This thesis aimed to compare self-reported and measured hearing loss by pure-tone audiometry and to determine what factors were associated with dietary intake, hearing loss and hearing-aid uptake and use in older people. This thesis analysed data from two large cohort studies- the Caerphilly Prospective Study and the Northern Ireland Cohort for the Longitudinal Study of Ageing. The main methods involved dietary pattern (DP) analysis, statistical analysis and both quantitative and qualitative analysis of interviews. This thesis found low but significant correlations between self-reported and audiometric measures of hearing loss. Poor dental health was significantly associated with reduced appetite. Diet quality was lower in males, younger older adults, those who were unmarried, widow(er)s, those with lower education and those with a higher BML In general, healthy DPs were associated with a decreased risk of chronic conditions and may be associated with a lower risk of hearing loss, although further work is required to confirm these findings. Hearing loss was significantly associated with a greater risk of depression and loneliness. Being older, having more severe hearing loss and owning a hearing-aid for a longer period of time were associated with greater hearing-aid uptake and use. Qualitative analysis revealed three main themes; factors affecting hearing-aid use. attitudes towards hearing-aids and audiology service. Self-reported measures of hearing loss were found to be acceptable measures of hearing loss, but only when audiological assessment is not feasible. A wide range of factors can adversely affect dietary intake in older people. Further work is necessary to determine the effect of dietary assessment method on DP analysis and the effect of examining a priori and a posteriori methods on observed associations with morbidity risk. More information, follow-up support and scheduled reviews are essential to increase hearing-aid uptake and use in older people.

Poorly managed hearing loss can lead to cognitive decline, depression and reduced quality of life. Using a hearing aid can help but evidence suggests up to 40% of people who are fitted with a hearing aid do not use it. While there are many reported reasons for non-use, research suggests that audiologist behaviour in the fitting consultation could play a key role in supporting hearing aid use. Following a systematic review of interventions to improve hearing aid use, this research used the steps of the Behaviour Change Wheel to identify four audiologist behaviours that might influence hearing aid use. An observational study and structured interviews with audiologists using the COM-B model as a framework identified potential determinants of the target behaviours. The COM-B model describes how capability (C), opportunity (O) and motivation (M) combine and influence behaviour (B). This analysis was used to select intervention functions and behaviour change techniques likely to affect behaviour change in this context. The intervention functions of education, training, persuasion, coercion, environmental restructuring, modelling and enablement were selected and combined to develop the I-PLAN; a complex intervention combining prompts, information and a behaviour plan for hearing aid use. This is the first study to use the COM-B model and Behaviour Change Wheel to develop a complex intervention in the context of audiology. Use of the COM-B model to analyse patient and professional behaviour has facilitated a consideration of implementation at the development stage of intervention design. The systematic, theory-based development of the I-PLAN intervention will facilitate a thorough evaluation of its feasibility and effectiveness over the next phases of this work.

No description available.

Non-linear frequency compression (NLFC) hearing aids are frequency lowering devices that compress a signal into a reduced bandwidth in order to maximise use of residual hearing. Only a few published studies have investigated benefit from NLFC hearing aids. Outcomes vary considerably between studies although most show large differences across listeners. This highlights the need for identification of reliable predictors of benefit. Furthermore, little is known about the time course and magnitude of perceptual learning associated with the use of NLFC amplification. A better understanding of these issues could potentially lead to significant clinical benefit and was therefore the focus of the present study. Two preliminary experiments were conducted on a total of 27 listeners with normal hearing in order to investigate the effect of NLFC on categorical perception and the role of cognition on NLFC outcome. The findings were used to inform the development (particularly with regards to the selection of NLFC fitting parameters) of a longitudinal study of 12 experienced adult hearing aid users with moderate-to-severe high frequency hearing loss. Participants wore the hearing aids, with and without NLFC enabled, in an A-B-A design, for approximately 6-7 weeks in each condition. Speech recognition, in both quiet (nonsense syllables) and noise (nonsense syllables and sentences), was measured at the end of each trial period. It was also measured at several time points when frequency compression was enabled in order to investigate perceptual learning. The opportunity was taken to gather preliminary self-report data (Glasgow Hearing Aid Benefit Profile and Speech, Spatial and Qualities of Hearing Scale) in order to identify possible trends on which to base future research. The results demonstrate that mean benefit on the speech recognition measures was greater when frequency compression was enabled. 9 out of 12 listeners obtained higher scores on the majority of outcome measures. There was no obvious difference on self report measures. Upon initial exposure to NLFC, there was an increase in confusions of some high frequency phonemes, especially of /f/ and /θ/ with /s/ (in both quiet and in noise); however, these confusions were less frequent after 6 weeks of NLFC hearing aid use. Limited evidence of perceptual learning of speech in noise was observed. In agreement with the findings of previous studies, large individual differences in benefit were evident. The relation between sentence in noise recognition (with and without NLFC enabled) and a variety of audiological (high frequency hearing loss and presence of dead regions) and cognitive factors (performance in the reading span and trail making tests) was examined. Audiological factors were shown to be predictive both of speech in noise recognition and of additional benefit obtained from NLFC. Listeners with the greatest high frequency loss derived the most benefit from NLFC. Once the effect of hearing loss had been partialled out, no other predictor correlated significantly with benefit from NLFC. However, the results support previous findings that cognitive functioning is predictive of benefit without NLFC, but suggest that this is primarily due to the influence of executive function rather than working memory span. The novel findings of the study (particularly those relating to speech in noise perception, acclimatisation to NLFC, and predictors of benefit from amplification) may help influence clinical practice, in relation to the assessment of candidacy for NLFC hearing aids and subsequent counselling offered to device users.

