How well does a child with hearing loss have to hear?
Well, that depends on how well we want him to learn using audition. With today’s technology, children with hearing loss have the opportunity to use auditory for language learning and for academics. But we should never assume that because the child is wearing hearing aids he is hearing optimally. For a child to use hearing to learn they need to be able to hear both normal and soft conversation in quiet, and in competing noise. That is a tall order. How do we know if we have accomplished our goal?
The Speech Banana
Everyone working with children with hearing loss knows about the speech banana. The speech banana was designed to help us understand where different phonemes are found – at what frequencies and at what intensities. This speech banana is found at the Listening and Spoken Language Knowledge Center of A. G. Bell Association Speech Banana).For example, by looking at the speech banana we see that the phoneme /d/ has energy at around 350 Hz and /f/ has energy at around 4000 Hz. If we were to draw a child’s aided thresholds onto the speech banana with the phonemes on it, we would be able to estimate what a child will be able to hear, and which phonemes she will be missing. In another way, by listening to a child’s speech production, we should be able to draw the audiogram. (In fact, when I was first working at the League for the Hard of Hearing in NY in 1970, the director, Dorothy Noto Lewis, asked all the audiologists to do exactly that. By talking with the child, before we tested, we had to draw out what we thought hearing would be with and without hearing aids. This skill has stood me in very good stead over the years. I just used it last week when I did a home visit with a baby. I tested the baby by repeating phonemes and knew exactly what to tell the audiologist to change in the hearing aid settings.)
Is Hearing Anywhere in the Speech Banana Sufficient?
If you look carefully at the speech banana you will find that the phonemes are located both at different frequencies and at different intensities. So if a child has aided thresholds at about 35-40 dB HL they will definitely be hearing within the speech banana but they will be missing many of the phonemes. So, are they hearing enough? Obviously not.
The Speech String Bean
Our goal is to have children hear EVERY phoneme, not just the Ling Sounds (ah, ee, oo, m, sh, s) but every sound in whatever language they are learning. The way we do that, is by being certain that their technology is fit so that they are hearing at the top of the speech banana. Let’s call it the speech string bean. That green line at the top of the banana is my goal. You can call it a string bean, or an asparagus if you prefer, but the goal is to be sure that kids are hearing right there at the top. Only by being sure that kids are hearing at the level of the string bean can we be sure they are hearing every phoneme.
How Do We Know if the Child is Hearing at the Level of the String Bean?
We can only know if a child is hearing at the level of the string bean if we test. Real Ear measures do not tell us what a child hears. They are only an estimate. They tell us what sound is reaching the eardrum but nothing further up the auditory pathway, and nothing about what is reaching the auditory brain. We need to obtain aided thresholds for each ear separately for every child to know that they are hearing at a sufficiently soft level. If they are not, it is the responsibility of the audiologist to try and modify the hearing aid settings, try new hearing aids, or consider a cochlear implant if a child is not hearing well enough with his current technology.
Are Aided Thresholds Enough?
No, aided thresholds are not enough. As important as they are, we need to test speech perception also. A more detailed discussion about testing speech perception is found in Speech Perception – The Basics but in summary, we need to test speech perception at normal and soft conversational levels in quiet and in noise, and we need to test each ear separately as well as both ears together. In addition to standard audiological testing, listening and spoken language therapists, teachers of the deaf, speech-language pathologists and classroom teachers need to pay attention to what children hear and what they are missing. That information needs to be shared with the child’s audiologist who can use that information to improve performance.
The concept of the Speech String Bean is really critical in helping us understand what our goal is for children to hear. It is something that families as well as all clinicians working with children with hearing loss need to understand.