An Extended Binaural Real-Time Auralization System With an Interface to Research Hearing Aids for Experiments on Subjects With Hearing Loss

The impact of head-related impulse response delay treatment strategy on psychoacoustic cue reconstruction errors from virtual loudspeaker arrays

Known errors exist in loudspeaker array processing techniques, often degrading source localization and timbre. The goal of the present study was to use virtual loudspeaker arrays to investigate how treatment of the interaural time delay (ITD) cue from each loudspeaker impacts these errors. Virtual loudspeaker arrays rendered over headphones using head-related impulse responses (HRIRs) allow flexible control of array size. Here, three HRIR delay treatment strategies were evaluated using minimum-phase loudspeaker HRIRs: reapplying the original HRIR delays, applying the relative ITD to the contralateral ear, or separately applying the HRIR delays prior to virtual array processing. Seven array sizes were simulated, and panning techniques were used to estimate HRIRs from 3000 directions using higher-order Ambisonics, vector-base amplitude panning, and the closest loudspeaker technique. Compared to a traditional, physical array, the prior HRIR delay treatment strategy produced similar errors with a 95% reduction in the required array size. When compared to direct spherical harmonic (SH) fitting of head-related transfer functions (HRTFs), the prior delays strategy reduced errors in reconstruction accuracy of timbral and directional psychoacoustic cues. This result suggests that delay optimization can greatly reduce the number of virtual loudspeakers required for accurate rendering of acoustic scenes without SH-based HRTF representation.

A Compact Two-Loudspeaker Virtual Sound Reproduction System for Clinical Testing of Spatial Hearing With Hearing-Assistive Devices

Exciting developments in hearing aid and cochlear implant technology for linking signal processing across the ears have improved spatial hearing outcomes. This has resulted in an increased emphasis on clinical assessment of the spatial hearing abilities of hearing-assistive device users. Effective assessment of spatial hearing currently requires a large and costly loudspeaker array system, housed in a heavily acoustically treated testing room. This imposes economic and logistical constraints that limit proliferation of array systems, particularly in developing nations. Despite their size and cost, the ability of current clinical array systems to reproduce realistic spatial sound fields is limited, which substantially reduces the range of realistic acoustic scenes that can be used for diagnostic testing. We propose an alternative low-cost, compact virtual acoustics system with just two loudspeakers. This system uses crosstalk cancelation to reproduce pressure signals at the device microphones that match those for real-world sound sources. Furthermore, in contrast to clinical array systems, the system can adapt to different room acoustics, removing the requirement for a heavily acoustically treated testing environment. We conducted a proof-of-concept study in two stages: in the first, we evaluated the physical performance of the system for a stationary listener in anechoic conditions and in a small audiological testing booth with moderate acoustic treatment. To do this, a head and torso simulator was fitted with specially adapted hearing-assistive devices that allowed direct access to the microphone signals. These microphone signals were compared for real and virtual sound sources at numerous source locations. In the second stage, we quantified the system’s robustness to head rotations with and without the system adapting for head position. In the stationary case, the system was found to be highly effective at reproducing signals, such as speech, at all tested source locations. When head rotation was added, it performed well for rotations of up to 2°, even without adapting. However, performance improved markedly for larger rotations when the system adapted. These findings suggest that a compact, low-cost virtual acoustics system can give wider access to advanced and ecologically valid audiological testing, which could substantially improve clinical assessment of hearing-assistive device users.

Spatial release from masking in reverberation for school-age children

Understanding speech in noisy environments, such as classrooms, is a challenge for children. When a spatial separation is introduced between the target and masker, as compared to when both are co-located, children demonstrate intelligibility improvement of the target speech. Such intelligibility improvement is known as spatial release from masking (SRM). In most reverberant environments, binaural cues associated with the spatial separation are distorted; the extent to which such distortion will affect children's SRM is unknown. Two virtual acoustic environments with reverberation times between 0.4 s and 1.1 s were compared. SRM was measured using a spatial separation with symmetrically displaced maskers to maximize access to binaural cues. The role of informational masking in modulating SRM was investigated through voice similarity between the target and masker. Results showed that, contradictory to previous developmental findings on free-field SRM, children's SRM in reverberation has not yet reached maturity in the 7-12 years age range. When reducing reverberation, an SRM improvement was seen in adults but not in children. Our findings suggest that, even though school-age children have access to binaural cues that are distorted in reverberation, they demonstrate immature use of such cues for speech-in-noise perception, even in mild reverberation.

Ecological Validity of Immersive Virtual Reality (IVR) Techniques for the Perception of Urban Sound Environments

Immersive Virtual Reality (IVR) is a simulated technology used to deliver multisensory information to people under different environmental conditions. When IVR is generally applied in urban planning and soundscape research, it reveals attractive possibilities for the assessment of urban sound environments with higher immersion for human participation. In virtual sound environments, various topics and measures are designed to collect subjective responses from participants under simulated laboratory conditions. Soundscape or noise assessment studies during virtual experiences adopt an evaluation approach similar to in situ methods. This paper aims to review the approaches that are utilized to assess the ecological validity of IVR for the perception of urban sound environments and the necessary technologies during audio–visual reproduction to establish a dynamic IVR experience that ensures ecological validity. The review shows that, through the use of laboratory tests including subjective response surveys, cognitive performance tests and physiological responses, the ecological validity of IVR can be assessed for the perception of urban sound environments. The reproduction system with head-tracking functions synchronizing spatial audio and visual stimuli (e.g., head-mounted displays (HMDs) with first-order Ambisonics (FOA)-tracked binaural playback) represents the prevailing trend to achieve high ecological validity. These studies potentially contribute to the outcomes of a normalized evaluation framework for subjective soundscape and noise assessments in virtual environments.

