Masking In Three-dimensional Auditory Displays II: Effects Of Spatial And Spectral Simil2irity

It has been suggested that three dimensional (3-D) auditory displays could enhance operator performance in a wide variety of applications, including sonar (Doll, Hanna, and Ruissotti, in press), auditory warnings in aircraft cockpits (Doll et al., Most of the anticipated applications of 3-D auditory dislplays involve simultaneous presentation of multiple signals from different directions. A potential problem is that signals that are sounded simultaneously or closely in time may mask one-another. The extent to which simultaneous sounds mask one-(another should depend both upon their spectral similarity and how closely their sources are positioned in space. It is well esta'blished that masking is greatly reduced when the masker and signal do not occupy the same critical band (e.g., Durlach & Colburn, 1978). Studies of free-field masking show that the effectiveness of a masker decreases as it is separated in space from the signal However, the extent to which spectral and spatial similarity trade-off in determining the detectability of signals i n 3-0 auditory displays is unknom. This information i.s needed to design effective 3-D displays. The purpose of this research was to deternine how the spectral and spatial similarity of signals arid naskers interact to determine the deteczability of s i p a i s in 3-D audicory displays. A tonal signal and a **notchedtg noise masker were presented from loudspeakers with various spatial separations (0, 20, and 40 degrees) in a free field (i.e. , a *treal*t 3-D auditory display). The loudspeakers were arranged in a horizontal circular arc 10 ft. from the listener at ear l e v e l. The spectral similarity of the masker and signal were manipulated by varying the low-pass cutoff of one noise band and the high-pass cutoff of another, independent noise band, equal in spectral level to the first. The noises were mixed to form notches of various widths centered on the signal frequency. Minimimum signal levels required for 79.4 percent correcr: uetection were measured using an adaptive, two-alternative forced choice procedure. The subject was instructed not to m v e the head, and the chin was positioned in a chin rest.