Towards a better speech processor for cochlear implants : auditory- nerve responses to high-rate electric pulse trains

Cochlear implants are prosthetic devices that seek to restore hearing in profoundly deaf patients by electrically stimulating the auditory-nerve (AN). With current implants, the representation of the sound waveform in temporal discharge patterns of the auditory nerve is severely distorted. The distortion is particularly significant at higher (>600 Hz) frequencies, for which the period of the electric stimulus is near the AN refractory period. For example, in response to a 1000-Hz pulse train, most AN fibers may fire on every other stimulus cycle, so that the AN population would represent half of the stimulus frequency rather than the actual frequency. Rubinstein et al. [Hearing. Res. 127, 108] proposed that the coding of electric waveforms in cochlear implants can be improved if a sustained, electric high-rate (5 kpps) desynchronizing pulse train (DPT) is presented in addition to the information-carrying electric stimulus. The DPT may amplify the inherent noise in ANfibers so as to produce ongoing, stochastic discharges similar to the spontaneous activity in a healthy hear. We tested this hypothesis by recording responses of ANfibers of deafened cats to sustained electric pulse trains. For most fibers, responses to the DPT showed adaptation during the first 2 minutes, followed by a sustained response for the remainder of the 10-minute stimulus. These sustained responses partially resembled spontaneous activity in terms of discharge rate and interspike interval distributions. AN fibers were extremely sensitive to modulations of the DPT, responding tomodulations as small as 0.5%.

Department dc:contributor.department

Harvard University--MIT Division of Health Sciences and Technology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Litvak, Leonid, 1973-

Advisor dc:contributor.advisor

• Bertrand Delgutte and Donald K. Eddington.

• Harvard University--MIT Division of Health Sciences and Technology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/16817

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16817