KidsAudiologist

What can my child hear?

Posted on: March 13, 2012

More than 9 out of every 10 chldren born with a hearing loss have hearing parents. It’s therefore entirely natural that early on they are going to ask “What can my child actually hear, what does it sound like for them?” They share a need to try and get to grips with this as part of the process of understanding what they need to do to help their child. It is a very difficult question to answer. Some of the things we know at this stage include the degree and type of deafness: we know how much volume is lacking for a mild (20-40dB), moderate (41-70dB), severe (71-95dB) or profound (95+dB) hearing loss, and we know that loss of hair cells in sensorineural hearing loss means that some natural processing that happens within the cochlea is lost – including the cochlea amplifier, pitch discrimination and the ability to recognise different sound levels (reduced dynamic range). We also know a good amount about the benefits and limitations of various types of hearing technologies that are used. Now more than any time in history, we know that almost all deaf children can perceive the full range of speech sounds with their hearing aids or cochlear implants. But we also know that they can’t do this as easily as hearing children and that no hearing technology can replace normal levels or quality of hearing.

So it’s relatively easy to mock up some simulations of what a hearing loss might sound like using some software to reduce the overall level of sound and filter out some of the frequencies that make up speech sounds. There are some good ones available online and my favourite is the Better Hearing Institute which has mild and moderate hearing loss in different situations. The NDCS also have a couple of examples that are specific to children in classrooms.

But there is a health warning about these simulations and that is that we don’t know, especially in the early days following diagnosis in young babies, what is happening beyond the ear and how well they can make sense of the sound they hear. Hearing, listening and understanding are sophisticated processes that are determined by a complex interaction between the physical properties of the ear as well as attention, memory and auditory processing (what happens when your brain recognises and interprets sound so that it becomes meaningful). The brain has the incredible power of plasticity in the early years and is continually moulding and learning from new experiences and sounds. As adults the brain is much less plastic and it takes much longer to adapt. This means that the experience of hearing and listening is hugely variable between individuals and is influenced by whether someone is born deaf or what age they became deaf, how long it was between developing a hearing loss and being fitted with hearing aids, their listening experience, and their cognitive and auditory processing abilities. Children born deaf and those who become deaf early in life experience deafness as the norm. Older children, teenagers and adults who become deaf have a very different experience of deafness to which they need to psychologically and physically adapt to. Much of what we understand hearing loss to sound like comes from adults who have previously experienced normal hearing levels. This is a particular issue when parents are considering a cochlear implant for their child for example. It is commonly reported that cochlear implants sound electronic, that they aren’t natural, and that voices sound like ‘a Dalek underwater’. This can be a devastating idea for parents considering this option but in fact when you speak to these same implanted adults later on they describe their implants as sounding very natural as their brain has acclimatised to the new sound. I recently chatted with a group of teenagers who all used cochlear implants and they agreed – “people think they sound like robots, but they don’t”. Just from listening to the voice quality of the thousands of implanted children, we can be certain that they do not experience this kind of ‘electronic’ sound. But to listen to this type of electronic simulation the best one I’ve found is Scientific American Frontiers.

Auditory Neuropathy Spectrum Disorder (ANSD) affects approximately one in 10 deaf children and causes distortion of sound and difficulty discriminating speech over and above what we would expect from the hearing loss alone. The level of distortion is highly variable from very slight to very severe and it is not measurable. So in young children we do not know early on how it will affect their speech and language development. Simulations of ANSD from mild to profound neuropathies can be heard here and make scary listening but again we know that with the right intervention children with ANSD are successfully using their hearing and using spoken language.

There are 10 million people in the UK have some degree of hearing loss and the majority of these people experience age-related deterioration of hearing. At the other end of the age spectrum there are just 45,000 under 18’s with a permanent hearing loss. Inbetween there are those adults who grew up with a hearing loss as well as those who have lost their hearing as an adult. My experience is that individuals (and their parents or family) use a wide variety of terms to describe their hearing level – deaf, hearing loss, partially hearing, hearing impaired, hard of hearing – and they rarely relate to their audiogram level. There are those people who associate themselves culturally with the Deaf community who we may traditionally think of as those who are profoundly deaf sign-language users. But there are also people who have developed a mild hearing loss for the first time who may tell their audiologist they are ‘stone deaf’ or ‘can’t hear a thing’ and this is their perception compared with their normal experience.

Every child’s hearing levels and hearing experience is unique and it is impossible for these types of simulations to represent how all deaf people process and experience sounds heard. But they are useful in giving the listener an understanding of the difficulties encountered and I particularly like those that can highlight the big differences experienced between listening in quiet and noisy environments and which are an important reminder of how much easier we can make life for children by improving their listening environments in school and elsewhere.

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