Mario A. Svirsky - US grants

This proposal aims to explore the effect of speech processing strategies that may improve speech perception by users of pulsatile cochlear implants. In addition, the proposed research aims to probe the underlying reasons for the perceptual improvements we may observe. Stimulation strategies currently used by speech processors for cochlear implants will be modified in two ways: 1) frequency-to-electrode maps will be designed to ensure tonotopicity, i.e., that electrical pulses encoding higher frequency acoustic energy are sent to electrode pairs closer to the cochlear base, and 2) stimulation rate will be substantially higher than the FO rate that is currently used. The experimental hypotheses behind these strategies are: 1) Natural spectral representation- tonotopical stimulation results in more 'natural' percepts, making it easier for users of pulsatile cochlear implants to interpret spectral acoustic cues. (2) Adequate representation of temporal cues and dynamic spectral cues- high stimulation rates (400 to 800 pulses per second as opposed to 80 to 200) will provide a better representation of fast spectral transitions, resulting in improved perception of different stop sounds in particular and improved perception of the place feature in general. In addition, these high stimulation rates will provide better representation of temporal cues, some of which (such as VOT) underlie certain voicing and manner distinctions. (3) Sufficient perceptual contrast. The ability to discriminate along acoustic continua known to be relevant in making phonetic decisions is an essential underpinning to perceptual performance. We will attempt to identify what acoustic cues underlie perceptual differences under different stimulation strategies. The proposed research includes two within-subject studies. Both studies will employ vowel and consonant confusion tests, and a words-in-sentence test. In the first study, subjects will be tested with their current maps to establish a baseline. Then they will be fitted with the new (tonotopic) maps and tested at the beginning and at the end of 2-3 weeks of tonotopic map use. Finally, they will be reprogrammed with the original map and re-tested to ensure baseline replicability. The second study will compare the best map for each patient (either their original map or the new tonotopic map) against a high-rate version of the map. Since currently available speech processors cannot implement the proposed high-rate strategies, all testing and training for this second study will be done in the laboratory, using computer-stored stimuli delivered through a special purpose interface. Confusion matrices will be analyzed using Sequential Information Transfer Analysis and log-linear modeling. In addition, stimuli will be analyzed to determine what specific electrical stimulation cues are employed by different subjects to identify speech sounds.

[unreadable] DESCRIPTION (provided by applicant): The long-term goals of this research project are to understand the mechanisms that underlie speech perception by cochlear implant (CI) users, the characteristics of auditory perceptual learning in adults, and the potential links between the two. The first specific aim of the proposed research is to develop mathematical models of phoneme and word identification for individual Cl users. We will refine and extend our models of speech perception by CI users, which are based on the users' discrimination along specified perceptual dimensions. These psychophysically-based models are explanatory:, they do not simply attempt to predict overall scores in speech perception tests, they also provide specific hypotheses about the mechanisms CI users employ to process the auditory signal to identify different speech sounds. The second specific aim of this proposal is to investigate auditory adaptation in postlingually deaf Cl users, who receive speech signals that are both spectrally degraded and shifted in frequency. We will measure the extent, time course, and possible limitations of the adaptation shown by CI users. In addition to its strong clinical interest, this specific aim is scientifically important because the CI population presents a unique opportunity to investigate adaptation to a modified frequency map, and may allow us to obtain new knowledge about central auditory system plasticity in adults. The mathematical models developed in Project I will provide one of the methods to estimate a CI user's adaptation to a mismatched frequency map. The third specific aim is to test a gradual training approach that may facilitate auditory adaptation in postlingually deaf Cl users. The gradual and standard approaches to frequency mapping in Crs will be compared using a prospective randomized double-blind trial. We will examine both CI users and normal hearing listeners; the latter will be studied while hearing an acoustic model of a CI and will participate in imaging sessions that will search for functional neurobiological correlates of the auditory learning process. If successful, this study would be an example of translational research where basic knowledge about perceptual learning and adaptation in CI users is used to design improved clinical procedures. The proposed research program spans the range from basic to clinical to applied. Insights gained from this program will advance our basic knowledge about speech perception and adaptation to changes in the peripheral frequency map, and may also result in potentially important clinical applications. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Cochlear implants (CIs) take advantage of the tonotopic structure of the cochlea, stimulating areas progressively closer to the base as the input sound frequency increases. One key fitting parameter in a CI is the frequency table wherein input acoustic frequencies are allocated to intracochlear electrodes. Under current clinical practice, all users of a given CI model receive basically the same frequency table. In postlingually hearing impaired CI users, this one-size-fits-all approach may introduce mismatches between input acoustic frequency and the characteristic frequency of the neurons that are stimulated. Although human listeners can adapt to these distortions, there is growing evidence that sometimes this adaptation process may be incomplete. Both the adaptation process and its possible incompleteness have important consequences to speech perception in the postlingually hearing impaired CI population. The first aim of the proposed work is to measure the extent and the time course of this adaptation process, which will be explored in two experiments. Experiment 1 will study recently implanted CI users and follow them for a year, using four different methods to measure adaptation to frequency mismatch, complemented by a battery of speech perception, psychophysical, cognitive, and anatomical measurements. Experiment two will examine the same questions but with a group of CI users with long term experience (at least one year). Both experiments will also have a second aim: using the anatomical and cognitive measures to predict which individuals are more likely to suffer incomplete adaptation to their clinical frequency tables. Lastly, Experiment 3 will address the third aim of the proposed research: to test the hypothesis that frequency tables intended to reduce frequency mismatch will improve speech perception scores in those CI users who show incomplete adaptation. Part of the proposed work involves developing and refining software and hardware tools to facilitate the search for alternative frequency tables that may help minimize frequency mismatch. In summary, the experiments described in this proposal will provide new insights about the nature of auditory adaptation to a modified peripheral frequency map by postlingually hearing impaired CI users, and will also provide guidance to the clinicians who are in charge of fitting these devices. Studies like the present ones will help translate basic knowledge into clinical practice, and will make clinical practice more data- and theory-driven.

