Publication Date

8-1-2003

Degree Program

Department of Psychology

Degree Type

Master of Arts

Abstract

The informativeness of a cast shadow or silhouette boundary contour for the perception of 3-D object shape has been investigated for a long time. Some researchers have focused on the informativeness of static shadows (Attneave, 1954; Koenderink, 1984; Richards, Koenderink, & Hoffman, 1987; Norman, Phillips, & Ross, 2001; Tse, 2002) while other researchers have focused on the informativeness of moving or deforming shadows (Miles, 1931; Wallach, & O'Connell, 1953; Norman, & Todd, 1994; Norman, Dawson, & Raines, 2000; Norman, & Raines, 2002). Past research has shown that changing the angle of illumination does not affect the perception of 3-D shape from cast shadows (Norman et al., 2000). The current experiment extends the prior experiments by further investigating whether curved background surfaces (with both positive and negative Gaussian curvature) affect the perception and recognition of 3-D object shape from deforming and/or static cast shadows. In this experiment, the observers viewed either deforming or static shadows of naturally shaped objects (bell-peppers) cast onto either flat, hemispherical, or saddle-shaped surfaces. The results revealed significant main effects of motion (deforming vs. static shadows), object, and the type of background surface. The results revealed that there were also a number of significant interactions involving particular objects, the presence or absence of motion, and the type of background surface. The observers' ability to recognize objects from deforming shadows was higher than their ability to recognize objects from static shadows. In addition, the observers' ability to recognize objects from the shadows cast onto the hemisphere background surface was generally as accurate as their ability to recognize objects from the shadows cast onto the flat plane. However, the observers' ability to recognize the objects was reduced when the shadows were cast onto the saddle background surface. The results of the experiment confirm previous findings showing that shadow boundary contours, especially deforming contours, are perceptually informative and help observers to perceive and recognize 3-D object shape. This experiment also extends previous studies by showing how differently curved background surfaces affect the perception and recognition of 3-D object shape.

Disciplines

Cognition and Perception | Psychology