The quality of realism in virtual environments (VEs) is typically considered to be a function of visual and audio fidelity mutually exclusive of each other. However, the VE participant, being human, is multimodal by nature. Therefore, in order to validate more accurately the levels of auditory and visual fidelity that are required in a virtual environment, a better understanding is needed of the intersensory or crossmodal effects between the auditory and visual sense modalities. To identify whether any pertinent auditory-visual cross-modal perception phenomena exist, 108 subjects participated in three experiments which were completely automated using HTML, Java, and JavaScript programming languages. Visual and auditory display quality perceptions were measured intraand intermodally by manipulating the pixel resolution of the visual display and Gaussian white noise level, and by manipulating the sampling frequency of the auditory display and Gaussian white noise level. Statistically significant results indicate that high-quality auditory displays coupled with highquality visual displays increase the quality perception of the visual displays relative to the evaluation of the visual display alone, and that low-quality auditory displays coupled with high-quality visual displays decrease the quality perception of the auditory displays relative to the evaluation of the auditory display alone. These findings strongly suggest that the quality of realism in VEs must be a function of both auditory and visual display fidelities inclusive of each other.

This paper describes the implementation of the sound system used to generate aural cues for use in the distributed virtual environment of NPSNET. This sound system is called the NPSNET-3D Sound Server. It is a MIDI-based loudspeaker system consisting of commercial, off-the-shelf equipment. This sound system currently generates 2-D aural cues via four speakers, but is designed for the potential generation of 3-D aural cues via a cube con®guration of eight speakers.