Otology & Neurotology - ACIA: Highlights from the 14th International Symposium on Cochlear Implants, Toronto, Canada

Introduction to the 14th International Symposium on Cochlear Implants and other Implantable Auditory Technologies, Toronto, Canada, May 11 to 14, 2016 No abstract available

Physiological Mechanisms in Combined Electric–Acoustic Stimulation Objective: Electrical stimulation is normally performed on ears that have no hearing function, i.e., lack functional hair cells. The properties of electrically-evoked responses in these cochleae were investigated in several previous studies. Recent clinical developments have introduced cochlear implantation (CI) in residually-hearing ears to improve speech understanding in noise. The present study documents the known physiological differences between electrical stimulation of hair cells and of spiral ganglion cells, respectively, and reviews the mechanisms of combined electric and acoustic stimulation in the hearing ears. Data Sources: Literature review from 1971 to 2016. Conclusions: Compared with pure electrical stimulation the combined electroacoustic stimulation provides additional low-frequency information and expands the dynamic range of the input. Physiological studies document a weaker synchronization of the evoked activity in electrically stimulated hearing ears compared with deaf ears that reduces the hypersynchronization of electrically-evoked activity. The findings suggest the possibility of balancing the information provided by acoustic and electric input using stimulus intensity. Absence of distorting acoustic–electric interactions allows exploiting these clinical benefits of electroacoustic stimulation.

NANOCI—Nanotechnology Based Cochlear Implant With Gapless Interface to Auditory Neurons Cochlear implants (CI) restore functional hearing in the majority of deaf patients. Despite the tremendous success of these devices, some limitations remain. The bottleneck for optimal electrical stimulation with CI is caused by the anatomical gap between the electrode array and the auditory neurons in the inner ear. As a consequence, current devices are limited through 1) low frequency resolution, hence sub-optimal sound quality and 2), large stimulation currents, hence high energy consumption (responsible for significant battery costs and for impeding the development of fully implantable systems). A recently completed, multinational and interdisciplinary project called NANOCI aimed at overcoming current limitations by creating a gapless interface between auditory nerve fibers and the cochlear implant electrode array. This ambitious goal was achieved in vivo by neurotrophin-induced attraction of neurites through an intracochlear gel-nanomatrix onto a modified nanoCI electrode array located in the scala tympani of deafened guinea pigs. Functionally, the gapless interface led to lower stimulation thresholds and a larger dynamic range in vivo, and to reduced stimulation energy requirement (up to fivefold) in an in vitro model using auditory neurons cultured on multi-electrode arrays. In conclusion, the NANOCI project yielded proof of concept that a gapless interface between auditory neurons and cochlear implant electrode arrays is feasible. These findings may be of relevance for the development of future CI systems with better sound quality and performance and lower energy consumption. The present overview/review paper summarizes the NANOCI project history and highlights achievements of the individual work packages.

Cochlear Implants Meet Regenerative Biology: State of the Science and Future Research Directions The cochlear implant, the first device to restore a human sense, is an electronic substitute for lost mechanosensory hair cells. It has been successful at providing hearing to people with severe to profound hearing loss and as of 2012, an estimated 324,000 patients worldwide have received cochlear implants. Users of cochlear implants however, suffer from difficulties in processing complex sounds such as music and in discriminating sounds in noisy environments. Recent advances in regenerative biology and medicine are opening new avenues for enhancing the efficacy of cochlear implants by improving the neural interface in the future and offer the possibility of an entirely biological solution for hearing loss in the long term. This report comprises the latest developments presented in the first Symposium on cochlear implants and regenerative biology, held at the 14th International Conference on Cochlear Implants in 2016 in Toronto, Canada.

Linking Deafness and Dementia: Challenges and Opportunities The rising incidence of dementia locally and worldwide has now reached a critical level. The associated costs associated with these individuals will ultimately be untenable to most societies. Furthermore there is a paucity of highly effective treatments. However, the recent discovery of the association of hearing loss and dementia may open many potential opportunities. Although we still are acquiring knowledge on the pathophysiology of this association, clinicians are hopeful that our current highly effective treatments of hearing loss may ultimately be shown to have a positive effect on those with dementia.

