1993 WINNER

Emily Beardall
St Aidan's High School, Harrogate
Winner of the 16-19 category

28 Jun 1993

Science: How to hear with a bionic ear
Emily Beardall describes a programme that is helping profoundly deaf children

By EMILY BEARDALL

WHEN children suddenly lose their hearing, the effects upon their social, emotional and educational development can be devastating. An electronic device known as a cochlear implant is giving some profoundly deaf children the chance to hear again.
The human ear is a vulnerable organ. It is divided into three parts (see diagram): the outer ear, the middle ear, which is made up of the ear drum and a chain of tiny bones called ossicles, and the inner ear.

This is also known as the cochlea, in which hair cells are stimulated, generating an electrical current in the auditory nerve which then transmits the signals to the hearing centres of the brain.

The important hair cells of the cochlea can be damaged by trauma or meningitis. Even the most powerful hearing aids are ineffective if the function of both inner ears is impaired.

The cochlear implant has been developed at the University of Melbourne by Prof Graham Clark and his colleagues. It is designed to stimulate the user's auditory nerve directly, bypassing the damaged inner ear.

Whereas the conventional hearing aid uses sound vibrations, the cochlear implant converts sound vibrations into electrical stimuli which are picked up by the auditory nerve and transmitted to the brain.

Sounds are collected by a microphone and are then converted into electrical signals by a speech processor. This processor passes on the signals to 22 electrodes surgically implanted inside the cochlea, which send the impulses to the brain via the auditory nerve. The microphone and transmitter are fitted behind the ear, the transmitter being held in place by a magnet in the receiver which is buried under the skin.

At first, only children who had been deafened during childhood received cochlear implantation because they already had some experience of normal hearing. Even then, the implant has been used only where a conventional hearing aid would not be effective. More recent developments have allowed congenitally deaf children to have the operation.

Implantation is seen as beneficial only to those with no other learning and health problems; parents and teachers must also be willing to support the children by following a rehabilitation programme.

If a child fits these criteria, an audiological and medical examination must be conducted, followed by counselling. The school is also visited to find out whether its facilities would support the rehabilitation programme. The decision to implant is then made by a surgeon.

After the operation, the child is seen by a teacher of the deaf in preparation for switching on the 'bionic ear'. The child is shown how to use the equipment and is taught about everyday situations involving loud noises.

'Switch-on' refers to the fitting of the external parts of the device. Over three days each electrode is tuned by measuring the threshold level and maximum comfort level which defines the usable range.

If the initial communication skills of the child are poor this can take some months of hospital visits. The child is also taken for listening walks to become aware of outdoor sounds.
Play is also encouraged with sound-making toys to develop confidence and pleasure in using the device before moving on to more complicated tasks, such as listening to language. When tuning is complete, progress is monitored frequently and a speech therapist works on communication skills.

So far, 60 children in Britain have received implants, the cost of the programme being about pounds 30,000 per child. This includes the staffing needed to carry out assessments, surgery, tuning and rehabilitation.

Implantation is also available to selected adults, although the expense and the long rehabilitation period have restricted research to those people for whom the optimum results could be obtained.
Perhaps in future the miracle of the 'bionic ear' will enable sound to be a sense which we can all enjoy.

Copyright: Telegraph Group Ltd