Can observers recognize novel views of three-dimensional (3-D) objects, created by rotations in depth from a single familiar view? Three experiments using 3-D model objects are reported demonstrating that: (a) subjects can indeed recognize novel views under these circumstances, and (b) recognition accuracy depends on the types of objects employed. More precisely, subjects successfully recognized geometricallyregular and irregular objects rotated by 180 degrees about the vertical ^ ) axis. However, only geometricallyregular objects w o e recognized w h e n rotated similarly by 9 0 degrees. Thesefindingscannot be easily accommodated by contemporary object-centered or viewer-centered theories of shape-based object recognition, which m a k e no provisions for rqnesenting different types of objects uniquely. Alternatively, thesefindings support a theory in which inferences about objects' 3-D shapes are generated from information implicit in their two- dimensional (2-D) bounding contours, or silhouettes (Johnson, 1993). Such inferences m a y be premised on rules that C2q)ture importantregularities between 2- D bounding contours and 3-D surface geometry (e.g., Beusmans, Hofiman, & Bennett, 1987; Richards, Koenderink, & Hoffinan. 1987).

A set of tasks developed in accordance with Kosslyn. Van Kleeck. & Kirby's (1990b) neurologically plausible model of visual mental imagery was used to explore effects of aging on specific component processes involved in image generation and maintenance. Contrary to the widely held belief that age differences in cognition are attributable to a single mechanism of global effect (e.g., a reduction in critical processing resources, Salthouse, 1988), results indicate that processes involved in visual mental imagery are differentially age-sensitive. More precisely, components required to actively maintain images are particularly sensitive to effects of aging, while those that access visual information from memory are not especially affected. Advantages of a componential approach to understanding age differences in cognitive processing are disscussed, as well as the potential for such agerelated changes to be a readily exploitable source of information regarding the functional architecture of cognition.