Evaluation of different signal processing options in unilateral and bilateral Cochlear Freedom recipients using R-Space background noise

Understanding speech in the presence of noise is a difficult task for cochlear implant patients. This study examines the real-world effectiveness of different signal processing approaches available in the Cochlear Nucleus Freedom device to enhance speech perception in noise for cochlear implant recipients

Improvement of Speech Perception for Hearing-Impaired Listeners

Hearing impairment is becoming a prevalent health problem affecting 5% of world adult populations. Hearing aids and cochlear implant already play an essential role in helping patients over decades, but there are still several open problems that prevent them from providing the maximum benefits. Financial and discomfort reasons lead to only one of four patients choose to use hearing aids; Cochlear implant users always have trouble in understanding speech in a noisy environment. In this dissertation, we addressed the hearing aids limitations by proposing a new hearing aid signal processing system named Open-source Self-fitting Hearing Aids System (OS SF hearing aids). The proposed hearing aids system adopted the state-of-art digital signal processing technologies, combined with accurate hearing assessment and machine learning based self-fitting algorithm to further improve the speech perception and comfort for hearing aids users. Informal testing with hearing-impaired listeners showed that the testing results from the proposed system had less than 10 dB (by average) difference when compared with those results obtained from clinical audiometer. In addition, Sixteen-channel filter banks with adaptive differential microphone array provides up to six-dB SNR improvement in the noisy environment. Machine-learning based self-fitting algorithm provides more suitable hearing aids settings. To maximize cochlear implant users’ speech understanding in noise, the sequential (S) and parallel (P) coding strategies were proposed by integrating high-rate desynchronized pulse trains (DPT) in the continuous interleaved sampling (CIS) strategy. Ten participants with severe hearing loss participated in the two rounds cochlear implants testing. The testing results showed CIS-DPT-S strategy significantly improved (11%) the speech perception in background noise, while the CIS-DPT-P strategy had a significant improvement in both quiet (7%) and noisy (9%) environment

Modelling, Simulation and Data Analysis in Acoustical Problems

Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years

Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels

Development of a sensory substitution API

2018 Summer.Includes bibliographical references.Sensory substitution – or the practice of mapping information from one sensory modality to another – has been shown to be a viable technique for non-invasive sensory replacement and augmentation. With the rise in popularity, ubiquity, and capability of mobile devices and wearable electronics, sensory substitution research has seen a resurgence in recent years. Due to the standard features of mobile/wearable electronics such as Bluetooth, multicore processing, and audio recording, these devices can be used to drive sensory substitution systems. Therefore, there exists a need for a flexible, extensible software package capable of performing the required real-time data processing for sensory substitution, on modern mobile devices. The primary contribution of this thesis is the development and release of an Open Source Application Programming Interface (API) capable of managing an audio stream from the source of sound to a sensory stimulus interface on the body. The API (named Tactile Waves) is written in the Java programming language and packaged as both a Java library (JAR) and Android library (AAR). The development and design of the library is presented, and its primary functions are explained. Implementation details for each primary function are discussed. Performance evaluation of all processing routines is performed to ensure real-time capability, and the results are summarized. Finally, future improvements to the library and additional applications of sensory substitution are proposed

Perception of speech, music and emotion by hearing-impaired listeners

The everyday tasks of perceiving speech, music and emotional expression via both of these media, are made much more difficult in the case of hearing impairment. Chiefly, this is because relevant acoustic cues are less clearly audible, owing to both hearing loss in itself, and the limitations of available hearing prostheses. This thesis focussed specifically on two such devices, the cochlear implant (CI) and the hearing aid (HA), and asks two overarching questions: how do users approach music and speech perception tasks, and how can performance be improved? The first part of the thesis considered auditory perception of emotion by CI users. In particular, the underlying mechanisms by which this population perform such tasks are poorly understood. This topic was addressed by a series of emotion discrimination experiments, featuring both normal-hearing (CI-simulated) participants and real CI users, in which listeners heard stimuli with processing designed to systematically attenuate different acoustic features. Additionally, a computational modelling approach was utilised in order to estimate participants' listening strategies, and whether or not these were optimal. It was shown that the acoustic features attended to by participants were a compromise of those generally better-preserved by the CI, and those particularly salient for each stimulus. In the latter half of the thesis, the nature of assessment of music perception by hearing-impaired listeners was considered. Speech perception has typically taken precedence in this domain which, it is argued, has left assessment of music perception relatively underdeveloped. This problem was addressed by the creation of a novel, psychoacoustical testing procedure, similar to those typically used with speech. This paradigm was evaluated via listening experiments with both HA users and CI-simulated listeners. In general, the results indicated that the measure produced both valid and reliable results, suggesting the suitability of the procedure as both a clinical and experimental tool. Lastly, the thesis considered the consequences of the various findings for both research and clinical practice, contextualising the results with reference to the primary research questions addressed, and thereby highlighting what there is left to discover

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

otorhinolaryngology; neurosciences; hearin