Academic journal article Human Factors

Spatial and Spectral Release from Masking in Three-Dimensional Auditory Displays

Academic journal article Human Factors

Spatial and Spectral Release from Masking in Three-Dimensional Auditory Displays

Article excerpt

The extent to which simultaneous sounds in three-dimensional (3D) auditory displays mask one another was examined as a function of their spectral proximity and spatial separation. A tonal signal of either 0.5 or 4 kHz was presented at 0 deg azimuth in the horizontal plane of the listener's head. Spectral proximity was varied by centering a notched-noise masker on the signal frequency and varying the notch width. The masker was presented at an azimuth of 0, 20, or 40 deg, and the listener's head was immobilized. Detection levels decreased with both masker notch width and spatial separation. Analysis of the results shows that spatial separation produces both a broadening of the band over which masking is effective and a decrease in the minimum signal-to-noise ratio needed to detect the signal at all notch widths. Both effects were greater at 0.5 kHz than at 4 kHz. Additional experiments showed that these mechanisms are disrupted when two maskers are positioned symmetrically around the signal and head. The results are interpreted in terms of the effects of spatial separation on binaural processing and the listener's ability to resolve the signal and masker in frequency.

INTRODUCTION

Researchers have suggested that three-dimensional (3D) auditory displays could enhance operator performance in a wide variety of applications, including sonar (Doll, Hanna, and Russotti, 1992), auditory warnings in aircraft cockpits (Calhoun, Janson, and Valencia, 1988; Calhoun, Valencia, and Furness, 1987; Doll, Gerth, Engelman, and Folds, 1986), telerobotics and telepresence control (Wenzel, Fisher, Wightman, and Foster, 1988), air traffic control displays (Wenzel, 1994), and aids for the blind (Loomis, Hebert, and Cicinelli, 1990). Most of the anticipated applications of 3D auditory displays involve simultaneous presentation of multiple signals from different directions. A potential problem is that signals sounded simultaneously or closely in time may mask one another.

The extent to which simultaneous sounds mask one another depends on both their spectral similarity and how closely their sources are positioned in space. It is well established that masking is greatly reduced when the masker and signal do not occupy the same critical band (see the review by Durlach and Colburn, 1978). In addition, studies of free-field masking show that the effectiveness of a masker decreases as it is separated in space from the signal (e.g., Ebata, Sone, and Nimura, 1967; Moter, 1964, cited in Durlach and Colburn, 1978; Saberi, Dostal, Sadralodabai, Bull, and Perrott, 1991). However, the extent to which spectral and spatial separation interact in determining the detectability of signals in 3D auditory displays is unknown. This information is needed to design effective 3D auditory displays.

Patterson and his colleagues (e.g., Patterson, 1974, Patterson and Moore, 1986) developed a model of the frequency resolution of the auditory system, called the auditory filter. They showed that it can be used to estimate the audibility of signals in noisy environments, such as aircraft cockpits (Patterson, 1982). The auditory filter, illustrated in Figure 1, is a pass band that describes the listener's ability to detect one sound in the presence of other sounds -- that is, the extent to which a signal of one frequency is masked by noise or other signals of neighboring frequencies. It is closely related to the critical band (for reviews, see Patterson and Moore, 1986; Scharf, 1970). As one might expect, masking is greatest (signal detection level the highest) when the masker energy falls in the auditory filter pass band that is centered on the signal frequency. The masker becomes less effective as it is moved away from the signal frequency.

The auditory filter and critical band are usually measured monaurally and therefore refer to monaural frequency selectivity. However, a number of investigators have measured the counterpart of the critical band binaurally. …

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