Malcolm Gladwell reports that it takes 10,000 hours of practice to learn something new. Hart and Risley report that typical children hear about 46 million words by age 4. Dehaene reports that a child needs 20,000 hours of listening as a basis for reading. Pittman reports that children with hearing loss require three times the exposure of typical hearing children to learn new words and concepts because of the reduced auditory bandwidth caused by hearing loss.
What does this mean for our children with hearing loss? It means that we need to be sure they have as good auditory access as possible. They need to hear everything they can possibly hear if they are going to use audition to learn. So everyone working with children with hearing loss needs to be sure they have technology that is performing maximally. Good enough is not good enough here.
What does it take for a child with hearing loss to succeed?
For children with hearing loss to succeed they need language at age level, literacy skills at age level and social skills at age level. What does it take to obtain these goals? Early identification, aggressive audiological management with technology fit at the String Bean (top of the speech banana), full time use of technology every waking hour, listening in acoustically favorable environments, auditory based therapy, family support, a rich language environment (talk, talk, talk, using complex language models), and educational programs willing and able to make the necessary adaptions for maximizing learning.
It is a long list but a critical one. Everyone who works with children with hearing loss is responsible for making sure that children have all they need. It is not enough for the audiologist to fit the technology and then move on to other things, or for the listening and spoken language specialist to provide therapy and educate the family. We are all responsible for covering all the bases and making sure that children have everything they need. Audiologists need to ask what is happening in therapy, how the child is hearing in school, how noisy the home is, and therapists need to monitor performance with technology, and ask about school and home.
Only by having all of us responsible for everything, and by listening to each other, will children be the best they can be.
What does intelligible speech look like?
Hearing something is not the same as hearing well. A child may hear with technology, may know that someone is speaking to him, but not hear all the phonemes of speech. Not acceptable. Access to intelligible speech requires that children hear every phoneme, not just the Ling 6.
The Ling 6 is a screening test and good for a quick check. The equivalent diagnostic test is one in which children are tested to see if they can perceive every phoneme. Time consuming, yes. Valuable? Absolutely. Using something like the Medial Consonant Test, in which we ask kids to repeat /aba/, /afa/, /ata/, etc. allows us to understand exactly what a child can hear well and what sounds are being confused. It is very useful in determining how to change technology settings to provide access to frequency bands that the child is missing.
Children need to hear though the high frequencies if they are going to hear sibilants and fricatives. That means they need to hear through 6000 and 8000 Hz. Children need to hear normal and soft conversation, and they need to hear in competing noise. They need to hear well at soft levels (30-35 dB HL) if they are going to overhear conversation around them and hear peers in school and on the playground. They need to hear both for language exposure and for social skills. Children who cannot hear their peers calling out directions during games will soon not be welcome to play.
We can only know what a child hears by testing. That means testing in all conditions in which it is important that a child hears. We cannot assume that a child is hearing at a sufficiently soft level or has normal speech perception without testing. Speech may be audible but not intelligible.
Vowels carry 90% of the audibility but only 10% of intelligibility. Consonants carry 10% of the audibility but 90% of intelligibility. It is often difficult to help parents understand that the fact that a child knows you are talking does not mean that speech is intelligible. But, we need to figure out a way to help everyone working with the child understand.
What is good speech perception?
It is important that we accurately describe speech perception test results. We are not doing speech perception testing just as a casual activity. Test results are critical to planning management. How should we describe test results. Children with hearing loss who are in mainstream educational settings need to be assessed using the same protocols we would use for their typical hearing peers because they need to hear in the classroom as well as their peers. See table 1.
Table 1: Speech Perception Qualifiers (Madell et al 2011)
If a child has a speech perception score of 74% and we describe it as good or excellent, the message we are giving is that this child is doing well and nothing has to change in his management. But if we say that speech perception is fair, audiologists will feel the need to try and improving hearing with the technology, therapists will work on improving speech perception skills and teachers will have realistic expectations for hearing in the classroom. We do no one a favor if we describe hearing as better than it is.
How do we know that auditory access is sufficient?
For children to have sufficient auditory access, they need to hear in the string bean – at the top of the banana. That means thresholds at 20-25 dB through out the frequency range. Let’s remember that soft speech is at about 30-35 dBHL.
Children need to be hearing soft speech if they are going to overhear conversation – critical for language and social skills. If technology thresholds are at 30 dBHL, the child will not hear soft speech. Think about what that means for language. Audibility is not a guarantee of intelligibility but lack of audibility guarantees lack of intelligibility.