Contents

1. Introduction
2. Hearing aids
3. Talking with your baby
4. Who does what?
5. Hearing screening for babies
6. What's in a word
7. Sources of information

6. What’s in a word?

Decibels (dB) are used to measure the power of sound. The ear is an amazingly versathe organ. It can detect very, very soft sounds, yet also tolerate sounds which are 1 00 million times IllO~~ powerful before those sounds become uncomfortable. The decibel scale has been designed to help us manage these enormous numbers easily but this means the scale is surprisingly complex and based on logarithms. This means tilat

• 20dB is 10 times more powerful than 10dB
• 30dB is 10 times more powerful than 20dB
• 40dB is 100 times more powerful than 20dB.

In practical terms, the difference between 20dB and 40dB is quite small, from a whisper to quiet speech, but the difference between 60dB and 80dB is large, from normal speech to a shout!

Hearing loss is counted in decibels and the number assigned is, approximately, the level of loudness at which hearing starts. Because sound consists of a range of frequencies (or pitch) the detail of hearing loss is quite complicated. There is further explanation in section 8 of DELTA’s ‘Deaf Children Talking — the Parents’ Guide’.

The frequency of a sound is what gives it it’s different pitch, the difference we hear between a low note played on a piano and a high note. The ‘higher’ the sound, the higher the frequency. Frequency is measured in Hertz (Hz) and kilo Hertz (1kHz = 1000 Hz).

Your child is likely to hear at some frequencies better than others which is why the hearing tests include different frequency sounds. People talk of a ‘high frequency loss’ when the higher frequency sounds (the high notes) are the most difficult for a child to hear. Which type of loss is particularly significant because it affects the understanding of speech. Most vowel sounds (a, e, i, o, u) in English are low frequency but many consonants, like s, t, k, are high frequency so some one with a high frequency loss would not hear the ‘s’ in ‘us’.

Severely deaf means that the average hearing loss across both ears is more than 70dB through to 95dB. This means that hearing aids will he needed to be able to hear people talking. This degree of hearing loss is often present at birth and is usually permanent. Modern hearing aids can provide good quality sound to children with severe hearing losses and with careful fitting, management and consistent use, children call make good progress in talking and learning and develop effective, natural spoken language.

Profoundly deaf means that the average hearing loss across both ears is more than 95dB. This can he as high as i2OdB+. This level of loss is generally present at birth and is permanent. It call be acquired, most commonly through meningitis. Almost all profoundly deaf children have some useful hearing. The best modern aids can produce good quality sound up to 135dB. Few profoundly deaf children need sound to be so loud to enable them to hear — and for those few, cochlear implants now provide an alternative route to sound. Many profoundly deaf children progress well using their hearing to learn to talk.

A hearing aid makes sounds louder i.e. it amplifies them. A child with a severe loss, for example, who has a 75dB threshold (i.e. without her aids she can only hear sounds louder than 75 dB,) might, with the right hearing aids, be able to hear some sounds at 50 dB or less. The level of hearing that is provided by the hearing aids is called ‘the aided threshold’. Hearing aids will not restore full hearing; a deaf child will always be deaf but the effects of hearing loss can be lessened by providing the right hearing aids.

A cochlear implant is a device which helps profoundly deaf children to perceive sound. It does not work like a hearing aid which amplifies sound. It works by using special technology to bypass damaged inner ear structures and send electrical signals directly to the auditory nerve. These are transmitted to the brain and interpreted as sound. One component is placed surgically inside the skin behind the ear and from it an array of electrodes are inserted directly into the cochlea, the innermost part of the ear.

next section: 7. Sources of information