Stereoscopic 3D (S3D) displays offer the capability to enhance user performance on a variety of depth tasks. However, the benefit derived from viewing S3D depends in part on the magnitude of binocular disparity that is displayed. Surprisingly few studies have directly investigated the relationship between disparity and depth task performance. The studies that have been conducted suggest that a minimum amount of disparity (10-50 arc min) may be needed to improve performance over conditions in which no S3D is present, but it is unclear the extent to which performance might improve with increases in disparity beyond this range.From a human factors perspective, there are compelling reasons for using binocular disparities that are smaller than a strict geometrical interpretation of the scene would require (i.e., microstereopsis); one reason is to make the viewing experience more comfortable. This is important because S3D displays appear to cause a variety of simulator sickness-type problems for as many as 25-50% of users (including eye strain, headache, nausea, etc.). Preliminary evidence on the use of microstereopsis suggests that it does indeed result in a more comfortable and less fatiguing depth percept, particularly if binocular disparity is limited to a maximum of about 60 to 70 arc min (the One Degree Rule). But does microstereopsis also negate the performance benefits of stereopsis? How much can disparities be reduced before performance decrements are noticeable, and how comfortable are these disparities? Is there a stereo "sweet spot" in which both performance and comfort are high? And is this sweet-spot dependent on the particular depth task being tested?Results from a simple 2 degree-of-freedom (DOF) virtual precision object alignment task showed that when averaged across participants, maximum performance was achieved when disparity was limited to +/- 80 or 100 arc min of disparity during a 30 minute session. Performance with S3D cues improved alignment accuracy by up to 80% compared to no stereo cues, though several participants received an inconsistent benefit, and in a few cases, S3D resulted in detrimental performance. The tested magnitudes of disparity limits were also generally comfortable, although a significant correlation between increasing disparity and decreasing comfort was confirmed. Several optometric measures (e.g. stereoacuity, fusion ranges) predicted performance, but not comfort, on S3D displays.Results from a more complex 5 DOF virtual precision object alignment task showed that the best performance was achieved with disparity limits from +/- 60 to 100 arc min of disparity. Again, the tested magnitudes of disparity limits were generally comfortable, and several optometric measurements predicted performance but not comfort. Overall, the results suggest that the One Degree Rule for stereoscopic disparity limits can be expanded for near-viewing desktop applications. The results also suggest that while camera separations resulting in microstereopsis showed improved performance over no-stereopsis… Advisors/Committee Members: Watamaniuk, Scott (Committee Chair).