The number of people who are deaf and who receive bilateral cochlear implants (CIs) has grown substantially in recent years. Many bilateral CI users demonstrate significant benefits from bilateral implantation, such as better speech-understanding in noise and improved sound localization. However, the performance of many patients is still notably worse than that of normal hearing (NH) listeners. Proposed experiments will systematically investigate a number of factors that are likely to contribute to the gap in performance. We will use a multi-pronged approach to integrate a number of research methodologies that are concerned with spatial and binaural hearing. Methods will vary from having tight control over the signals presented to the auditory nerve to difficult-to-control stimuli presented in free field. Within this range, using novel binaural research processing strategies, we will manipulate the stimulus naturalness, from unrealistic non-speech stimuli, such as electrically pulsed signals presented to single pairs of electrodes, to the most realistic of stimuli, speech presented under complex multi-source listening conditions. By combining control with naturalness we aim to better understand what conditions are likely to maximize the success of cochlear implant users. In addition to offering opportunities for translation from research to clinic, the proposed research asks questions that probe auditory mechanisms in normal-hearing listeners and aims to provide knowledge that can advance basic science. These studies are conducted using models that simulate cochlear implant listening.
Aim 1 investigates factors at the level of individual electrically pulsed signals. Using a research processor designed to carefully control selected binaural pairs of electrodes, cues that are known to be important for binaural hearing will be introduced to multiple electrode pairs, simulating aspects of real-world listening and testing effects of electrode mismatch across the ears.
Aim 2 uses digital signal processing for audio signals. Using a custom made binaural program, clinical speech coding strategies with varying numbers of pitch-matched binaural channels are used. We will aim to demonstrate conditions under which preservation of binaural cues offers advantages for binaural abilities in bilateral CI users that have not been previously seen.
Aim 3 is to investigate the effects of age of deafness and age at onset of bilateral hearing on performance. We will systematically recruit patients into prospective groups that vary according to pre-lingual, mid-childhood or adult onset of deafness, with unilateral and bilateral activation ages controlled. We will test hypotheses about auditory plasticity and its impact on binaural hearing. Overall, this project will offer opportunities for translation from research to clinic with important clinical implications in terms of bilateral fitting choices, rehabilitation and counseling. In addition, we will advance basic science in the auditory field by investigating mechanisms in NH listeners under degraded listening conditions.

Public Health Relevance

This research is aimed at advancing knowledge in auditory science, focusing on binaural hearing in deaf people who use bilateral cochlear implants.
We aim to better understand what conditions are likely to maximize the success of cochlear implant users. Findings will have a direct translational component, with regard to bilateral fitting choices, rehabilitation and counseling. Findings will have relevance to children who are deaf, because parents often struggle with the decision regarding bilateral implantation vs. "saving an ear" for future technology. If bilateral CIs cannot ultimately provide excellent binaural hearing, and if alternative treatments for deafness become feasible, our work will be of importance to pediatric decision making.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IFCN-B (04))
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Donahue, Amy
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University of Wisconsin Madison
Schools of Arts and Sciences
United States
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Kan, Alan; Litovsky, Ruth Y (2015) Binaural hearing with electrical stimulation. Hear Res 322:127-37
Jones, Heath; Kan, Alan; Litovsky, Ruth Y (2014) Comparing sound localization deficits in bilateral cochlear-implant users and vocoder simulations with normal-hearing listeners. Trends Hear 18:
Gartrell, Brian C; Jones, Heath G; Kan, Alan et al. (2014) Investigating long-term effects of cochlear implantation in single-sided deafness: a best practice model for longitudinal assessment of spatial hearing abilities and tinnitus handicap. Otol Neurotol 35:1525-32
Churchill, Tyler H; Kan, Alan; Goupell, Matthew J et al. (2014) Speech perception in noise with a harmonic complex excited vocoder. J Assoc Res Otolaryngol 15:265-78
Tolnai, Sandra; Litovsky, Ruth Y; King, Andrew J (2014) The precedence effect and its buildup and breakdown in ferrets and humans. J Acoust Soc Am 135:1406-18
Churchill, Tyler H; Kan, Alan; Goupell, Matthew J et al. (2014) Spatial hearing benefits demonstrated with presentation of acoustic temporal fine structure cues in bilateral cochlear implant listeners. J Acoust Soc Am 136:1246
Ihlefeld, Antje; Kan, Alan; Litovsky, Ruth Y (2014) Across-frequency combination of interaural time difference in bilateral cochlear implant listeners. Front Syst Neurosci 8:22
Goupell, Matthew J; Litovsky, Ruth Y (2014) The effect of interaural fluctuation rate on correlation change discrimination. J Assoc Res Otolaryngol 15:115-29
Goupell, Matthew J; Stoelb, Corey; Kan, Alan et al. (2013) Effect of mismatched place-of-stimulation on the salience of binaural cues in conditions that simulate bilateral cochlear-implant listening. J Acoust Soc Am 133:2272-87
Goupell, Matthew J; Kan, Alan; Litovsky, Ruth Y (2013) Mapping procedures can produce non-centered auditory images in bilateral cochlear implantees. J Acoust Soc Am 133:EL101-7

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