Abstract
The ability to localize a sound source is very important in our daily life, specifically to analyze auditory scenes in complex acoustic environments. The concept of minimum audible angle (MAA), which is defined as the smallest detectable difference between the incident directions of two sound sources, has been widely used in the research fields of auditory perception to measure localization ability. Measuring MAAs usually involves a reference sound source and either a large number of loudspeakers or a movable sound source in order to reproduce sound sources at a large number of predefined incident directions. However, existing MAA test systems are often cumbersome because they require a large number of loudspeakers or a mechanical rail slide and thus are expensive and inconvenient to use. This study investigates a novel MAA test method using virtual sound source synthesis and avoiding the problems with traditional methods. We compare the perceptual localization acuity of sound sources in two experimental designs: using the virtual presentation and real sound sources. The virtual sound source is reproduced through a pair of loudspeakers weighted by vector-based amplitude panning (VBAP). Results show that the average measured MAA at 0° azimuth is 1.1° and the average measured MAA at 90° azimuth is 3.1° in a virtual acoustic system, meanwhile the average measured MAA at 0° azimuth is about 1.2° and the average measured MAA at 90° azimuth is 3.3° when using the real sound sources. The measurements of the two methods have no significant difference. We conclude that the proposed MAA test system is a suitable alternative to more complicated and expensive setups.
Highlights
The smallest perceptually detectable difference between the azimuths of two sound sources is called the minimum audible angle (MAA) (Mills, 1958)
In the frontal MAA measurement experiment, we assume that participants have an average of about 50% correct at 0◦ and almost achieve 100% accuracy at the angular separation of 8◦, and in the lateral MAA measurement experiment, we assume that participants have an average of about 50% correct at 0◦ and achieve 100% accuracy at the angular separation of 15◦
We found that the performance in the frontal MAA measurement experiment is not statistically correlated with the performance in the lateral experiment (r = 0.02, p > 0.05 in baseline method, r = 0.01, p > 0.05 in vector-based amplitude panning (VBAP) method)
Summary
The smallest perceptually detectable difference between the azimuths of two sound sources is called the minimum audible angle (MAA) (Mills, 1958). In 1958, Mills proposed the concept of MAA to measure perceptional auditory spatial acuity and since the MAA has been used in many studies on sound localization and auditory perception. The MAA test was used to investigate the precedence effect in sound localization (Litovsky and Macmillan, 1994) or to measure the sound localization acuity of children with cochlear implants (Saberi et al, 1991; Litovsky et al, 2006; Tyler et al, 2010). Sound source localization is important for auditory scene analysis (McAdams, 1984, 1993; Tyler et al, 2002; Grieco-Calub and Litovsky, 2010; Kerber and Seeber, 2012). It would be preferable to have a controlled method to render virtual stimuli at any angle when measuring the MAA at any desired incident direction
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