New research leads to better infant hearing aids

The University of Western Sydney's MARCS Auditory Laboratories is leading the way with groundbreaking research, exploring the auditory abilities of infants, so hearing aids can correctly amplify the frequencies that babies need to develop communication and language skills.

The study, being run in conjunction with researchers from the National Acoustic Laboratories and the University of New England, is funded through a prestigious Australian Research Council Discovery grant.

Chief Investigator, Dr Christine Kitamura from MARCS, says while newborn screening programs in Australia and overseas are detecting hearing loss just after birth, fitting hearing aids to infants only solves part of the problem.

"At the moment, infants are fitted with hearing aids based on the amplification frequencies that are believed to be best for older children and adults, but there is some uncertainty as to whether these settings are best for infants. So we are now investigating what is best for infants," says Dr Kitamura.

"By amplifying the frequency range that infants best respond to, we can adjust the settings of their hearing aids to improve their exposure to spoken language and the basic aspects of communication."

Dr Kitamura says early detection of hearing deficiencies in infants is vital.

"The first year of life is crucial for children's language development. Not only do they learn the fundamentals of their own language, but the low frequency intonation of mother-child communication forms the basic protocols of social interaction," Dr Kitamura says.

"We know that infants achieve a much higher language level if their hearing loss is identified and treated at a very young age, so by understanding what frequencies we need to enhance in hearing aids, we will improve their future language comprehension and communication skills."

Dr Kitamura says babies aged six and nine months with normal hearing ranges have been tested at the MARCS labs to determine whether they can discriminate between different frequency responses typically found in hearing aids, and which of these they prefer. The next step is to see whether infant wisdom prevails and whether their auditory preferences actually enhance speech intelligibility.

"Because the infants can't tell us whether they can hear differences in speech sounds, we play them the same sound again and again. After a while, the babies become used to the sound, and when a new sound is played they will respond with a longer glance if they can hear the difference between the old and new sounds," she says.

"In order to test which frequency response infants prefer, we give the opportunity of listening to two sounds, or two different frequency responses, and we measure the length of time that babies pay attention to each sound. Babies like this because they are in control and can turn the sounds on just by looking at either of two monitors, one placed to their left and the other to their right. They tend to turn more often to the one they like the most."

Dr Kitamura says the results show just how quickly babies' hearing needs change.

"We found that the six month old babies' responses are stronger to the lower frequencies in speech but by nine months, this response has become more adultlike and infants are more sensitive to high frequency amplification, and their sensitivity to lower frequency sounds has diminished," she says.

Dr Kitamura says further experiments will also be conducted in the coming months on the hearing sensitivities of six year old children and adults for comparison.

"Our preliminary findings on the hearing preferences of infants are certainly encouraging, and provide us with a wealth of new information on how infants process sounds and develop language skills in their first year of life," she says.

"In the future, we hope to use the results from our work to customise hearing aids for babies. And to a child who has never heard their mother's voice, it could make the world of difference."