DESCRIPTION (provided by applicant): There are a rapidly growing number of "bimodal" patients, people who hear using a cochlear implant in one ear and a hearing aid in the other ear. These patients hear using two different forms of sound input: the cochlear implant delivers an electrical signal and the hearing aid delivers an acoustic signal. Current clinical practice usually entails the separate fitting of each device by a different audiologist, using methods that are normally employed for standalone devices. This paradigm is based more on historical circumstances than on evidence of its effectiveness. The goal of the proposed research is to develop data-based tools that will allow clinicians to maximize bimodal speech perception by better coordinating the fitting of the hearing aid and the cochlear implant, and the post-implantation follow-up. Specific Aim 1 is to develop guidelines that will help clinicians select an appropriate hearing aid bandwidth for bimodal patients as a function of their residual hearing. Specific Aim 2 is to develop a flowchart with recommendations concerning which frequency allocation table should be used in the cochlear implant of bimodal patients as a function of their residual hearing. Specific Aim 3 is to develop guidelines for the post-implant follow up of bimodal patients, including recommendations for frequency of evaluation and conditions, tasks, and tests to be used. The set of clinical tools to be developed (lookup tables, flowcharts, and follow-up guidelines) will address a pressing clinical need and will allow clinicians to make data-driven decisions for the audiological management of bimodal patients. PUBLIC HEALTH RELEVANCE: This research will provide guidance to clinicians who manage the fitting and follow-up care of "bimodal" patients, those who use a cochlear implant in one ear and a hearing aid in the other ear. We will develop tools to help select the hearing aid and cochlear implant fittings that will provide the best bimodal speech recognition for each individual. In addition, protocols for long-term follow-up of bimodal patients will be generated.

Cochlear implants (CIs) take advantage of the tonotopic structure of the cochlea, stimulating areas progressively closer to the base as the input sound frequency increases. One key fitting parameter in a CI is the frequency table wherein input acoustic frequencies are allocated to intracochlear electrodes. Under current clinical practice, all users of a given CI model receive basically the same frequency table. In postlingually hearing impaired CI users, this one-size-fits-all approach may introduce mismatches between input acoustic frequency and the characteristic frequency of the neurons that are stimulated. Although human listeners can adapt to these distortions, there is growing evidence that sometimes this adaptation process may be incomplete. Both the adaptation process and its possible incompleteness have important consequences to speech perception in the postlingually hearing impaired CI population. The first aim of the proposed work is to measure the extent and the time course of this adaptation process, which will be explored in two experiments. Experiment 1 will study recently implanted CI users and follow them for a year, using four different methods to measure adaptation to frequency mismatch, complemented by a battery of speech perception, psychophysical, cognitive, and anatomical measurements. Experiment two will examine the same questions but with a group of CI users with long term experience (at least one year). Both experiments will also have a second aim: using the anatomical and cognitive measures to predict which individuals are more likely to suffer incomplete adaptation to their clinical frequency tables. Lastly, Experiment 3 will address the third aim of the proposed research: to test the hypothesis that frequency tables intended to reduce frequency mismatch will improve speech perception scores in those CI users who show incomplete adaptation. Part of the proposed work involves developing and refining software and hardware tools to facilitate the search for alternative frequency tables that may help minimize frequency mismatch. In summary, the experiments described in this proposal will provide new insights about the nature of auditory adaptation to a modified peripheral frequency map by postlingually hearing impaired CI users, and will also provide guidance to the clinicians who are in charge of fitting these devices. Studies like the present ones will help translate basic knowledge into clinical practice, and will make clinical practice more data- and theory-driven.

