A biologically-inspired hearing aid

Summary This project proposes to design, build and evaluate a new design of biologically-inspired hearing aid in collaboration with a world-leading manufacturer (Phonak). The design is specifically targeted at improving the perception of speech in noisy environments. The process of tuning the aid will use computer models of patient hearing developed in the on-going Hearing Dummy Project at Essex University. A successful outcome should prepare the way for a new generation of hearing aid designs and major changes in dispensing practice. The most common complaint associated with hearing impairment is difficulty in understanding speech in noisy backgrounds at work and in pubs, restaurants and parties. Conventional hearing aids restore normal thresholds and offer more comfortable levels of sound. However, they are not successful in solving the problem of hearing speech in noise. Recent research has suggested that normal hearing is successful because it uses a process of instantaneous compression combined with other methods of input level regulation linked to the level of the background noise. In a recent computer-based study we have shown that the implementation of these biological processes can improve the recognition of speech in noisy backgrounds. In this project we shall design and build a hearing aid that uses these principles to aid the perception of speech in challenging situations. The project involves a software design study at Essex and a hardware implementation study by a manufacturer. Phonak AG, the hearing aid company, is strongly supportive of the proposal and will collaborate by addressing the hardware design issues and implementing the new principles as a working, wearable hearing aid. This proposal is associated with an on-going EPSRC-funded project that will provide facilities and patients for testing the new algorithm. Computer models of hearing will play an important role in the design process. We have developed a model of normal hearing that incorporates the biological principles of the acoustic reflex, instantaneous compression and efferent depression. The 'normal' model forms the basis of the new hearing aid design with a view to restoring effects that are missing in patients. Hearing impairment is typically characterised as an inability to hear quiet sounds but this may be too simplistic. For many people with a hearing impairment, automatic regulation of input level is also ineffective. We have simulated this in individualised computer models of a number of impaired listeners and shown that this replicates their psychometric data. By combining the hearing aid based on the 'normal' model with an 'impaired' model in a software harness it will be possible to identify the optimum settings of the hearing aid needed for a given patient to restore normal hearing in a speech recognition task. Our 'impaired' computer models are based on measurements made on an individual patient (like a tailor's dummy). Recent research in our laboratory has developed rapid patient evaluation methods that measure thresholds, tuning and compression. These measurements show substantial differences among patients who have similar audiograms and would be prescribed similar hearing aids. We have made detailed measurements of a number of patients and created computer models of their hearing. These models will be used in the design of the new hearing aids and the same patients will be available to help us optimise these aids. The project will have strong clinical involvement. It is supported by an ENT surgeon, and a hearing aid dispenser. They will monitor and advise the project as well as direct suitable patients who wish to volunteer. The Essex hearing research team already includes two audiologists, a speech therapist/audiologist and a computer scientist in addition to the principle investigator (psychologist).

The research will impact on four principal beneficiaries: people with a hearing impairment, clinical professionals meeting the needs of the hearing impaired manufacturers of aids Dr Robert Ferry The hearing impaired Ultimately, the main beneficiaries will be people with a hearing impairment. This is an invisible disability that can severely impair functionality in the workplace and greatly limit the social lives of the billions of people who suffer from it world-wide, particularly the elderly who are most at risk. The main focus of our research is the difficulty they experience in following speech communication in the kind of noisy backgrounds that are characteristic of almost all workplace and social settings. Amplification of quiet sounds has been the traditional focus of hearing aid designs but, paradoxically, this can make the problem of speech-in-noise even worse. A range of remedies exist but none has proved to be universally satisfactory and it is not uncommon for patients to remove their hearing aid when in noisy environments because of the added nuisance! We have good reason to believe that the principles behind the internal regulation of signal level found in normal hearing can be applied to minimise this problem in hearing aids. If we can demonstrate this using a practical, wearable device, the development will be widely welcomed. Dispensers of hearing aids This project and the accompanying Hearing Dummy Project aim to initiate a major change in dispensing practice through the introduction of new patient assessment methods, biologically-inspired hearing aids and the use of computer models of the patient's hearing to tune the aid before dispensing. Dispensers of hearing aids have many patients who experience little benefit from expensive aids and who, consequently, reject the aid. Normally, dispensers have only limited freedom to vary the tuning of an aid using a set of simple rules specified by the manufacturer based on a relatively basic assessment of thresholds and a small set of physical assessments. Patients with similar clinical assessment may have very different outcomes when fitted with an aid using the manufacturer's dispensing guidelines. A guiding principle of the current research is that a more sophisticated assessment of the patient's hearing will provide a better guide to patient outcomes and the basis for more patient-sensitive tuning of the aid. The Hearing Dummy Project has already developed rapid new tests of hearing that will have clinical relevance. Manufacturers The impact for manufacturers will come from the introduction of the new biologically-inspired circuitry described in the case for support. These will improve listening comfort and improve hearing in noisy backgrounds. A major problem for hearing aid manufacturers concerns the dispensing guidelines issued to practitioners for use with their aids. These provide only a rough guide to the best tuning of the aid for a given patient who is asked to 'try' the settings and report back to the dispenser who then adjusts the tuning (often intuitively). Manufacturers currently lack automatic, on-the-bench methods for optimising the tuning of aids. The use of computer models of individualised patient hearing (as proposed in this project) will allow the manufacturer to compare a range of designs and different parameter settings in an objective manner based on the patient psychometric data supplied by the dispenser. Dr Ferry This project offers a unique opportunity for a talented young researcher, Dr. Ferry, to realise the potential of his ground-breaking PhD studies in an applied context. He has developed and published the model of the efferent (negative feedback) regulation of the ear's response to sound that is basic to the new hearing aid design. This could be an excellent start to his career.