Ruth Litovsky - US grants

DESCRIPTION (provided by applicant): The goal of this research is to understand how young children are able to function in complex acoustic environments, where multiple sources are often present. This includes identifying the location of sound sources, especially in noisy environments, and extracting the content meaningful sounds, such as understanding speech. This work will focus on children ages 4-7. We will measure binaural abilities using two paradigms. The first will evaluate children's ability to locate sounds, in quiet, in the presence of simulated echoes (precedence effect), and in the presence of "real world" competing sounds that are either spatially near or far from the target source. The second will focus on the children's ability to understand speech in the presence of competing speech and noise, and the extent to which they demonstrate a benefit from spatial separation of the speech and competing sounds (spatial release from masking). In adults, sound localization and spatial release from masking are known to be facilitated by the binaural system, however, surprisingly little is known about these abilities in young children. Previous work has shown that basic binaural processes are rudimentary at birth, and undergo many developmental changes during early childhood; however, the impact of these changes on children's abilities to cope with realistic complex environments remains to be understood. The long-term goal of this work is to extend our measures of auditory abilities to populations of children with sensori-neural hearing loss and with cognitive disabilities, including attention deficit disorders and autism.

[unreadable] DESCRIPTION (provided by applicant): Humans spend a majority of their time in auditory environments that are complex and reverberant. An important and ongoing task for the auditory system is the segregation of target signals from interfering sounds and the suppression of echoes. The binaural system is known to be important in accomplishing these goals. The proposed research will investigate directional hearing in multi-source and reverberant acoustic environments. We will study sound localization, suppression of echoes, and speech intelligibility, in human adults with normal hearing, and with bilaterally-implanted cochlear implant users. Aim 1 will investigate the precedence effect (PE) using more everyday paradigms than those previously employed, with speech stimuli and multiple-echo patterns that vary in number, directional properties, intensity and spectral content. In Aim 2 we will investigate the impact of these echo patterns on speech intelligibility in the presence of competing sounds whose content and spatial locations and will be varied. We will test the hypothesis that "informational masking" can be induced when listeners experience uncertainty regarding the number, content and locations of competing sounds. In Aim 3 we will study binaural mechanisms in bilateral CI users through specialized hardware that controls the binaural synchronization between the two ears. Studies will measure localization, echo suppression, speech in intelligibility in complex acoustic environments, and basic binaural processes. This research addressed fundamental issues concerning the ability of humans to function in everyday listening situations. Problems in such environments are commonly reported by hearing impaired individuals. Studies in Aim 3 might contribute to the future design of hearing aids and cochlear implants that take advantage of binaural cues and compensate for the degradation of functioning in noisy and reverberant environments. [unreadable] [unreadable] [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): The ability of hearing impaired children to function in complex multi-source environments will be studied. Children with cochlear implants (CIs) and hearing aids (HAs) spend hours every day in noisy environments such as classrooms, but their ability to hear in these environments is poorly understood. In addition, the extent to which bilateral CIs or a CI and a HA might provide a benefit compared with monaural hearing is not known. Recent thrusts by manufacturers, surgeons and parents have created a growing interest in bilateral implantation. However, this thrust must be validated with objective measures, and the tools for performing the measures must be available. This work will focus on children ages 4-10 from three groups: (1) Unilaterally implanted with a single CI, (2) Bilaterally implanted with two CIs, (3) Multi-modal with a CI in one ear and a HA in the second ear. A measurement system that can be applied in clinical setting to assess directional hearing in children rapidly and reliably, recently developed in the Pl's lab, will be employed. Computer games with puzzles and animations are implemented in order to engage the children and maintain their attention and motivation. Four specific aims are proposed with each population of children. Aim 1 will provide information regarding the potential benefits of a HA or a second CI for children's ability to detect whether a sound source is to the right or left. Aim 2 will measure the children's ability to identify source locations. Aim 3 will measure the extent to which reflections interfere with performance, which can assess the functionality of the binaural auditory pathway. Aim 4 will measure speech reception threshold (SRT) in the presence of competing sounds. This research has the potential to improve the diagnosis, selection and fitting procedures for children with hearing loss. In addition, the research might provide some insight into situations in which bilateral hearing, with dual CIs, or with a CI/HA combination, should or should not be pursued. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): The overall goal of this research is to understand how children hear in complex auditory environments. Spatial hearing, the ability to understanding speech in background noise and suppression of interference from echoes (precedence effect; PE) will be studied in children with normal hearing and in deaf children who received bilateral cochlear implants (BI-CIs). Aim 1 is to investigate the maturational progression of spatial hearing in complex acoustic environments, and the degradation that noise and echoes have on these abilities. We will test the hypothesis that spatial hearing skills are well developed early in life under simple conditions but not under complex, challenging conditions, such as when competing signals, echoes or noise are present. Aim 2 is to investigate Speech intelligibility in a multi-source environment in normal-hearing children. The decrease in masking due to spatial separation of the target and interferers (spatial release from masking; SRM) will be the focus of this work. We will test hypotheses regarding the maturation of centrally- mediated auditory abilities during childhood. Studies in Aims 1 and 2 will also provide important benchmarks for understanding the significance of bilateral benefits in children with hearing loss, and in particular for a growing population of children with bilateral cochlear implants (BI-CIs). In Aim 3, using measures from Aims 1 and 2, benefits of BI-CIs will be studied in groups of children that vary according to auditory experience prior to, and following, activation of their second implant. It is hypothesized that children with simultaneous BI-CIs will be on a quicker trajectory for emergence of bilateral benefits than children with sequential BI-CIs; that differences will be significantly diminished after 2 years of bilateral experience; that children with post- lingual deafness will perform better than those with pre-lingual deafness due to early establishment of binaural circuitry. The proposed work will help us to better understand the development of functions that are important in everyday situations. The measures developed here can be eventually implemented in clinical evaluations of amplification and fitting strategies. Findings from the BI-CI studies will provide quantitative measures of bilateral benefit in children and will be enlightening about the role of auditory plasticity and experience in a young human population. [unreadable] [unreadable] [unreadable]

