Categorization and Object Shape

Abstract

Categorization is essential for perception and provides an important foundation for higher cognitive functions. In this review, I focus on perceptual aspects of categorization, especially related to object shape. In order to visually categorize an object, the visual system has to solve two basic problems. The first one is how to recognize objects after spatial transformations like rotations and size-scalings. The second problem is how to categorize objects with different shapes as members of the same category. I review the literature related to these two problems against the background of the hierarchy of transformation groups specified in Felix Klein’s Erlanger Programm. The Erlanger Programm provides a general framework for the understanding of object shape, and may allow integrating object recognition and categorization literatures

Transformation Direction Influences Shape-Similarity Judgments

“…Similarity ratings decreased with increasing transformation distance, F(3, 114) 5 610.93, p < .001, p rep 5 .99, Z 2 5 .94, confirming previous evidence that perceived similarity depends on transformation distance (Graf et al, 2008;Hahn et al, 2003). The central question, however, was whether transformation direction influenced similarity judgments.…”

“…Previous evidence in favor of transformational approaches to similarity has centered on transformation distance and its relation to perceived similarity (Graf et al, 2008;Hahn et al, 2003). Our aim in the experiments reported here was to investigate the potential impact of transformation direction on similarity.…”

“…In this literature, many findings indicate that object recognition performance depends on the amount of geometric transformation (such as rotation, size scaling, and translation) necessary for the alignment of input representation and memory representation (e.g., Gauthier & Tarr, 1997; Graf, Kaping, & Bülthoff, 2005; Jolicoeur, 1990, 1992; Tarr, 2003; Tarr & Gauthier, 1998). This transformational framework can be extended to basic-level categorization if deforming transformations are also considered (Graf, in press; Graf, Bundesen, & Schneider, 2008). The shape variability within familiar basic-level categories can be accounted for with nonlinear (topological) shape transformations that correspond to morphing (see Fig.…”

“…1). Categorization performance has been found to depend systematically on the amount of topological transformation (morphing) between two members of the same category (Graf, 2002, in press; Graf et al, 2008). Categorization research has also shown that displaying intermediate items along a transformational path, and hence clarifying transformational relationships, enhances the similarity of the end points (Zaki & Homa, 1999; Hockema, Blair, & Goldstone, 2005).…”

Visuo-haptic multisensory object recognition, categorization, and representation

“…Categorization facilitates recognition and is critical for much of higher-order cognition ( Graf, 2010 ); hitherto, the emphasis in terms of perceptual categorization has been almost exclusively on the visual, rather than the haptic, modality. More recently, however, a series of studies has systematically compared visual and haptic categorization.…”