A trend in cochlear implants is the use of faster per-channel pulse carrier rates, promoted on the basis of increased information capacity. However, it is not clear that higher rates achieve this goal in most or ill individuals. Clinical studies present mixed results and research promoting high (e.g., 5000 pps) rales raises important questions. For example, while beneficial, desynchronizing, effects have been reported in many auditory nerve fibers, comparable numbers become adapted to the point of being unresponsive. Furthermore, physiologic dala have only been obtained from intact fibers, not from degenerated neurons typical of chronically deaf ears. Finally, while much is known about neural adaptation to acoustic stimuli, relatively little is known about electrical adaptation, even though the latter typically produces much larger functional changes. We hypothesize that at least part of the variability in performance with higher-rate carriers is due to across-user differences in the auditory nerve's response to high-rate stimuli. This research plan seeks to fill these gaps in our knowledge of how the auditory nerve encodes information presented as modulated pulse trains.
Three Aims are proposed.
Aim 1 will assess signal encoding in fibers excited by modulated carriers at rates relevant to modern and proposed speech processors. Data will be collected from intact and degenerated nerves for greater applicability to clinical cases. Fiber tracing techniques will help link physiology with anatomical status.
Aim 2 will use that data to help develop a computational model of the nerve that accounts for many fiber properties (e.g., integration, refractoriness, and adaptation). This model wsll be used to predict the electrically evoked compound action potential (EC'AP) so that we can tesi: the capacity of ECAP measures to assess fiber functionality, a clinically relevant issue. Finally, Aim 3 will explore the feasibility of applying specific transforms to modulated trains to compensate for adaptation and refractory effects that limit information carried by modulated pulse trains. We expect the results of this work will guide future designs of cochlear-implant speech processors so that modulated stimuli can be better tailored to the encoding capacity of the user's auditory nerve.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC006478-04
Application #
7426363
Study Section
Auditory System Study Section (AUD)
Program Officer
Miller, Roger
Project Start
2005-08-15
Project End
2010-06-30
Budget Start
2008-07-01
Budget End
2009-06-30
Support Year
4
Fiscal Year
2008
Total Cost
$456,460
Indirect Cost
Name
University of Iowa
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
062761671
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Miller, Charles A; Woo, Jihwan; Abbas, Paul J et al. (2011) Neural masking by sub-threshold electric stimuli: animal and computer model results. J Assoc Res Otolaryngol 12:219-32
Hu, Ning; Miller, Charles A; Abbas, Paul J et al. (2010) Changes in auditory nerve responses across the duration of sinusoidally amplitude-modulated electric pulse-train stimuli. J Assoc Res Otolaryngol 11:641-56
Woo, Jihwan; Miller, Charles A; Abbas, Paul J (2010) The dependence of auditory nerve rate adaptation on electric stimulus parameters, electrode position, and fiber diameter: a computer model study. J Assoc Res Otolaryngol 11:283-96
Miller, Charles A; Abbas, Paul J; Robinson, Barbara K et al. (2009) Auditory nerve fiber responses to combined acoustic and electric stimulation. J Assoc Res Otolaryngol 10:425-45
Woo, Jihwan; Miller, Charles A; Abbas, Paul J (2009) Biophysical model of an auditory nerve fiber with a novel adaptation component. IEEE Trans Biomed Eng 56:2177-80
Woo, Jihwan; Miller, Charles A; Abbas, Paul J (2009) Simulation of the electrically stimulated cochlear neuron: modeling adaptation to trains of electric pulses. IEEE Trans Biomed Eng 56:1348-59
Miller, Charles A; Brown, Carolyn J; Abbas, Paul J et al. (2008) The clinical application of potentials evoked from the peripheral auditory system. Hear Res 242:184-97
Miller, Charles A; Hu, Ning; Zhang, Fawen et al. (2008) Changes across time in the temporal responses of auditory nerve fibers stimulated by electric pulse trains. J Assoc Res Otolaryngol 9:122-37
Zhang, Fawen; Miller, Charles A; Robinson, Barbara K et al. (2007) Changes across time in spike rate and spike amplitude of auditory nerve fibers stimulated by electric pulse trains. J Assoc Res Otolaryngol 8:356-72