What Does Music Sound Like for a Cochlear Implant User? Objective: Cochlear implant research and product development over the past 40 years have been heavily focused on speech comprehension with little emphasis on music listening and enjoyment. The relatively little understanding of how music sounds in a cochlear implant user stands in stark contrast to the overall degree of importance the public places on music and quality of life. The purpose of this article is to describe what music sounds like to cochlear implant users, using a combination of existing research studies and listener descriptions. We examined the published literature on music perception in cochlear implant users, particularly postlingual cochlear implant users, with an emphasis on the primary elements of music and recorded music. Additionally, we administered an informal survey to cochlear implant users to gather first-hand descriptions of music listening experience and satisfaction from the cochlear implant population. Conclusion: Limitations in cochlear implant technology lead to a music listening experience that is significantly distorted compared with that of normal hearing listeners. On the basis of many studies and sources, we describe how music is frequently perceived as out-of-tune, dissonant, indistinct, emotionless, and weak in bass frequencies, especially for postlingual cochlear implant users—which may in part explain why music enjoyment and participation levels are lower after implantation. Additionally, cochlear implant users report difficulty in specific musical contexts based on factors including but not limited to genre, presence of lyrics, timbres (woodwinds, brass, instrument families), and complexity of the perceived music. Future research and cochlear implant development should target these areas as parameters for improvement in cochlear implant-mediated music perception.

Cochlear Implantation in Postlingual Adult Patients With Long-Term Auditory Deprivation Objective: The role of long-term hearing deprivation in cochlear implant performance is not well established, and the limits for implanting an auditory deprived ear are still unknown. The objective of this study was to evaluate the effect of long-term auditory deprivation time on cochlear implant results. Study Design: Retrospective case review study. Setting: Cochlear implantation tertiary referral center. Patients: Adult patients with postlingual deafness. Intervention: Unilateral cochlear implantation between 2001 and January 2015. Main Outcome Measures: Age at implantation, sex, etiology of hearing loss, and duration of auditory deprivation in the implanted ear were collected. Cochlear implants results were expressed in terms of vowel identification, disyllabic word recognition, and sentence recognition. Spearman's correlation test was applied to determine the relationship between auditory deprivation time and speech recognition scores. Additionally, patients were divided according to their auditory deprivation time before implantation in group A (less than 10 yr) and group B (more than 10 yr). Results: One hundred three patients met inclusion criteria for this study. There were 61 patients in group A, with a mean deprivation time of 2.52 years. There were 42 patients in group B, with a mean deprivation time of 19.67 years. There were no statistically significant differences between both groups regarding speech recognition scores. Deprivation time in the implanted ear was not statistically correlated with cochlear implantation performance. Conclusions: Long-term auditory deprivation in the ear to be implanted does not negatively influence cochlear implantation results and should not be considered criterion to reject cochlear implantation.

A Smartphone Application for Customized Frequency Table Selection in Cochlear Implants Hypothesis: A novel smartphone-based software application can facilitate self-selection of frequency allocation tables (FAT) in postlingually deaf cochlear implant (CI) users. Background: CIs use FATs to represent the tonotopic organization of a normal cochlea. Current CI fitting methods typically use a standard FAT for all patients regardless of individual differences in cochlear size and electrode location. In postlingually deaf patients, different amounts of mismatch can result between the frequency-place function they experienced when they had normal hearing and the frequency-place function that results from the standard FAT. For some CI users, an alternative FAT may enhance sound quality or speech perception. Currently, no widely available tools exist to aid real-time selection of different FATs. This study aims to develop a new smartphone tool for this purpose and to evaluate speech perception and sound quality measures in a pilot study of CI subjects using this application. Methods: A smartphone application for a widely available mobile platform (iOS) was developed to serve as a preprocessor of auditory input to a clinical CI speech processor and enable interactive real-time selection of FATs. The application's output was validated by measuring electrodograms for various inputs. A pilot study was conducted in six CI subjects. Speech perception was evaluated using word recognition tests. Results: All subjects successfully used the portable application with their clinical speech processors to experience different FATs while listening to running speech. The users were all able to select one table that they judged provided the best sound quality. All subjects chose a FAT different from the standard FAT in their everyday clinical processor. Using the smartphone application, the mean consonant–nucleus–consonant score with the default FAT selection was 28.5% (SD 16.8) and 29.5% (SD 16.4) when using a self-selected FAT. Conclusion: A portable smartphone application enables CI users to self-select frequency allocation tables in real time. Even though the self-selected FATs that were deemed to have better sound quality were only tested acutely (i.e., without long-term experience with them), speech perception scores were not inferior to those obtained with the clinical FATs. This software application may be a valuable tool for improving future methods of CI fitting.