ABSTRACT Cochlear implants s(CIs) provide hearing to deaf individuals by electrically stimulating the auditory nerve. Bilateral implantation has become a standard treatment in many countries, in an attempt to provide patients with auditory cues needed to segregate speech from noise and localize sounds. Despite notable benefits when listening with bilateral vs. unilateral CIs, most patients continue to perform significantly worse than normal hearing (NH) listeners. The most likely reason is the lack of synchronization of stimulation in the right and left ears. Binaural functioning in NH depends on neural coding of interaural differences in time (ITD) and level (ILD), and ILDs alone are not sufficient for producing excellent performance. Although today?s clinical processors are designed to maximize speech understanding, they do not present binaural cues to the electrode arrays in a reliable and suitable manner. We propose to investigate means for overcoming these limitations, using research interfaces that control ITDs and ILDs, with novel signal processing. Aim 1 will systematically investigate the effectiveness of novel hybrid-rate multi-channel stimulation aimed at preserving both binaural sensitivity and speech understanding. We reason that strategies that combine low-rate with high- rate stimulation engage neural mechanisms that encode both interaural timing cues (at low-rate stimulation) and envelope speech cues (at high-rate stimulation). In addition to binaural psychophysics, we will assess monaural pulse rate sensitivity as a first step towards independent assessment of neural health at each of the electrodes used in binaural stimulation. In NH listeners we will conduct novel experiments on how different hybrid rate configurations can affect overall binaural sensitivity when cues are distributed along the multiple frequency regions. The ultimate goal is to work with engineering teams that can implement these strategies in clinically fit CI processors. If successful, this approach will help to close a gap in performance that exists between CI users and NH listeners. Aim 2 will use a unique approach that measures pupil dilation (to quantify listening effort) and speech intelligibility concurrently. We will compare performance in conditions that have standard clinical listening vs. conditions aimed at improving speech intelligibility in noise and spatial release from masking. In the proposed work, our goal is to understand why patients seem to benefit from some listening strategies more than others, and more importantly to quantify the two aspects of benefit: improvement in speech intelligibility and reduced listening effort. Proposed studies are aimed at gaining insight into dimensions of real-world listening that are poorly understood. The ultimate goal is to identify binaural strategies that yield improvements across patients, so that future work can implement those strategies in a portable clinical device. In NH listeners, our proposed studies will be the first to investigate the importance of binaural cues for understanding speech in noise and listening effort.

DESCRIPTION (provided by applicant): When using a cochlear implant (CI) in one ear, children experience difficulties hearing speech in noise and localizing sounds in rooms. This is not surprising, as studies in normal hearing listeners have demonstrated that speech understanding in noise and sound localization can be very poor when binaural hearing is artificially disrupted. Inability to segregate speech from noise and to localize sounds can have a profound impact on the ability of a child to learn in environments such as classrooms, where it is typical to have multiple sounds arrive from various directions, and each child faces the challenge of segregating stimuli of interest from background noise. There has been a sweeping shift in clinical treatment, whereby bilateral CIs have become the standard of care, and 70% of bilateral CI users are children under 10 years of age. The vast majority of children perform significantly worse than their normal hearing, age-matched peers on sound localization and understanding of speech in noise. Using research processors that synchronize the CIs in the two ears, specific aims will investigate mechanisms of sound localization (Aim 1) and speech-in-noise segregation (Aim 2). In addition, we will evaluate whether peripheral measures of neural spread of excitation can serve as a useful tool for predicting binaural processing, in order to ultimately develop objective clinical tools for bilateral fitting of CIs (Aim 3). Studies will be dne in implanted children who were congenitally deaf and implanted bilaterally during infancy and children born with hearing and acquired deafness during early childhood. In addition, children with normal hearing will be studied using binaural CI simulations, in order to understand the extent to which differences between CI user and normal hearing children are accounted for by signal degradation that is known to occur with CIs. Limits imposed by the CI simulations relative to standard acoustic cues will provide a benchmark for best performance levels to be expected from the CI populations. Ultimately, the work will lead to development of better speech processors for children who are deaf, and ideally better outcomes in their ability to hear speech in noise, localize sounds, and learn in complex noisy environments.

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.