THE LABYRINTH AND THE EIGHTH NERVE
the same unit as the microphone and the amplifier and the sound is piped
into the ear by a narrow plastic tube.
In patients with conductive deafness, simple amplification will give
excellent results. In sensorineural deafness there are problems of distortion
and recruitment and in many cases the results are disappointing. To a large
extent the aid can be selected so that it is powerful enough to compensate
for the rise in the threshold of hearing. The frequency response can be
adjusted to compensate for the different losses at different frequencies but
the matching is never accurate and often a trial of several similar instruments
is required to get the best results. When a hearing aid is first fitted there is
often difficulty in picking out the sound that the patient wishes to hear from
the background noise which is also amplified. With practice and perseverance
this problem tends to diminish as does the intolerance of loud sounds
particularly where there is recruitment.
2. Non-electrical Hearing Aids. The simplest form of non-electrical hearing
aid is cupping the hand behind the ear and this method is often brought into
use subconsciously by the deaf. Various forms of ear trumpet can still give
useful service, particularly in the elderly or the disabled who have difficulty
in manipulating the small electrical aids.
3. Lip Reading. All patients with incurable progressive deafness should be
advised to learn to lip read as early as possible. Its acquisition becomes more
difficult with increasing deafness and age. Some people learn to lip read
spontaneously but instruction by a trained teacher is recommended. Lip
reading is not only useful to .the severely deaf but in the partially deaf it gives
additional information particularly helping in the
sonanis which tend to be cut off by deafness affecting the higher frequencies.
4. Speech Therapy. In severe- sensorineural -deafiaess the patient has
difficulty in hearing his own voice so that he is unable to monitor its quality
and loudness. Eventually, speech becomes slurred, flat in tone and raucous.
This loss of quality of speech can be delayed by speech therapy.