DESCRIPTION (provided by applicant): There are a rapidly growing number of bimodal patients, people who hear using a cochlear implant in one ear and a hearing aid in the other ear. These patients hear using two different forms of sound input: the cochlear implant delivers an electrical signal and the hearing aid delivers an acoustic signal. Current clinical practice usually entails the separate fitting of each device by a different audiologist, using methods that are normally employed for standalone devices. This paradigm is based more on historical circumstances than on evidence of its effectiveness. The goal of the proposed research is to develop data-based tools that will allow clinicians to maximize bimodal speech perception by better coordinating the fitting of the hearing aid and the cochlear implant, and the post-implantation follow-up. Specific Aim 1 is to develop guidelines that will help clinicians select an appropriate hearing aid bandwidth for bimodal patients as a function of their residual hearing. Specific Aim 2 is to develop a flowchart with recommendations concerning which frequency allocation table should be used in the cochlear implant of bimodal patients as a function of their residual hearing. Specific Aim 3 is to develop guidelines for the post-implant follow up of bimodal patients, including recommendations for frequency of evaluation and conditions, tasks, and tests to be used. The set of clinical tools to be developed (lookup tables, flowcharts, and follow-up guidelines) will address a pressing clinical need and will allow clinicians to make data-driven decisions for the audiological management of bimodal patients.

PROJECT SUMMARY The human auditory brain is remarkably plastic but we still do not know just how plastic it is, particularly when it comes to higher cognitive functions like speech perception and music enjoyment. These are uniquely human skills which are difficult (if not impossible) to study in animal models. Post-lingually hearing impaired cochlear implant (CI) users have provided a very interesting platform to study plasticity in response to auditory stimuli sent to a non-standard peripheral frequency-place function. This is because the frequency-place function imposed by a CI is different for each individual (due to differences in cochlear size, electrode location, and neural survival patterns) and can be quite different from the ?natural?, physiological frequency-place function. This proposal seeks to investigate auditory plasticity in traditional post-lingually hearing impaired CI users (Aims 1 and 2) as well as in a novel population of CI users who have normal hearing in the unimplanted ear (Aims 3 and 4). This new clinical population of CI users with single-sided deafness (CI-SSD) is ideal to study adaptation to frequency-place functions without the confounds that complicate interpretation of results in listeners with partial or complete deafness. In Aim 1 we will study the combined effect of using electrode selection and listener-selected frequency allocation tables (FATs) in postlingually hearing impaired CI users. There are indications that these two interventions (both of which affect the frequency-place function in different ways) may enhance speech perception and sound quality. In Aim 2 we will test the use of a smartphone-based app to facilitate the selection of customized frequency-place functions in the real world rather than in the acoustically controlled environment of a laboratory or a clinic. In Aim 3 we will use three behavioral tests of adaptation to frequency- place functions in CI-SSD patients. Data from one of these tests will allow us to meet an important sub-aim: to assess the validity of existing acoustic models of cochlear implantation, and to create improved acoustic models whose sound quality and speech intelligibility are similar to those obtained with a CI. Lastly, in Aim 4 we will study the effect of user-selected frequency-place functions on bilateral music sound quality and bilateral unmasking, also in CI-SSD patients. The proposed experiments will yield novel and unique information about how postlingually hearing impaired humans adapt to modified frequency-place functions, and thus will make an important contribution to studying basic auditory function in humans. We believe that the proposed research also has important translational implications that are likely to influence clinical practice as well as research with CI users.

