Tackling 'dead' hearing regions

Deafness Research UK's adviser on hearing aids, Professor Brian Moore, is leading a three year project that aims to improve the fitting of hearing aids by developing more accurate ways of measuring hearing loss at different frequencies.

It should result in more effective hearing aids and a better quality of life for the hard of hearing.

Gradual deterioration of hearing means that, for most people, hearing impairment is an unwelcome feature of later life. Half of all people over the age of 60 are affected - making it the most common disability among older people.

Hearing loss makes it difficult to participate in conversations. It can cause embarrassment and frustration and many affected people withdraw from social situations, leaving them feeling lonely and socially isolated.

Because hearing does not generally deteriorate evenly across all frequencies - older people often have reduced ability to hear higher frequency sounds while retaining the ability to hear lower frequency sounds, for example - a hearing aid should provide more amplification in the frequencies where they are needed.

However, in some people, damage to the sensory hair cells of the inner ear is so extensive that sounds at affected frequencies either cannot be heard even when highly amplified or are heard with distorted pitch and tone quality. People affected in this way are said to have "dead" hearing regions; the main difficulty they experience is in understanding speech, because it encompasses both high and low frequencies.

Currently, precise diagnosis of dead regions is difficult and, however carefully they may be fitted, many people find that hearing aids are of limited help.

This project aims to devise a set of signals which it is hoped can be incorporated into standard testing procedures to enable accurate diagnosis of patterns of hearing loss and identification of dead regions.

An estimated 270,000 people in the UK alone stand to benefit from this research, which is being carried out at the Department of Experimental Psychology, University of Cambridge.

"This research will give us access to more accurate information about individual patterns of hearing loss at different frequencies, and about the extent of dead regions, in turn enabling better fitting of hearing aids," says Professor Moore. "For example, if two people have the same audiogram, but one has dead regions, that person's aids will need to be programmed differently.

"At the same time, we are developing novel amplification strategies for hearing aids which we hope will help people with dead regions of hearing. We are looking at various methods of providing extra information about speech for people with dead regions. One way of doing this is by 'transposition', where some of the higher frequencies in speech are converted to lower frequencies, which can be better heard and analysed.

"We hope that the combination of more accurate testing with new generation hearing aids should improve speech comprehension for people with dead regions of hearing. This research will also help in the assessment of need for cochlear implants."