There is a great variability in the speech recognition performance of cochlear implant patients. For a given type of implant, auditory performance may vary from zero to nearly 100% correct. Auditory performance is defined here as the ability to discriminate, detect, identify or recognize speech. A typical measure of auditory performance is the percent correct score on open-set speech recognition tests. The factors responsible for such variability in auditory performance have been the focus of research for many years. Some of the factors that have been found to affect auditory performance are listed below:
• Duration of deafness
The duration of deafness prior to implantation has been found to have a strong negative effect on auditory performance. Individuals with shorter duration of auditory deprivation tend to achieve better auditory performance than individuals with longer duration of auditory deprivation.
• Age of onset of deafness
The age of onset of deafness has a major impact on the success of cochlear implants depending on whether the deafness was acquired before (prelingual) or after (postlingual) learning speech and language. It is now well established that children or adults with postlingual deafness perform better than children or adults with prelingual or congenital deafness.
• Age at implantation
Prelingually deafened persons who were implanted in adolescence have been found to obtain different levels of auditory performance than those implanted in adulthood. People implanted at an early age seem to perform better than people implanted in adulthood. It still remains unclear, however, whether children should be implanted at a minimum age of 2 years for maximum auditory performance.
• Duration of cochlear implant use
Duration of experience with the implant has been found to have a strong positive effect on auditory performance for both adults and children. The speech perception and speech production skills of children continue to improve over a four year period following implantation.
• Other factors
Other factors that may affect auditory performance include: (1) number of surviving spiral ganglion cells, (2) electrode placement and insertion depth, (3) electrical dynamic range, and (4) signal processing strategy. There are also factors, such as patient’s level of intelligence and communicativeness, which are unrelated to deafness but may also affect auditory performance. Aural rehabilitation, commitment from the cochlear implant patient in terms of time and effort, and support from family, friends and workplace also play an important role.