Validation of a Virtual Sound Environment System for Testing Hearing Aids

Abstract

SummaryIn the development process of modern hearing aids, test scenarios that reproduce natural acoustic scenes have become increasingly important in recent years for the evaluation of new signal processing algorithms. To achieve high ecological validity, such scenarios should include components like reverberation, background noise, and multiple interfering talkers. Loudspeaker-based sound field reproduction techniques, such as higher-order Ambisonics, allow for the simulation of such complex sound environments and can be used for realistic listening experiments with hearing aids. However, to successfully employ such systems, it is crucial to know how experimental results from a virtual environment translate to the corresponding real environment. In this study, speech reception thresholds (SRTs) were measured with normal-hearing listeners wearing hearing aids, both in a real room and in a simulation of that room auralized via a spherical array of 29 loudspeakers, using either Ambisonics or a nearest loudspeaker method. The benefit from a static beamforming algorithm was considered in comparison to a hearing aid setting with omnidirectional microphones. The measured SRTs were about 2-4 dB higher, and the benefit from the beamformer setting was, on average, about 1.5 dB smaller in the virtual room than in the real room. These differences resulted from a more diffuse sound field in the virtual room as indicated by differences in measured directivity patterns for the hearing aids and interaural cross-correlation coefficients. Overall, the considered VSE system may represent a valuable tool for testing the effects of hearing-aid signal processing on physical and behavioural outcome measures in realistic acoustic environments.

Listening through hearing aids affects spatial perception and speech intelligibility in normal-hearing listeners

“…A number of studies have explored the possibility that hearing loss impedes spatial perception, e.g., in terms of localization ability (Noble et al , 1994; Lorenzi et al , 1999; Best et al , 2010; Best et al , 2011; Hassager et al , 2017) or ITD discrimination performance (e.g., Durlach et al , 1981; Strelcyk and Dau, 2009; Spencer et al , 2016). Furthermore, several studies have suggested that HAs can disrupt the auditory cues involved in spatial perception (Van den Bogaert et al , 2006; Wiggins and Seeber, 2012; Akeroyd and Whitmer, 2016; Cubick and Dau, 2016; Hassager et al , 2017). For example, Hassager et al (2017) showed that localization accuracy in a moderately reverberant room was substantially degraded as a consequence of fast-acting dynamic-range compression in bilateral HAs, independent of whether the compression was synchronized across the two HAs or not.…”

“…However, the effects of these distortions on speech intelligibility were not investigated in that study. Cubick and Dau (2016) measured speech reception thresholds (SRTs) in normal-hearing listeners using omnidirectional regular production HAs with linear (i.e., level-independent) amplification. They found that amplification (relative to no amplification) increased SRTs by about 4 dB, i.e., degraded speech intelligibility, in a setting with spatially distributed sources inside a classroom.…”

“…Inspired by Cubick and Dau (2016), the current study investigated the potential effect of degraded spatial cues when listening through HAs on SRTs in spatially separated masking conditions. To do so, a very basic amplification scheme was used, that included linear gain and no sophisticated signal processing.…”

“…This choice was made such that the only distortion of the incoming sound would be caused by the position of the microphones above the ears, which modifies the spatial cues compared to natural listening. This enabled a test of whether spatial distortions and elevated SRTs as in Cubick and Dau (2016) would be found even in the absence of effects related to specific signal processing schemes. Furthermore, it was investigated to what extent HAs affect the amount of IM (versus EM) in a complex acoustic setting with several interferers.…”

“…On the other hand, if the HAs were to distort the spatial information enough to disrupt the listeners' ability to perceptually separate the target and the interferer signals, then this might reduce the spatial release from IM and the impact would primarily be seen in the case of speech interferers. To characterize the influence of HAs on the spatial perception of the acoustic scenes in the horizontal plane, the same listeners were also asked to draw sketches to indicate the position and spatial distribution of the sound images they perceived using a method inspired by earlier studies (Plenge, 1972; Blauert and Lindemann, 1986; Cubick and Dau, 2016). …”