Curran, William; (1995) Integration of shading and texture cues in the perception of solid shape. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In constructing a three-dimensional perception of our environment the visual system draws on a number of different sources of information available in the image. It is often assumed that, at the early stages of this process, these cues to three-dimensional shape are processed independently, and are later integrated to form the three-dimensional percept. The experiments in this thesis address a number of issues relating to the integration of shading and texture cues. These include 1) At what level of representation are shading and texture cues integrated. 2) Is the integration of these cues a linear or non-linear process. 3) What factors influence the weights assigned to cues. 4) Is shape from shading and texture a local or global process. 5) What texture properties do subjects use to extract curvature information. and, finally, 6) What factors influence the perceived degree of curvature of a convex surface. Two main paradigms, perturbation analysis and 3D curvature contrast, were employed in an attempt to answer these questions. The results of the experiments described in this thesis lead to the following conclusions: a) the locus of integration for the shading and texture cues used in these experiments is more likely to be a curvature map than a depth map; b) the integration of these cues is not best described by a linear model, but by a non-linear model; c) although the shading and texture cue weights are robust across a number of different viewing conditions, they are influenced by some context manipulations as well as by the cues' availability and reliability; d) 2D line curvature appears to be the primary source of texture curvature information used by subjects in these experiments; e) the processing of shape from shading and texture cannot be a purely local operation, but appears also to include global operations; and, finally, f) although the perceived curvature sign of a convex surface defined by shading may be disambiguated with the inclusion of other cues, it is demonstrated that subjects' perception of the surface's degree of curvature may be influenced by other factors. These include light source position and the curvature of the background in which the surface is embedded.

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