ABSTRACT
DEMAND CHARACTERISTICS OF VISUAL ENCODING A primary goal of visual encoding is to determine the nature and motion of the objects in the surrounding environment. In order to plan and coordinate actions, we need a functional representation of the scene layout and of the spatial con‰guration and the dynamics of the objects within it both in the picture plane and in depth. e properties of the visual array, however, have a metric structure entirely diŠerent from those of the spatial con‰guration of the objects. Physically, objects consist of aggregates of particles that cohere together. Objects may be rigid or Œexible, but in either case, an invariant set of particles is connected to form a given object. e visual cues (such as edges or gradients) conveying the presence of objects
CONTENTS Demand Characteristics of Visual Encoding 163 eoretical Analysis of Surface Representation 165 Need for 3D Surface Representation 167 Evidence for a Functional Role of 3D Surface Representation 169 Cortical Organization of the Surface Representation 174 e Surface Correspondence Problem 177 Conclusion 181
to the brain or to arti‰cial sensing systems, however, share none of these properties. e visual cues conveying the presence of objects may change in luminance or color, and they may be disrupted by reŒections or occlusion by intervening objects as the view point changes. e various cues such as shading, texture, color binocular disparity, edge structure, and motion vector ‰elds may even carry inconsistent object information. As exempli-‰ed by the dodecahedron drawn by Leonardo da Vinci (Figure 9.1a), any of these cues may be sparse, with a lack of information about the object structure across gaps where cues are missing. Also, any cue may be variable over time. Nevertheless, despite the sparse, inconsistent, and variable nature of the local cues, we perceive solid, three-dimensional (3D) objects by interpolating the sparse depth cues into coherent spatial structures generally matching the physical con‰guration of the objects.
