Abstract
How does the human visual system represent 3D shape? One hypothesis is that object shape is represented in terms of its volumetric components and their spatial configuration. Another hypothesis predicts that 3D shape is represented in terms of regions of edge contour corresponding to surfaces. Recently Leek et al (2005) showed that there is a performance advantage in whole-part matching for configurations of edge contour that corresponds to surfaces or volumetric components as opposed to nonvolumetric shape regions. In this study we examined the role of three types of shape primitives: volumetric components, surfaces and non-volumetric regions in the representation of geometrically regular and irregular 3D shape. In Exp.1 participants were required to match object parts to novel 3D objects and in Exp.2 to decide whether an object was familiar or not following an object related or unrelated prime. The results showed (i) better performance when edge contour corresponded to surfaces or volumetric components as opposed to nonvolumetric closed regions; and (ii) regular objects benefited from surface groupings corresponding to volumetric components, whilst irregular forms benefited from surface groupings regardless of whether they corresponded to a volumetric part or not. The results are discussed in terms of the surface-based model of 3D shape representation.