Integration of Size and Binocular Disparity Visual Cues in Manual Depth-Control Tasks

Humans rely on a plethora of visual cues to inform judgments of the depth or range of a particular object or feature. One source of information is binocular (or stereo) vision, enabled by the slight differences in the images between the two eyes. Another source of information is the size, in visual angle, of the feature or object. Although it is possible to provide binocular disparity in a display, it typically implies increased system cost or lower update rates; therefore it is useful to determine how critical it is to provide binocular disparity to the user. This paper describes the results of several experiments investigating the integration of stereo and size cues in performing manual control tasks. In the first experiment, a visual cue integration model was developed for two types of manual control tasks (rate-control and acceleration-control) and different levels of cue salience. The results of this experiment were that stereo disparity dominated judgments of depth position, while size dominated judgment of depth rate. From this experiment, it was hypothesized that stereo disparity would do more to improve performance on rate-control tasks more than on acceleration-control tasks. Two additional experiments were conducted, with and without stereo display, to test this hypothesis at different update rates. The results confirmed that while stereo disparity improved performance on rate-control tasks, it did not improve performance on acceleration-control tasks; in fact, performance was reduced with stereo disparity when the display method reduced update rate below a particular threshold.