Localization Performance in a Binaural Real-Time Auralization System Extended to Research Hearing Aids

Auralization systems for auditory research should ideally be validated by perceptual experiments, as well as objective measures. This study employed perceptual tests to evaluate a recently proposed binaural real-time auralization system for hearing aid (HA) users. The dynamic localization of real sound sources was compared with that of virtualized ones, reproduced binaurally over headphones, loudspeakers with crosstalk cancellation (CTC) filters, research HAs, or combined via loudspeakers with CTC filters and research HAs under free-field conditions. System-inherent properties affecting localization cues were identified and their effects on overall horizontal localization, reversal rates, and angular error metrics were assessed. The general localization performance in combined reproduction was found to fall between what was measured for loudspeakers with CTC filters and research HAs alone. Reproduction via research HAs alone resulted in the highest reversal rates and angular errors. While combined reproduction helped decrease the reversal rates, no significant effect was observed on the angular error metrics. However, combined reproduction resulted in the same overall horizontal source localization performance as measured for real sound sources, while improving localization compared with reproduction over research HAs alone. Collectively, the results with respect to combined reproduction can be considered a performance indicator for future experiments involving HA users.

Sound Externalization: A Review of Recent Research

Sound externalization, or the perception that a sound source is outside of the head, is an intriguing phenomenon that has long interested psychoacousticians. While previous reviews are available, the past few decades have produced a substantial amount of new data.In this review, we aim to synthesize those data and to summarize advances in our understanding of the phenomenon. We also discuss issues related to the definition and measurement of sound externalization and describe quantitative approaches that have been taken to predict the outcomes of externalization experiments. Last, sound externalization is of practical importance for many kinds of hearing technologies. Here, we touch on two examples, discussing the role of sound externalization in augmented/virtual reality systems and bringing attention to the somewhat overlooked issue of sound externalization in wearers of hearing aids.

fNIRS Assessment of Speech Comprehension in Children with Normal Hearing and Children with Hearing Aids in Virtual Acoustic Environments: Pilot Data and Practical Recommendations

The integration of virtual acoustic environments (VAEs) with functional near-infrared spectroscopy (fNIRS) offers novel avenues to investigate behavioral and neural processes of speech-in-noise (SIN) comprehension in complex auditory scenes. Particularly in children with hearing aids (HAs), the combined application might offer new insights into the neural mechanism of SIN perception in simulated real-life acoustic scenarios. Here, we present first pilot data from six children with normal hearing (NH) and three children with bilateral HAs to explore the potential applicability of this novel approach. Children with NH received a speech recognition benefit from low room reverberation and target-distractors' spatial separation, particularly when the pitch of the target and the distractors was similar. On the neural level, the left inferior frontal gyrus appeared to support SIN comprehension during effortful listening. Children with HAs showed decreased SIN perception across conditions. The VAE-fNIRS approach is critically compared to traditional SIN assessments. Although the current study shows that feasibility still needs to be improved, the combined application potentially offers a promising tool to investigate novel research questions in simulated real-life listening. Future modified VAE-fNIRS applications are warranted to replicate the current findings and to validate its application in research and clinical settings.

Spatial Release From Masking Under Different Reverberant Conditions in Young and Elderly Subjects: Effect of Moving or Stationary Maskers at Circular and Radial Conditions

Purpose Normal-hearing and hard-of-hearing listeners suffer from reduced speech intelligibility in noisy and reverberant environments. Although daily listening environments are in constant motion, most researchers have only studied speech-in-noise perception for stationary masker locations. The aim of this study was to investigate the spatial release from masking (SRM) of circularly and radially moving maskers under different room acoustic conditions for young and elderly subjects. Method Twelve young subjects with normal hearing and 12 elderly subjects with normal hearing or mild hearing loss were tested. Several different room acoustic conditions were simulated and reproduced via headphones using binaural synthesis. The target speech stream consisted of German digit triplets, and masker stream consisted of quasistationary noise with matched long-term averaged speech spectra. During the experiment, the position of the masker was changed to be in different stationary positions, or varied continuously. In the latter case, it was moved either on a circular trajectory spanning a 90° azimuth angle or on a radial trajectory linearly increasing the distance to the receiver from 0.5 m to 1.8 m. Absorption characteristics of the virtual room's surfaces were changed, recreating an anechoic room, a treated room with mean reverberation times (RT60) = 0.48 s, and an untreated room with mean RT60 = 1.26 s. Results For the circular condition, a significant difference was found between moving and stationary maskers, F(4, 44) = 20.91, p < .001, with a bigger SRM for stationary maskers than moving masker conditions. Also, both age groups displayed a significant decrease in SRM over the reverberation conditions: F(2, 22) = 12.24, p < .001. For the radial condition, both age groups showed a significant decrease in SRM over the reverberation conditions, F(2, 22) = 13.62, p < .001, as well as the moving and stationary masker conditions, F(8, 88) = 29.23, p < .001. In general, the SRM of a moving masker decreased when the reverberation increased, especially for elderly subjects. Conclusions A radially moving masker led to improved SRM in an anechoic environment for both age groups, whereas a circularly moving masker caused degraded SRM, especially for elderly subjects in the highly reverberant environment. Supplemental Material https://doi.org/10.23641/asha.9795371.