Cochlear implant (CI) users struggle to understand speech in noise. They suffer from elevated hearing thresholds and, with practically no binaural unmasking, they rely heavily on better-ear listening and lip reading. Traditional measures of spatial release from masking (SRM) quantify the speech reception threshold (SRT) improvement due to the azimuthal separation of speech and interferers when directly facing the speech source. The Jelfs et al. (2011) model of SRM predicts substantial benefits of orienting the head away from the target speech. Audio-only and audio-visual (AV) SRTs in normally hearing (NH) listeners and CI users confirmed model predictions of speech-facing SRM and head-orientation benefit (HOB). The lip-reading benefit (LRB) was not disrupted by a modest 30° orientation. When attending to speech with a gradually diminishing speech-to-noise-ratio (SNR), CI users were found to make little spontaneous use of their available HOB. Following a simple instruction to explore their HOB, CI users immediately reached as much as 5 dB lower SNRs. AV speech presentation significantly inhibited head movements (it nearly eradicated CI users’ spontaneous head turns), but had a limited impact on the SNRs reached post-instruction, compared to audio-only presentation. NH listeners age-matched to our CI participants made more spontaneous head turns in the free-head experiment but were poorer than CI users at exploiting their HOB post-instruction, despite their exhibiting larger objective HOB. NH listeners’ and CI users’ LRB measured 3 and 5 dB, respectively. Our findings both dispel the erroneous beliefs held by CI professionals that facing the speech constitutes an optimal listening strategy (whether for lip-reading or to optimise the use of microphone directionality) and pave the way to obvious translational applications.

Otitis Media with Effusion (OME) is a common childhood condition leading to hearing loss, and its treatment with ventilation tubes (VTs) is one of the commonest surgical procedures. However, aetiology of OME is poorly understood, and its current treatment requires improvement as OME frequently recurs once VTs extrude. The first, clinical part of this thesis showed that 63.6% of children randomised to VT insertion in a clinical trial will require VTs again, and even with additional adenoidectomy the need for repeat surgery remains high. Although published national guidelines set out criteria for surgery, the multicentre study presented here showed that only 32.2% of children that had VTs met these criteria, and guidelines' publication had limited impact on clinical practice. The second, laboratory part of this thesis demonstrated the importance that bacteria and biofilms play in aetiology of OME, as live bacteria were demonstrated in 91.9% of middle ear effusions (using culture and confocal microscopy). Following from this, a Staphylococcus aureus biofilm model was developed, and used to show that biofilm eradication requires antibiotic (rifampicin and lindamycin) levels 1,000 times higher than those required to inhibit planktonic bacteria, over a period of 2-3 weeks. To achieve this in the middle ear, a local delivery strategy using biodegradable poly (Iactic-coglycolic acid) antibiotic pellets was proposed. Drug release from these pellets was investigated with High Performance Liquid Chromatography and Serial Plate Transfer Testing, which demonstrated that antibiotics can be released for up to 3 weeks. Importantly, the pellets were able to eradicate biofilms in the in vitro model. This thesis has shown that current OME treatment has significant deficiencies, but better understanding of OME pathogenesis raises the possibility of rational new therapeutic strategies. Biodegradable antibiotic pellets designed to eradicate OME biofilms may be a better future treatment that could improve the lives of countless children.

