Lina A. Reiss, Ph.D. - US grants

The goal of this thesis proposal is to elucidate the function of auditory neurons in the cochlear nucleus (CN) and central nucleus of the inferior colliculus (CNIC). A first step toward understanding function is to find out what stimuli the neuron responds to, ideally without a priori assumptions. Thus, Aim 1 is to develop a method for estimating the spectrotemporal weighting functions (STWFs) of single auditory neurons with pseudorandom noise stimuli. The STWF, or weights that a neuron assigns to sound energy at certain times and frequencies, can be directly applied to predict linear, or nearly linear, neural responses to arbitrary stimuli. Aim 2 is to estimate the STWFs of neurons in the CN of the decerebrate cat, and use local injection of agents that block inhibitory inputs to determine how these STWFs are shaped by inhibition. Aim 3 is to extend the method to include binaural spectrotemporal interactions when estimating weighting functions in the CNIC of the decerebrate cat. Together, experiments of these aims will increase understanding of circuitry and function in the CN and CNIC, and will in turn suggest how hearing impairment and other auditory disorders affect processing of speech and other complex sounds.

[unreadable] DESCRIPTION (provided by applicant): Summary: Three sets of experiments are proposed that address clinically relevant questions for cochlear implant patients, especially those who have and will receive the Hybrid (short-electrode) cochlear implant. The Hybrid is implanted only into the high-frequency region of the cochlea, but speech information provided through the implant is often from a lower frequency range not necessarily matched to the cochlear frequencies being stimulated. Preliminary data indicates that the pitch associated with stimulation to these basal electrodes can, for some patients, change dramatically over time to a much lower pitch sensation. The information obtained will increase understanding of how auditory perception can adjust to this spectrally shifted frequency-place information from cochlear implants, and how this relates to speech perception performance with the implant. Specifically, the project will: 1) measure pitch sensations in Hybrid cochlear implant users at various times from "hookup" up to 4 years of implant use, to determine if pitch sensations change over time; 2) test whether changing the speech processor frequency range causes pitch sensations to change, to compensate for the spectral shift of the speech; and 3) correlate speech perception performance with pitch sensations at various times, to determine how speech perception relates to pitch sensation. Relevance: The proposed research will study how much pitch perception changes over time, as a result of experience with hearing sounds through a cochlear implant, and whether perceived pitch can be a predictor of future speech understanding with the implant. These findings will have implications for how much the design of neural prostheses can be evaluated based on perceptual responses, which may be altered over time by experience. [unreadable] [unreadable] [unreadable] [unreadable]

Project Summary Approximately 22 million Americans have a hearing impairment. While hearing devices such as hearing aids (HAs) and cochlear implants (CIs) are successful in improving speech recognition for many hearing- impaired individuals, there is still significant variability in benefit, and speech recognition in noise remains a problem. One factor that may limit benefit, especially binaural benefit, is abnormal binaural spectral integration. A prerequisite for binaural integration is binaural fusion ? the fusion of stimuli from the two ears into a single auditory object. Our findings from the previous grant showed that unlike normal-hearing (NH) listeners, many HA and CI users experience abnormally ?broad? binaural fusion in the spectral domain, such that pitches that differ greatly in frequency between the two ears are still heard as a single percept. Individuals with broad fusion also experience abnormal binaural spectral integration - averaging and thus distortion of spectral information across the ears when disparate sounds are fused. We also showed broad fusion to be associated with binaural interference ? poorer speech recognition with two ears compared to one. More importantly, preliminary data show that broad fusion is associated with greater difficulty with understanding speech in challenging multi-talker listening situations, such as noisy restaurants. Difficulties with speech understanding in noise is a major complaint of both HA and CI users. In order to help hearing-impaired listeners reduce binaural interference and improve speech understanding in background noise, we need to understand the underlying causes and factors in broad fusion. The long-term goal of this research program is to investigate the effects, causes, and potential treatments for abnormal binaural spectral integration in hearing-impaired listeners. In this proposal we will: 1) determine how broad binaural fusion affects speech perception in quiet and in background talkers; and 2) investigate potential causes of broad binaural fusion in children and adults with HAs and CIs, focusing on peripheral spectral resolution, auditory experience, and top-down auditory processing factors. The proposed research will indicate the role of broad binaural spectral fusion in difficulties faced by hearing-impaired listeners, especially for speech understanding in background noise. Determination of the factors underlying broad fusion will inform future rehabilitation approaches to treat broad fusion, and help hearing-impaired listeners attain the same benefits of binaural hearing as NH listeners.