1) Project Summary/Abstract Cochlear prosthesis is widely accepted as the most effective clinical intervention to restore auditory function of individuals with profound hearing loss. Although state-of-the-art CIs provide a high level of speech comprehension and aural communication ability to a majority of implant recipients, there remains a major gap between performance levels of CI users and normal hearing individuals, especially in real-life noisy environments. This gap in performance in part can be attributed to limitations in both sound coding and electrical stimulation strategies, and partially due to the limited ability to explore potentially new advanced algorithms with current CI users in the field. Several methods have been proposed over the years to address this shortcoming; however, most have been restricted to laboratory research. This is primarily due to the unavailability of portable sound processing platforms that can 1) implement computationally-intensive sound processing schemes and 2) assess them chronically in real naturalistic environments. Clinical processors/platforms are neither powerful, nor flexible to meet the growing scientific needs of the research community. We propose a multi-center research effort to investigate three complementary sound processing strategies (Aims 1 ? 3), which will be made possible through the proposed research platform (Aim 4). First, we will develop and test the effectiveness of two new families of front-end speech processing algorithms (Aim 1), both of which are inspired by speech production/perception physiology and aim to enhance the speech signal from competing background noise. The potential benefit of these algorithms in real-life acoustic environments will be assessed by conducting take-home trials using the portable research platform. Next, we will investigate the potential benefits of real-time user-specified adjustments to frequency allocation and stimulation rate adjustments on speech perception and sound quality in naturalistic environments (Aim 2). In Aim 3, we will investigate the effectiveness of speech processing strategies that deliver synchronized electrical stimulation to bilateral CIs. Specifically, we aim to test differences in ITD discrimination, sound localization, and segregation of speech in noise with and without synchronized bilateral stimulation. These studies will be done using the existing prototype of the platform, CCi-MOBILE. As a next step we propose to develop a next-generation CCi- MOBILE-2 platform - a flexible, open-source, portable sound processing platform that will allow easy implementation of research ideas as well as long-term assessments of algorithms in real-life acoustic environments (Aim 4). This one-of-a-kind research platform will be orders of magnitude more flexible and computationally powerful than existing clinical processors and will aid in bridging scientific research with commercial applications. The CCi-MOBILE-2 platform will be shared with the CI research community free of cost using an open source model. The experiments listed here represent a mere subset of the potential groundbreaking advancements that will be made possible by the existence of the proposed research platform. The ability to perform real-life chronic speech assessments will open new frontiers for scientific exploration and will result in a paradigm shift in how speech processing/perception research is carried out in the cochlear implant field. Advancements from Aims 1-3 will show clear examples of how to transition scientific and algorithmic advancements to field testing with the CCi-MOBILE-2 (Aim 4), thus giving operational examples on how to leverage the research platform for other research laboratories.

PROJECT SUMMARY Older adults are the fastest growing segment of the U.S. population, with hearing loss the third most prevalent chronic medical condition. Untreated, hearing loss can interfere with effective communication, quality of life, and potentially accelerate cognitive decline. Cochlear implants (CI) have seen increasing use for older adults, with one implant center reporting a nearly 500% increase over a recent ten-year period in the number of individuals aged 60 or older receiving CIs. The auditory input provided by a CI is sharply degraded with respect to that of a person with normal hearing or even with mild to moderate hearing loss, but patients can adapt well to this novel input- at least when measured by standard clinical tests of word identification (e.g., CNC words) or perception of simple sentences (e.g., AzBio sentences). However, clinicians are often puzzled by patients, especially older adults, who seem to do well on standard tests but report major difficulties in everyday speech interactions. This grant builds upon the hypothesis that the combined constraints of the sharply degraded signal provided by a CI and finite cognitive resources may lead to a ?tipping point? when listeners are confronted with complex sentences and discourse arriving at normally rapid speech rates. Beyond this tipping point communication may become too difficult, even for CI recipients whose standard speech intelligibility scores are above average. This grant brings together a unique combination of three converging approaches: (1) We examine the ability of younger adult and older adult CI users to comprehend and remember the content of linguistically complex sentences and multi-sentence discourse, and probe potential effects on the cognitive mechanisms listeners use to process speech input, an underlying issue as yet unexplored in CI research; (2) For each experiment we will conduct a parallel study with normal-hearing younger and older adults using channel vocoded and unprocessed speech, with the former allowing a systematic determination of the interaction between signal degradation and the complexity of the speech materials on their recall, and the latter to illustrate a baseline of optimal performance on the same tasks for age-matched adults; (3) We will use modern pupillometry measures as an objective index of cognitive effort time-locked to the content of the speech input. The knowledge gained will test current models of resource allocation and listening effort as mechanisms underlying effects of cognitive load when younger and older adult CI users face the natural complexity of everyday sentences and discourse. Results of the studies will be valuable for counseling CI recipients and their families and will help develop more comprehensive evaluation batteries and rehabilitative strategies for the older adult CI recipient.