PERCEPTUAL CATEGORIES FOR SPATIAL LAYOUT

The central problems of vision are often divided into object identific ation and localization. Object ect identification, at least at fine le vels of discrimination, may require the application of top-down knowle dge to resolve ambiguous image information. Utilizing top-down knowled ge, however, may require the initial rapid access of abstract object c ategories based on low-level image cues. Does object localization requ ire a different set of operating principles than object identification or is category determination also part of the perception of depth and spatial layout? Three-dimensional graphics movies of objects and thei r cast shadows are used to argue that identifying perceptual categorie s is important for determining the relative depths of objects. Process es that can identify the causal class (e.g. the kind of material) that generates the image data can provide information to determine the spa tial relationships between surfaces. Changes in the blurriness of an e dge may be characteristically associated with shadows caused by relati ve motion between two surfaces. The early identification of abstract e vents such as moving object/shadow pairs may also be important for dep th from shadows. Knowledge of how correlated motion in the image relat es to an object and its shadow may provide a reliable cue to access su ch event categories.