Hearing loss is a widespread condition that can substantially affect not only auditory functioning but also social functioning. Therefore, it is essential to demonstrate that auditory rehabilitation can improve social participation in individuals with hearing loss. However, currently, there is a lack of agreed-upon, gold-standard, hearing-specific outcome measures. Consequently, the primary aim of this research was to develop a high quality measure of hearing-related social participation restrictions for use in research and practice. To achieve this aim, four consecutive studies were carried out using best practice questionnaire design techniques. Study 1 generated content for the Social Participation Restrictions Questionnaire (SPaRQ) through semi-structured interviews with 25 adults with hearing loss and nine hearing healthcare professionals. Study 2 evaluated the content of the measure through a subject matter expert panel with 20 hearing healthcare professionals and cognitive interviews with 14 adults with hearing loss. Study 3 assessed the psychometric properties of the SPaRQ by applying Rasch analysis to data collected from 279 adults with hearing loss. Finally, Study 4 further assessed the psychometric properties of the SPaRQ by applying traditional psychometric analysis to data collected from a further 102 adults with hearing loss. This research led to the development of a 19-item questionnaire that measured two key elements: social behaviours (e.g. difficulties with social interactions) and social perceptions (e.g. feelings of isolation). There was strong evidence to support the measurement properties of SPaRQ, including construct validity, person separation reliability, and internal consistency. Furthermore, the response scale was statistically justified and respondent burden was minimal. Future research should examine additional measurement properties, such as responsiveness and cross-cultural validity. Also, the best practice techniques used in this research should be applied to other new and existing hearing-specific questionnaires to ensure that they meet the requisite standards for use in clinical trials and clinical practice.

This thesis describes the development of an optical device to assess the inflammatory state of the middle ear mucosa through the ear canal, after ventilation tube insertion in otitis media with effusion in children. An optical phantom of the middle ear was developed in order to allow repeatable experiments. The phantom consists of eardrum and mucosa while all other structures are neglected. The optical properties of the phantom were determined based on literature review and experiments on an animal model. The middle ear mucosa phantom is based on a polyester resin, with dyes added to introduce absorption and a titanium dioxide based white colour to introduce scattering. Four phantom are created to model healthy, intermediate, and diseased mucosa. Several approaches are taken for the eardrum phantom, either a grid glass diffuser or a resin phantom with scattering introduced by fibre glass is used. Middle ear inflammation affects the mucosa while the eardrum might not be affected. Hence, the mucosa must be assessed and signals resulting from the eardrum, blocking the direct light path, filtered, in order to reduce background signals. During literature research and preliminary experiments, multi-wavelength measurements were selected to assess the mucosa and confocal techniques to allow measurements through the eardrum. The tissue is illuminated with two wavelengths and the reflected signal analysed. Appropriate selection of the wavelengths at characteristic point of the absorption spectrum of blood allows assessment of the inflammation via the blood concentration in tissue. The confocal idea was adopted leading to the “anti-confocal” system, where a central stop replacing the pinhole rejects light from the plane in focus rather than rejecting all out of focus light. With the eardrum in focus and a stop radius larger than the confocal pinhole radius (r_stop=0.48mm), most light from the eardrum is rejected (reduced to 0.2%) while signal from the mucosa are still detected (reduced to 25.6%), according to simulations. Simulations of the anti-confocal system showed an increase of the signal level by a factor of 3.2 or a 1.5 times higher background rejection ratio (SBR) compared to the conventional confocal system, when keeping the respective other value constant. This advantage still holds and is even improved in some cases when increasing the scattering coefficient (from 11 up to 44mm-1), reducing the scattering anisotropy (from 0.99 to 0.6), changing the distance between eardrum and mucosa (0.5 to 8mm), inaccurate focus (up to 3mm out of focus), and changed NA (0.055-0.27). Further, best wavelengths for measurements of the blood concentration and thus inflammation of the mucosa have been determined in simulations to be 730 and 546nm. In the investigated range of wavelengths (500 to 940nm), the relation of near infra-red signal at 730nm to green reflection signal at 546nm gives the highest response to a change in the total blood level in tissue while showing a low response to changes in blood oxygenation. The anti-confocal system was built as bench-top system and characterised. Instead of using a physical stop, a CCD camera was used and anti-confocal filtering done during post-processing, by selecting certain pixel on the camera. Experimental results confirmed the simulations and showed an increased signal and easier use of the anti-confocal system compared to the confocal system as no exact focus is required. An anti-confocal stop with 0.48mm radius showed best performance, showing a high contrast and low variation during the measurement. Measurements were possible with increased scattering (simulated by the stronger scattering grid glass diffuser) and attenuation (simulated by absorbing dyes added to the resin eardrum phantom) of the eardrum, increased distance between eardrum and mucosa (2-6mm), defocus of the system, and altered orientation of the phantom surface (0-10deg) with differences in the mucosal blood level still detectable. But the measured inflammation index is influenced by the transmission properties of the eardrum. While the influence of absorption can be accounted for by confocal detection of the properties of the eardrum during the same measurement, improved signal processing and modelling of light propagation are necessary to account for changed scattering of the eardrum. Tests on the hand of healthy volunteers showed that the proposed system is able to detect a change in the concentration of haemoglobin of living tissue measured through an eardrum simulating scattering layer. The next steps are the improvement of signal processing to account for changes of the measured inflammation index due to scattering of the eardrum. Once this is achieved, the optical system can be minimised to allow measurements on the ear and pilot trials for evaluation and calibration of the system.

