AUDITORY BRAINSTEM IMPLANTS

Neurofibromatosis Type II (NF-2) is a disease in which patients develop multiple tumors of the central nervous system, including bilateral acoustic neuromas (vestibular schwannomas). Profound deafness is the usual outcome following removal of the acoustic neuromas in these individuals. Researchers have developed auditory brainstem implants that can deliver stimulation to the cochlear nucleus, bypassing the damaged nerve, in patients undergoing such surgery (House and Hitselberger, 2001).

The present auditory brainstem implant (ABI) is approved by the FDA for use in patients with NF-2. The device has a Silastic pad with 22 electrode contacts that are placed adjacent to the dorsal cochlear nucleus in the brainstem following tumor removal. Some patients who receive an ABI do not receive any auditory benefit from the device, and the patients must fully understand this, as well as the risks and potential side effects of surgery, prior to implantation. The most recent results with the ABI can be found in an article by Otto et al. reporting on the 55 subjects that were included in the FDA clinical trial with this device (Otto, Brackmann, Hitselberger, Shannon, and Kuchta, 2002).

OTHER ASSISTIVE LISTENING DEVICES

In addition to conventional hearing aids and cochlear implants, there is a category of technologies called ALDs. These devices are typically used part-time either instead of, or in addition to, hearing aids or implants. They are usually targeted toward improving communication functionality in specific limited situations, such as talking on the telephone, communicating over a distance, attending the theater, or detecting a doorbell ring. A recent review of ALD types and technologies is found in Compton (2000).

Varieties of ALDs may be partitioned into two categories: acoustic and alerting. Acoustic ALDs facilitate the reception of acoustic signals by reducing the corruption of desired sounds that occurs in many everyday listening situations, for example, background noise (including speech babble), reverberation effects in auditoria, large distance between talker and listener, and limited visual cues resulting from poor lighting or a talker who cannot be seen.

Amplified telephones are probably the most widely used and effective acoustic ALDs (Kochkin, 2002). Another effective type of device employs a wireless system composed of a transmitter and receiver pair. The transmitter is driven by a microphone that is held by or near the talker. The signal is broadcast to the receiver using FM radio, induction loop, or



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