Augmented reality provides its user with additional information not available through the natural real-world environment. This additional information displayed to the user potentially poses a risk of perceptual and cognitive load and vision-based difficulties. The presence of real-world objects together with virtual augmenting information requires the user to repeatedly switch eye focus between the two in order to extract information from both environments. Switching eye focus may result in additional time on user tasks and lower task accuracy. Thus, one of the goals of this research was to understand the impact of switching eye focus between real-world and virtual information on user task performance.

Secondly, focus depth, which is an important parameter and a depth cue, may affect the user's view of the augmented world. If focus depth is not adjusted properly, it may result in vision-based difficulties and reduce speed, accuracy, and comfort while using an augmented reality display. Thus, the second goal of this thesis was to study the effect of focus depth on task performance in augmented reality systems.

In augmented reality environments, real-world and virtual information are found at different distances from the user. To focus at different depths, the user's eye needs to accommodate and converge, which may strain the eye and degrade performance on tasks. However, no research in augmented reality has explored this issue. Hence, the third goal of this thesis was to determine if distance of virtual information from the user impacts task performance.

To accomplish these goals, a 3x3x3 within subjects design was used. The experimental task for the study required the user to repeatedly switch eye focus between the virtual text and real-world text. A monocular see-through head- mounted display was used for this research.

Results of this study revealed that switching between real-world and virtual information in augmented reality is extremely difficult when information is displayed at optical infinity. Virtual information displayed at optical infinity may be unsuitable for tasks of the nature used in this research. There was no impact of focus depth on user task performance and hence it is preliminarily recommended that manufacturers of head-mounted displays may only need to make fixed focus depth displays; this clearly merits additional intensive research. Further, user task performance was better when focus depth, virtual information, and real-world information were all at the same distance from the user as compared to conditions when they were mismatched. Based on this result we recommend presenting virtual information at the same distance as real-world information of interest.