E. R. Hafter
E. R. Jensen
Dept. of Psychol., Univ. of California, Berkeley, CA 94720
Virtual auditory environments are generally created by filtering stimuli through head-related transfer functions that mimic reflections and resonances of the shoulders, head, and external ears, and then presenting the sounds through earphones. Here, a different approach has been adopted in which multiple loudspeakers are used in an anechoic chamber to create virtual sources and echoes in space. Individual digital filters are used to equalize the loudspeakers and the computer/interface system allows for creation of multiple virtual sources and echoic surfaces. The locations of sources and echoic surfaces can be roved from trial to trial over a wide range of distances and over the eight separate azimuths allowed by the apparatus. Spatial discrimination is measured with two-alternative forced choice psychophysics while, for localization, subjects use a laser pointer to indicate the directions of apparent sources. For wideband clicks (cf=4 kHz), these results show that the presence of single echoes increases spatial thresholds by a factor of about 2 across the range of source azimuths from 0(degrees) to 90(degrees). The pointing data show that apparent locations of the sources are moved toward those of the echoes by about 4(degrees) to 5(degrees), a result that is unaffected by the magnitudes of the source--echo separation in either azimuth (8(degrees) to 40(degrees)) or delay (1 to 30 ms). At longer delays, subjects sometimes report double images, one near the direction of the source and the other near that of the echo.
The panel members, which represent a broad spectrum of researchers and engineers in the field of acoustics, will discuss their views on the nature of virtual acoustic displays and what will be required to implement them in future systems that more accurately simulate real sound sources in real acoustic environments. Simulation and generation of spatial and nonspatial characteristics of acoustic objects will be considered, including prerequisites in both basic knowledge and engineering techniques for implementing such cues. For example, research in the area of auditory streaming and perceptual organization will be discussed as well as the relative merits of implementations based on sampling techniques versus physical modeling of environmental sounds. Other practical research issues, such as the need to develop realizable (real-time) room-modeling techniques and perceptually viable methods for the spatial and temporal interpolation of moving sources, will also be addressed.