The primary concern of this paper is whether the utility of audio spatialization, as opposed to the fidelity of audio spatialization, impacts presence. An experiment is reported that investigates the presence-performance relationship by decoupling spatial audio fidelity (realism) from task performance by varying the spatial fidelity of the audio independently of its relevance to performance on the search task that subjects were to perform. This was achieved by having conditions in which subjects searched for a music-playing radio (an active sound source) and having conditions in which the playing radio would be stationary (a passive sound source) while subjects searched for some other object. Independent of this, the music emitted by the radio would be either fully spatialized or directional but nonattenuated.Findings include that for subjects searching for the active sound source, being supplied only nonattenuated audio was detrimental to performance. Even so, this group of subjects consistently had the largest increase in presence scores over the baseline experiment. Further, the Witmer and Singer (1998) presence questionnaire was more sensitive to whether the audio source was active or not, while the presence questionnaire used by Slater and coworkers (see Tromp et al., 1998) was more sensitive to whether audio was fully spatialized or not. Finally, having the sound source active positively impacts the assessment of the audio while negatively impacting subjects' assessment of the visuals.

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In this paper, occlusion testing in very large virtual environments is discussed from two perspectives: a theoretical one, discussing occlusion culling in relation to detail elision (level of detail), and a practical one, relating to an adaptive occlusion-culling algorithm developed in this paper. The theoretical perspective formally demonstrates the efficiency of detail elision in the face of real-world-like environments. It further shows the utility of using detail elision not only to lower the triangle count of individual objects but also to lower the load on the scene graph traversal algorithm. Finally, the results indicate that, even in open environments, one needs occlusion culling and that approaches based on choosing only a few good (convex) occluders are insufficient in this case. Practically, the theoretical perspective is reflected in the development of an occlusion-culling algorithm based on a marriage of the frustum-slicing approach to view frustum culling and hierarchical occlusion maps (HOMs). The resulting algorithm is much simpler than the original HOM algorithm, requires little pre-processing, and integrates detail elision with the occlusion-culling algorithm in a natural way. The approach is well suited for use with large, complex models with a long mean free line of sight (“the great outdoors”), models for which it is not feasible to construct, or search, a database of occluders to be rendered in each frame. The algorithm is tested for such large models, and results show that frame rates tend to converge as the geometrical complexity of the model increases.

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