  The information provided to a person's visual system by extended reality (XR)
displays is not a veridical match to the information provided by the real
world. Due in part to graphical limitations in XR head-mounted displays (HMDs),
which vary by device, our perception of space may be altered. However, we do
not yet know which properties of virtual objects rendered by HMDs --
particularly augmented reality displays -- influence our ability to understand
space. In the current research, we evaluate how immersive graphics affect
spatial perception across three unique XR displays: virtual reality (VR), video
see-through augmented reality (VST AR), and optical see-through augmented
reality (OST AR). We manipulated the geometry of the presented objects as well
as the shading techniques for objects' cast shadows. Shape and shadow were
selected for evaluation as they play an important role in determining where an
object is in space by providing points of contact between an object and its
environment -- be it real or virtual. Our results suggest that a
non-photorealistic (NPR) shading technique, in this case for cast shadows, may
be used to improve depth perception by enhancing perceived surface contact in
XR. Further, the benefit of NPR graphics is more pronounced in AR than in VR
displays. One's perception of ground contact is influenced by an object's
shape, as well. However, the relationship between shape and surface contact
perception is more complicated.