Musical Rehabilitation in Adult Cochlear Implant Recipients With a Self-administered Software Objective: The goal of this study was to determine if a self-administered computer-based rehabilitation program could improve music appreciation and speech understanding in adults who have a cochlear implant (CI). Study Design: Prospective study. Setting: Tertiary adult CI program. Patients: Twenty-one postlingually deafened cochlear implant users between the ages of 27 and 79 years were recruited. Interventions(s): A self-administered music rehabilitative software was designed to help improve the perception of musical patterns of increasing complexity, as well as pitch and timbre perception, premised on focused and divided attention. All participants completed a diagnostic music test before and after rehabilitative training, including tests of pitch and timbre perception and pattern identification with increasing levels of difficulty. Speech data in quiet and noise was also collected both pre- and post-training. Participants trained for a minimum of 3.5 hours a week, for 4 weeks. Main Outcome Measure(s): Mean changes in music perception and enjoyment as well as speech perception (IEEE sentence test in quiet and noise). Results: Post-training diagnostic test scores, as compared with pretraining scores, indicated significant improvements in musical pattern perception. Tests of speech perception in quiet and in noise were significantly improved in a subset of this cohort. All of the training participants thought that the training helped to improve their recognition skills, and found the program to be beneficial. Conclusion: Despite the limitations of current CI technology, the results of this study suggest that auditory training can improve music perception skills, and possibly speech intelligibility, lending further support to rehabilitation being an integral part of the postimplantation paradigm.

The Sound Quality of Cochlear Implants: Studies With Single-sided Deaf Patients Objective: The goal of the present study was to assess the sound quality of a cochlear implant for single-sided deaf (SSD) patients fit with a cochlear implant (CI). Background: One of the fundamental, unanswered questions in CI research is "what does an implant sound like?" Conventional CI patients must use the memory of a clean signal, often decades old, to judge the sound quality of their CIs. In contrast, SSD-CI patients can rate the similarity of a clean signal presented to the CI ear and candidate, CI-like signals presented to the ear with normal hearing. Methods: For Experiment 1 four types of stimuli were created for presentation to the normal hearing ear: noise vocoded signals, sine vocoded signals, frequency shifted, sine vocoded signals and band-pass filtered, natural speech signals. Listeners rated the similarity of these signals to unmodified signals sent to the CI on a scale of 0 to 10 with 10 being a complete match to the CI signal. For Experiment 2 multitrack signal mixing was used to create natural speech signals that varied along multiple dimensions. Results: In Experiment 1 for eight adult SSD-CI listeners, the best median similarity rating to the sound of the CI for noise vocoded signals was 1.9; for sine vocoded signals 2.9; for frequency upshifted signals, 1.9; and for band pass filtered signals, 5.5. In Experiment 2 for three young listeners, combinations of band pass filtering and spectral smearing lead to ratings of 10. Conclusion: The sound quality of noise and sine vocoders does not generally correspond to the sound quality of cochlear implants fit to SSD patients. Our preliminary conclusion is that natural speech signals that have been muffled to one degree or another by band pass filtering and/or spectral smearing provide a close, but incomplete, match to CI sound quality for some patients.

Alexandros Sfakianakis
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alsfakia@gmail.com