensional (2-D) rather than three-dimensional (3-D), as real objects are. Distinctions between those entities that count as real objects and those that do not are critical if one is concerned with classifying those entities we judge or know to be real objects. However, most investigators ... log in or subscribe to read full text