Cochlear Implant Research Laboratory

Cochlear Implants: Restoring Hearing to the Deaf

Donald K. Eddington, Ph.D.
Victor Noel, Meng Yu Zhu, Margaret Lankow
Cochlear Implant Research Laboratory
Tel: 617-573-3767

Most people who suffer profound hearing impairment have lost the ability to translate the acoustic energy of sound into the electrical signals carried to the brain by the auditory nerve. Cochlear implants are electronic devices that are designed to bypass the external and middle ears and produce sound sensations by exciting the auditory nerve directly. These devices are in two parts: an external sound processor and an implanted receiver/stimulator with electrode array. The external sound processor is housed in a behind-the-ear hearing aid case that includes a microphone and electronics that translate acoustic signals into instructions that are transmitted across the skin to control the receiver/stimulator implanted behind the ear. The stimulator generates electric stimuli that are delivered to auditory nerve fibers using an array of electrodes implanted in the deaf patient's cochlea (inner ear). These stimuli produce nerve activity that the brain interprets as sound.

The goal of these devices is to elicit patterns of nerve activity that mimic those of a normal ear for a wide range of sounds. Such a system would not only enable postlingually deafened individuals with a suitable number of remaining nerve fibers to spontaneously recognize all types of sound (including speech), but would also provide the input required for many children deafened at a young age to acquire speech communication. While this goal has not yet been completely realized, the hearing provided by today's devices enables a few to communicate without lip-reading and most to communicate fluently when the sound is combined with lip reading.

Work in the Cochlear Implant Research Laboratory focuses on the fundamental mechanisms underlying the sound sensations produced by electric stimulation of the auditory system. For example, results from computer models of electric current flow in the implanted cochlea and from models of how these flows excite nerve fibers are combined with the results from a wide variety of tests (e.g., threshold, discrimination and speech recognition) conducted in implanted human subjects to provide a rational basis for the design of new and refined sound processing schemes.

Based on these fundamental studies, we are developing and testing new sound processing schemes that, in the laboratory, provide significant improvements in speech reception for some subjects. These new sound processing techniques will be field-tested using a programmable, wearable sound processor.

Representative Publications

Litvak, L, Delgutte B and Eddington DK, “Improved neural representation of vowels in electric stimulation using desynchronizing pulse trains,” Journal of the Acoustical Society of America 2003; 114: 2099-2111.

Somdas MA, Li PMMC, Whiten DM, Eddington DK, Nadol JB, “Quantitative evaluation of new bone and fibrous tissue in the cochlea following cochlear implantation in the human,” Audiology & Neurotology, 2007; 12:2770284.

Eddington DK. Speech recognition in deaf subjects with multichannel, intracochlear electrodes. Ann N Y Acad Sci 1983; 405:241-258.

Wilson BS, Finley CC, Lawson DT, Wolford RD, Eddington DK, Rabinowitz WM. Better speech recognition with cochlear implants. Nature 1991; 352:236-238.

Rubinstein, JT. Axon termination conditions for electrical stimulation. IEEE Trans Biomed Eng 1993; 40:654-663.

Eddington DK, Girzon G. An electroanatomical model of intracochlear electrical stimulation, I: formulation, solution and predictions. Hear Res 1994 (submitted).

Eddington DK, Girzon G, Cuneo PA. An electroanatomical model of intracochlear electrical stimulation, II: tests of model predictions. Hear Res 1994 (submitted).

page updated: 2/29/08