Visualization of three‐dimensional structure during computer‐aided design

The visual image presented to an engineer using a computer‐aided design (CAD) system influences design activities such as decision making, problem solving, cognizance of complex relationships, and error correction. Because of the three‐dimensional (3‐D) nature of the object being created, an important attribute of the CAD visual interface concerns the various methods of presenting depth on the display's two‐dimensional (2‐D) surface. The objective of this research is to examine the effects of stereopsis on subjects’ ability to (a) accurately transfer to, and retrieve from, long‐term memory spatial information about 3‐D objects; and (b) visualize spatial characteristics in a quick and direct manner. Subjects were instructed to memorize the shape of a 3‐D object presented on a stereoscopic CRT during a study period. Following the study period, a series of static trial stimuli were shown. Each trial stimulus was rotated (relative to the original) about the vertical axis in one of six 36° increments between 0° and 180°. In each trial, the subject's task was to determine, as quickly and as accurately as possible, whether the trial object was the same shape as the memorized object or its mirrored image. One of the two cases was always true. To assess the relative merits associated with disparity and interposition, the two depth cues were manipulated in a within‐subject manner during the study period and during the trials that followed. Subject response time and error rate were evaluated. Improved performance due to hidden surface is the most convincing experimental finding. Interposition is a powerful cue to object structure and should not be limited to late stages of design. The study also found a significant, albeit limited, effect of stereopsis. Under specific study object conditions, adding disparity to monocular trial objects significantly decreased response time. Response latency was also decreased by adding disparity information to stimuli in the study session.