Publication Date


Degree Program

Department of Psychology

Degree Type

Master of Arts


Previous investigations of the perception of 3-D shape from deforming boundary contours have focused on judgments of global shape (Cortese & Anderson, 1991), judgments of rigid vs. nonrigid motion (Norman & Todd, 1994), and object recognition (Norman, Dawson, & Raines, 2000). Raines and Norman (1999) provided the first study demonstrating that deforming boundary contours could support the accurate perception of local 3-D surface structure. The present set of experiments extend the Raines and Norman study by further investigating whether the distance from the boundary contour or the amount of overall boundary deformation affect the human ability to make local judgments about 3-D shape. In these experiments, the observers viewed either static or moving silhouettes of randomly shaped, smoothly curved objects (see Raines & Norman, 1999; Norman & Todd, 1996, 1998) before making ordinal depth judgments about two highlighted regions on the object's surface. Two local regions on the objects' surface were highlighted, and the observers were required to judge which of the two regions was closer to them in depth. In Experiment 1, the proximity of the highlighted regions to the objects' occlusion boundary was manipulated as well as the presence or absence of binocularly disparate views. Viewing regions closer to the boundary contour led to more precise judgments of ordinal depth than those regions further away. The results also showed that the presence of disparate views had a different effect on the two motion types. While stereoscopic views improved performance dramatically in the stationary conditions, the same disparities had little effect on performance in the motion conditions. In Experiment 2, the observers viewed apparent motion sequences that presented varying degrees of boundary deformation. Although performance decreased as the amount of deformation decreased, the observers' judgments remained relatively precise even at the smallest angles of oscillation. In summary, these results confirm previous findings showing that boundary contours, especially deforming contours, are an important source of information about 3-D shape. These results also show that information from the boundary contour propagates inward to regions far from the boundary and that even small amounts of deformation can support the accurate perception of ordinal depth.



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