DESCRIPTION (provided by applicant): Approximately 22 million Americans have a hearing impairment. While hearing devices such as hearing aids (HAs) and cochlear implants (CIs) are successful in improving speech recognition for many hearing-impaired (HI) individuals, there is still significant variability in benefit, and speech recognition in noise remains a problem. One factor that may limit benefit is interference between bilaterally worn hearing devices, whether the devices are bilateral HAs, bilateral CIs, or a unilateral CI worn with a HA in the contralatera ear (bimodal CI+HA). In HI individuals, spectral information is not necessarily matched between ears due to asymmetries introduced by hearing loss and hearing device programming. Thus, unlike normal-hearing (NH) listeners, HI listeners integrate mismatched spectral information between ears, in a process that we can call binaural spectral integration (BSI). Our preliminary studies suggest that BSI adapts to reduce perception of interaural spectral mismatch in HI individuals; binaural fusion is increased so that pitches that differ greatly in frequency between the two ears are still heard as a single percept. However, a side effect of increased binaural fusion is that mismatched spectral information is averaged between ears, which may lead to increased speech perception confusions and worsened frequency discrimination. The long-term goal of this research program is to investigate how BSI differs between HI and NH listeners, and the clinical implications of these differences for rehabilitation. Specifically, in this proposal w will examine 1) differences in binaural fusion between HI and NH listeners, as well as across different device combinations within the HI group: bilateral HAs, bilateral CIs, and bimodal CI+HA; 2) how abnormal BSI affects the perception of tone and speech stimuli; and 3) how BSI changes as children develop, because developing brains may adapt BSI differently than adults. The proposed research will increase our understanding of how one aspect of auditory processing, binaural spectral integration, contributes to difficulties with binaural speech perception in HA and CI users. The results will also indicate whether hearing devices should be programmed differently for children than adults. Finally, the results will build the theoretical framework for future planned studies using frequency-specific device programming and training programs to reduce any detrimental BSI, while maintaining or increasing the benefits of binaural processing for speech perception in quiet and noise.

Project Summary Approximately 22 million Americans have a hearing impairment. Cochlear implants (CIs), a neural prosthesis developed to treat severe hearing loss, have significantly improved speech understanding in quiet for many individuals with hearing loss. However, benefit remains highly variable across the patient population, and speech understanding in noise remains a problem. A recent advance is the Hybrid or Electro-Acoustic Stimulation (EAS) CI, which is shorter and thinner than a traditional CI, and together with soft surgery techniques enables preservation of hearing in the implanted ear. This allows combined electric and acoustic stimulation (EAS) in the same ear, which dramatically improves speech perception in noise, voice recognition, and musical melody and timbre recognition. However, currently 30-55% of EAS CI recipients lose more than 30 dB of hearing after implantation, which can negate these benefits. Thus, post-surgical hearing preservation rates need to be improved to improve outcomes for EAS CIs. In order to improve hearing preservation, we need to understand the mechanisms of post-implantation hearing loss. Our preliminary studies indicate one likely mechanism of hearing loss: surgical trauma may reduce the blood supply to the lateral wall of the cochlea essential for maintaining the endocochlear potential necessary for hearing. Alternatively, inflammation in response to the surgery or the presence of the electrode may decrease ion homeostasis or compromise the integrity of the blood-labyrinth barrier in the lateral wall which are both necessary for maintaining the endocochlear potential. In this proposal, we will examine the role of endocochlear potential loss and lateral wall changes in hearing loss. The long-term goal of this research program is to investigate how cochlear implantation affects hearing. The findings will be highly clinically significant for building a mechanism-based framework for the design of future treatments and strategies to reduce hearing loss and improve outcomes with cochlear implants.

Project Summary Approximately 22 million Americans have a hearing impairment. Cochlear implants (CIs), a neural prosthesis developed to treat severe hearing loss, have significantly improved speech understanding in quiet for many individuals with hearing loss. However, benefit remains highly variable across the patient population, and speech understanding in noise remains a problem. A recent advance is the Electro-Acoustic Stimulation (EAS) CI, which allows combined electric and acoustic stimulation in the same ear. EAS dramatically improves speech perception in noise, voice recognition, and musical melody recognition. These benefits are proportional to the amount of residual hearing preserved after cochlear implantation. However, 30-55% of EAS CI recipients lose more than 30 dB of residual hearing after implantation, which can negate these benefits. In addition, increased age is associated with greater hearing loss. In order to improve hearing preservation and EAS outcomes, we need to understand the mechanisms of post-implantation hearing loss. Hearing preservation may also improve outcomes for the general CI population. Traditional CI users with hearing preservation have better outcomes even with just the CI alone, suggesting a relationship between hearing preservation and effectiveness of electrical stimulation. In order to improve CI outcomes for all patients, it is critical to understand how and why CI performance is related to residual hearing preservation. In this proposal, we will investigate 1) the potential mechanisms of hearing loss after implantation, and the interaction with age; and 2) the impact of this hearing loss on electrical stimulation with the CI. The findings will guide the selection of more targeted drugs or treatments that improve hearing preservation and general outcomes with CIs.