Role of audiologist
The audiologists with the Cochlear Implant Program at The Hospital for Sick Children play an essential role in establishing a child's candidacy for cochlear implantation as well as overseeing the child's audiological care following cochlear implantation. The audiologist typically serves as the child's case manager during the pre assessment period guiding the family through the period of assessment. When the child receives his cochlear implant, the audiologist will then manage his case until the child has reached the age of 18. The audiologist can provide the family with an abundance of information on cochlear implants in children. The audiologist can also provide the family with support throughout this process.
In order to determine if a child is audiologically a candidate for a cochlear implant, a battery of tests are administered. These tests typically include:
- pure tone air and bone conduction testing
- electroacoustic analysis of hearing aids
- aided soundfield testing
- otoacoustic emissions
- evoked auditory brainstem response
- a number of speech perception tests
Remember: Audiology is only one part of the assessment process. A multidisciplinary team determines a child's candidacy for a cochlear implant.
After the Surgery
Following the surgery, the child's cochlear implant is not immediately activated. The external equipment is provided three weeks after the surgery, and the implant is activated one week after that.
Approximately three weeks after the surgery, the family returns to the hospital and is given the external components of the cochlear implant.
The audiologist explains how to operate the device. This allows both the family and the child to become familiar with the manipulation of the equipment and for the child to become accustomed to wearing the equipment for a week before the implant is activated.
Older children may not need this step and may instead have a combined appointment to receive the external equipment and activate the implant on the same day.
Approximately four weeks after the surgery and one week after receiving the equipment, the child returns to the hospital for the activation of the implant. The audiologist uses a computer, customized software and a special interface to set appropriate levels of electrical stimulation for each electrode. With the child's equipment attached to the audiologist's computer, T (threshold) and C (comfort) levels are determined. T level is defined as the lowest Current Level to elicit a very soft, but consistent hearing sensation. The C level is defined as the maximum Current Level that does not produce an uncomfortable loudness sensation for the individual. This information is stored in the memory of the speech processor and is called a program or MAP (Nucleus Technical Reference Manual, 1999).
When the speech processor is turned on, the child can hear sound. With older children, who are able to report on sound quality, the audiologist can make adjustments to the MAP to optimize sound quality.
Because T and C levels may change over time regular MAPping occurs 5-6 times within the initial year of activation. Children are then typically followed every six months for routine MAPping.