Virtual objects in augmented reality (AR) often appear to float atop real world surfaces, which makes it difficult to determine where they are positioned in space. This is problematic as many applications for AR require accurate spatial perception. In the current study, we examine how the way we render cast shadows-which act as an important monocular depth cue for creating a sense of contact between an object and the surface beneath it-impacts spatial perception. Over two experiments, we evaluate people's sense of surface contact given both traditional and non-traditional shadow shading methods in optical see-through augmented reality (OST AR), video see-through augmented reality (VST AR), and virtual reality (VR) head-mounted displays. Our results provide evidence that nontraditional shading techniques for rendering shadows in AR displays may enhance the accuracy of one's perception of surface contact. This finding implies a possible tradeoff between photorealism and accuracy of depth perception, especially in OST AR displays. However, it also supports the use of more stylized graphics like non-traditional cast shadows to improve perception and interaction in AR applications.

Augmented reality (AR) technologies have the potential to provide individuals with unique training and visualizations, but the effectiveness of these applications may be influenced by users' perceptions of the distance to AR objects. Perceived distances to AR objects may be biased if these objects do not appear to make contact with the ground plane. The current work compared distance judgments of AR targets presented on the ground versus off the ground when no additional AR depth cues, such as shadows, were available to denote ground contact. We predicted that without additional information for height off the ground, observers would perceive the off-ground objects as placed on the ground, but at farther distances. Furthermore, this bias should be exaggerated when targets were viewed with one eye rather than two. In our experiment, participants judged the absolute egocentric distance to various cubes presented on or off the ground with an action-based measure, blind walking. We found that observers walked farther for off-ground AR objects and that this effect was exaggerated when participants viewed off-ground objects with monocular vision compared to binocular vision. However, we also found that the restriction of binocular cues influenced participants' distance judgments for on-ground AR objects. Our results suggest that distances to off-ground AR objects are perceived differently than on-ground AR objects and that the elimination of binocular cues further influences how users perceive these distances.

It is an open question as to whether people perceive and act in augmented reality environments in the same way that they do in real environments. The current work investigated participants' judgments of whether or not they could act on an obstacle portrayed with augmented reality. Specifically, we presented gaps of varying widths and depths to participants in augmented reality using the Microsoft HoloLens. We asked users to indicate whether or not they believed that they could step across the virtual gaps given their widths and depths. Averaging across changes in width and depth, users generally underestimated their abilities to cross gaps. However, this underestimation was significantly greater when the gaps were deep. Thus, our findings suggest that users in augmented reality respond with more conservative judgments when presented with risky stimuli-a response that mimics real world behavior. Their altered reactions to deeper gaps may provide early evidence for augmented reality's capacity to evoke a sense of realism or immersion and its use in evaluating perception and action.

The utility of mediated environments increases when environmental scale (size and distance) is perceived accurately. We present the use of perceived affordances---judgments of action capabilities---as an objective way to assess space perception in an augmented reality (AR) environment. The current study extends the previous use of this methodology in virtual reality (VR) to AR. We tested two locomotion-based affordance tasks. In the first experiment, observers judged whether they could pass through a virtual aperture presented at different widths and distances, and also judged the distance to the aperture. In the second experiment, observers judged whether they could step over a virtual gap on the ground. In both experiments, the virtual objects were displayed with the HoloLens in a real laboratory environment. We demonstrate that affordances for passing through and perceived distance to the aperture are similar in AR to those measured in the real world, but that judgments of gap-crossing in AR were underestimated. These differences across two affordances may result from the different spatial characteristics of the virtual objects (on the ground versus extending off the ground).