The current status of cochlear implants

Abstract

In the University of Sydney cochlear implant programmes, 109 adults and teenagers have received a 22 electrode cochlear implant (Cochlear™ implant) since 1984; and 127 children have received a Cochlear™ implant since 1987. The results were analysed when all patients were still using the MSP speech processors rather than the newer SPEAK processors. Seventy five percent of adults and teenagers deafened after learning speech for a period of less than 15 years were able to recognise some words by audition alone. Only 30 percent of adults and teenagers deafened for over 15 years regaining hearing were able to recognise any words by audition alone but most found the device very helpful in aiding lipreading. None of adults and teenagers who were born deaf who received a cochlear implant found they could recognise any sounds and half of them abandoned using the device.

Children who were deafened after learning speech usually did extremely well with a cochlear implant and could remain in their regular school situation. Children who had done well with hearing aids were also very likely to succeed with a cochlear implant. Children who had learnt to communicate by gestures or signs who had reached an age of over 6 years did poorly with the cochlear implant with 73 percent unable to recognise speech by listening alone and unable to improve their speech production to an intelligible level.

Children born deaf who received the implant early in life and were taught primarily through audition could be very successful with 52% recognising words by audition alone and gaining intelligible speech. Preliminary studies suggested that the younger the child received the cochlear implant the greater the possibility of success.

Neural plasticity or the ability to the brain to learn or relearn tasks appear to be the most important factor affecting the selection of candidates for a cochlear implant. It appeared that after the age of 6 years, if a child had not utilised the auditory and motor areas of spech production within the brain, the neural plasticity remaining was insufficient to allow effective use of a cochlear implant.

The cochlear implant is a device which can restore when a person is too deaf to be able to use a conventional hearing aid. The cochlear implant does not provide normal hearing but may provide sufficient information for the recipient to distinguish several words without the need for lipreading. Evidence will be presented which shows that the device can enable children suffering from congenital deafness to gain excellent speech and listening providing it is fitted at an early age and there is an appropriate training programme to teach the child.