While cochlear implants (CIs) have transformed the lives of hundreds of thousands of profoundly deaf individuals worldwide, the ability of individual patients to understand speech through their CI varies widely. The longitudinal study reported in this thesis aimed to investigate the role of cortical function and plasticity in helping to predict and explain variability in individual CI outcome. Speech-evoked cortical activations, measured using functional near-infrared spectroscopy (fNIRS), and behavioural measures of speech perception were acquired in adult CI recipients before implantation through to six months after CI activation. As anticipated, cochlear implantation enabled the significant recovery of auditory speech perception over the first six months of CI use, yet individual performance varied widely across CI users. fNIRS enabled the measurement of speech-evoked cortical activations from bilateral superior temporal cortex (STC) that were free from CI-generated artefacts. Cortical activation to visual speech measured before implantation was able to significantly predict future CI outcome measured following six months of CI use. This pre-implant measure of brain activity provided unique predictive value above that of well-established clinical characteristics, including the age-at-onset and duration of deafness. When examining changes in cortical activation from before to after implantation, a greater increase in STC activation to visual speech was found to be related to better CI outcome. These visual-related changes also predicted changes in STC activation to auditory speech. These results highlight the importance of visual speech cues and coupling between the auditory and visual modalities during the recovery of auditory function with a CI. Together, the findings demonstrate the potential of fNIRS as a brain-imaging tool that is uniquely well-suited for use in cochlear implantation. Future applications of this technology could help to explain individual variability in CI success and to deliver more accurate clinical prognoses for CI candidates.

The intention of the research activity described in this thesis is to contribute to the dynamical theory of the cochlea of the human inner ear. The Science of Hearing, being disseminated in a wide range of frequently independent or unco-ordinated disciplines, is advancing far in the fields of subjective human acoustics, middle ear restorative surgery, medical diagnostic electro-encephalography and cochlear-nucleus-to-thalamus neural communications research. At the same time, exploitation, in auditory research, of the techniques and resources of modern engineering science, which may be particularly appropriately applied to analyses of the peripheral hearing system, has not been manifest to any great degree. It was therefore hoped that a first-principles engineering approach to the subject of cochlear action would demonstrate the need for a mathematical and quantitative type of analysis of the response of this key organ of hearing and also indicate the extent to which cochlear science is at present to be found in a state of disarray. The writer's principal thesis is that a considerably greater potential for discrimination of the frequencies and intensities of pure and complex tones is attributable to the mechanical action of the cochlea than is generally supposed. That thesis will be more fully proven (it is expected) when current research is considerably extended and improved to permit the computation of spatial arrays of cochlear hair cell cilia shearing force patterns and electrical responses. The studies reported herein are relevant and fundamental to this aim and are limited to considerations of the dynamical response of the cochlear partition as a whole. This research has included approximately equal parts of review, physical cochlear model experimentation and mathematical analysis. The first two chapters end sections of most of the other chapters concentrate on defining the system and reviewing the literature. Chapters 3 and 4 estimate the order and ranges of the physical properties of mass and stiffness of the scala media (or cochlear partition), these properties being essential to the subsequent design of both physical and mathematical models of the cochlea in Chapters 5 and 6 respectively. The final chapter adds to the comments in other chapters on the credibility of the physical constants previously deduced in the thesis and tested in the models, the performance of the models, the particular problems clearly requiring further research effort and the relevance of the work to a more complete comprehension of human auditory theory.