Review of Self-Motion in the Context of Hearing and Hearing Device Research

Speech Intelligibility in Reverberation is Reduced During Self-Rotation

Speech intelligibility in cocktail party situations has been traditionally studied for stationary sound sources and stationary participants. Here, speech intelligibility and behavior were investigated during active self-rotation of standing participants in a spatialized speech test. We investigated if people would rotate to improve speech intelligibility, and we asked if knowing the target location would be further beneficial. Target sentences randomly appeared at one of four possible locations: 0°, ± 90°, 180° relative to the participant's initial orientation on each trial, while speech-shaped noise was presented from the front (0°). Participants responded naturally with self-rotating motion. Target sentences were presented either without (Audio-only) or with a picture of an avatar (Audio-Visual). In a baseline (Static) condition, people were standing still without visual location cues. Participants' self-orientation undershot the target location and orientations were close to acoustically optimal. Participants oriented more often in an acoustically optimal way, and speech intelligibility was higher in the Audio-Visual than in the Audio-only condition for the lateral targets. The intelligibility of the individual words in Audio-Visual and Audio-only increased during self-rotation towards the rear target, but it was reduced for the lateral targets when compared to Static, which could be mostly, but not fully, attributed to changes in spatial unmasking. Speech intelligibility prediction based on a model of static spatial unmasking considering self-rotations overestimated the participant performance by 1.4 dB. The results suggest that speech intelligibility is reduced during self-rotation, and that visual cues of location help to achieve more optimal self-rotations and better speech intelligibility.

Changes in Orientation Behavior due to Extended High-Frequency (5 to 10 kHz) Spatial Cues

OBJECTIVES

Current hearing aids have a limited bandwidth, which limits the intelligibility and quality of their output, and inhibits their uptake. Recent advances in signal processing, as well as novel methods of transduction, allow for a greater useable frequency range. Previous studies have shown a benefit for this extended bandwidth in consonant recognition, talker-sex identification, and separating sound sources. To explore whether there would be any direct spatial benefits to extending bandwidth, we used a dynamic localization method in a realistic situation.

DESIGN

Twenty-eight adult participants with minimal hearing loss reoriented themselves as quickly and accurately as comfortable to a new, off-axis near-field talker continuing a story in a background of far-field talkers of the same overall level in a simulated large room with common building materials. All stimuli were low-pass filtered at either 5 or 10 kHz on each trial. To further simulate current hearing aids, participants wore microphones above the pinnae and insert earphones adjusted to provide a linear, zero-gain response.

RESULTS

Each individual trajectory was recorded with infra-red motion-tracking and analyzed for accuracy, duration, start time, peak velocity, peak velocity time, complexity, reversals, and misorientations. Results across listeners showed a significant increase in peak velocity and significant decrease in start and peak velocity time with greater (10 kHz) bandwidth.

CONCLUSIONS

These earlier, swifter orientations demonstrate spatial benefits beyond static localization accuracy in plausible conditions; extended bandwidth without pinna cues provided more salient cues in a realistic mixture of talkers.

The Virtual Reality Lab: Realization and Application of Virtual Sound Environments

To assess perception with and performance of modern and future hearing devices with advanced adaptive signal processing capabilities, novel evaluation methods are required that go beyond already established methods. These novel methods will simulate to a certain extent the complexity and variability of acoustic conditions and acoustic communication styles in real life. This article discusses the current state and the perspectives of virtual reality technology use in the lab for designing complex audiovisual communication environments for hearing assessment and hearing device design and evaluation. In an effort to increase the ecological validity of lab experiments, that is, to increase the degree to which lab data reflect real-life hearing-related function, and to support the development of improved hearing-related procedures and interventions, this virtual reality lab marks a transition from conventional (audio-only) lab experiments to the field. The first part of the article introduces and discusses the notion of the communication loop as a theoretical basis for understanding the factors that are relevant for acoustic communication in real life. From this, requirements are derived that allow an assessment of the extent to which a virtual reality lab reflects these factors, and which may be used as a proxy for ecological validity. The most important factor of real-life communication identified is a closed communication loop among the actively behaving participants. The second part of the article gives an overview of the current developments towards a virtual reality lab at Oldenburg University that aims at interactive and reproducible testing of subjects with and without hearing devices in challenging communication conditions. The extent to which the virtual reality lab in its current state meets the requirements defined in the first part is discussed, along with its limitations and potential further developments. Finally, data are presented from a qualitative study that compared subject behavior and performance in two audiovisual environments presented in the virtual reality lab-a street and a cafeteria-with the corresponding field environments. The results show similarities and differences in subject behavior and performance between the lab and the field, indicating that the virtual reality lab in its current state marks a step towards more ecological validity in lab-based hearing and hearing device research, but requires further development towards higher levels of ecological validity.

The Quest for Ecological Validity in Hearing Science: What It Is, Why It Matters, and How to Advance It

Ecological validity is a relatively new concept in hearing science. It has been cited as relevant with increasing frequency in publications over the past 20 years, but without any formal conceptual basis or clear motive. The sixth Eriksholm Workshop was convened to develop a deeper understanding of the concept for the purpose of applying it in hearing research in a consistent and productive manner. Inspired by relevant debate within the field of psychology, and taking into account the World Health Organization's International Classification of Functioning, Disability, and Health framework, the attendees at the workshop reached a consensus on the following definition: "In hearing science, ecological validity refers to the degree to which research findings reflect real-life hearing-related function, activity, or participation." Four broad purposes for striving for greater ecological validity in hearing research were determined: A (Understanding) better understanding the role of hearing in everyday life; B (Development) supporting the development of improved procedures and interventions; C (Assessment) facilitating improved methods for assessing and predicting ability to accomplish real-world tasks; and D (Integration and Individualization) enabling more integrated and individualized care. Discussions considered the effects of variables and phenomena commonly present in hearing-related research on the level of ecological validity of outcomes, supported by examples from a few selected outcome domains and for different types of studies. Illustrated with examples, potential strategies were offered for promoting a high level of ecological validity in a study and for how to evaluate the level of ecological validity of a study. Areas in particular that could benefit from more research to advance ecological validity in hearing science include: (1) understanding the processes of hearing and communication in everyday listening situations, and specifically the factors that make listening difficult in everyday situations; (2) developing new test paradigms that include more than one person (e.g., to encompass the interactive nature of everyday communication) and that are integrative of other factors that interact with hearing in real-life function; (3) integrating new and emerging technologies (e.g., virtual reality) with established test methods; and (4) identifying the key variables and phenomena affecting the level of ecological validity to develop verifiable ways to increase ecological validity and derive a set of benchmarks to strive for.

Objective Assessment of Speech Intelligibility in Crowded Public Spaces

The objective of this study was to obtain a normative database of speech intelligibility data for young normal-hearing listeners communicating in public spaces. A total of 174 listeners participated in an interactive speech intelligibility task that required four-person groups to conduct a live version of the Modified Rhyme Test in noisy public spaces. The public spaces tested included a college library, a college cafeteria, a casual dining restaurant during lunch hour, and a crowded bar during happy hour. At the start of each trial, one of the participants was randomly selected as the talker, and a tablet computer was used to prompt them to say a word aloud from the Modified Rhyme Test. Then, the other three participants were required to select this word from one of six rhyming alternatives displayed on three other tablet computers. The tablet computers were also used to record the SPL at each listener location during and after the interval where the target talker was speaking. These SPL measurements were used to estimate the signal-to-noise ratio (SNR) in each trial of the experiment. As expected, the results show that speech intelligibility decreases, response time increases, and perceived difficulty increases as the background noise level increases. There was also a systematic decrease in SNR with increasing background noise, with SNR decreasing 0.44 dB for every 1 dB increase in ambient noise level above 60 dB. Overall, the results of this study have demonstrated how low-cost tablet computer-based data collection systems can be used to collect live-talker speech intelligibility data in real-world environments. We believe these techniques could be adapted for use in future studies focused on obtaining ecologically valid assessments of the effects of age, hearing impairment, amplification, and other factors on speech intelligibility performance in real-world environments.