University of Maryland
Neural adaptation in new hearing aid users

Hearing loss is among the top three chronic health conditions of senior citizens, affecting approximately 50% of the population > 65 years. Despite this high prevalence of hearing loss, only 20% of senior citizens with hearing loss use a hearing aid. Why do senior citizens reject hearing aids after trying them, despite available advances in hearing aid technology? One possibility is that current hearing aid fitting practices focus on providing adequate volume but do not take into account what happens to the amplified signal as it travels along the brain’s pathways. Aging and hearing loss can have a detrimental effect on the brain’s sound processing, and at this time, we don’t understand the impact of hearing aid use on sound processing. Furthermore, the brain’s responses to amplified sound may change over the course of time to the extent that hearing aid settings may need to be re-adjusted. This study compares brainstem and cortical-evoked electroencephalographic responses to speech with and without hearing aids in individuals who have never worn hearing aids, and then evaluates changes in the brain’s responses to amplified speech over the course of 6 months. This information should help hearing aid program designers and audiologists to optimize the hearing aid fitting.

Click to download a PDF of Dr. Bartlett’s Meet the Researcher profile.

Massachusetts General Hospital
A systems approach to characterization of subcortical and cortical contributions to temporal processing deficits in central auditory processing disorders

Increasingly in the clinic, children report difficulty in understanding speech in the presence of other competing sounds. When these children are able to detect faint tones normally and show no classic signs of other neurological disorders, they are labeled as having Central Auditory Processing Disorder (CAPD). Understanding speech in a noisy setting is complex and relies both on the representation of subtle sound features by the auditory system, and the brain’s ability to make use of this information. Thus, difficulty can arise for a variety of reasons. Indeed, difficulty communicating in noisy settings is reported in a wide range of diagnostic categories such as Language Delays, Autism Spectrum Disorders, and Dyslexia among others. Yet, robust diagnostics that characterize CAPD – an auditory-specific disorder – as distinct from these other disorders are lacking. Here, we will use otoacoustic emissions and non-invasive brain imaging techniques (Electro/Magnetoencephalography) to passively measure how children’s inner ear, brainstem and cortex capture sound information. By examining the relationship between these measures and listening behavior, we aim to obtain a detailed objective test battery for the assessment of auditory function that would lead to novel clinical diagnostics for CAPD and provide clues for targeted intervention.

Rochester Institute of Technology
Auditory Experience, Critical Periods, and the Development of Categorical Perception in Cochlear Implant Users: A Preliminary Investigation

My project will investigate the role of age on the success of cochlear implantation and auditory experience on the development of perceptual (phoneme) categories in prelingually deaf cochlear implant users. The research will demonstrate the degree to which these cochlear implant users can categorize speech sounds, which will improve our understanding of speech perception and the effects of early auditory deprivation on the overall success of cochlear implantation.

University of Colorado - Boulder
Toddlers’ and preschoolers’ ability to hear speech in noise: Assessing performance with a two-interval, observer-based procedure

Children require access to acoustic information in order to develop speech and language. However, this information is often degraded because of competing sounds in the environment. While it is clear that children’s ability to listen in noise substantially improve between infancy and entering school, we do not know how and when this process unfolds during the intervening years.

The objective of this project is to develop a reliable behavioral method for measuring speech perception in noise for toddlers and preschoolers. This approach will build upon a recently developed testing method, in which a child’s behavior is judged by an experimenter using a two-interval, two-alternative testing paradigm . The children’s response to the stimulus is further shaped by training them to perform a conditioned play-based response to the sound. The proposed research will test the hypotheses that reliable data can be collected from toddlers and preschoolers and that speech-in-noise abilities improve dramatically during this time period. Results from this project will provide us information on how typical auditory development unfolds during the toddler and preschooler years, which may advance our understanding of the potential underpinnings of auditory processing disorders and the effects of hearing loss.

University of Iowa
Neural correlates of selective listening deficits in a multiple-speaker environment

Choi’s lab studies how human brains understand speech in noisy everyday settings, how central brain functions are affected by hearing loss, and how we can improve hearing-related brain functions with training.

This study will investigate several key neural processing systems required for successful speech communication in noisy social settings, and how neural processing deteriorates in listeners with degraded hearing ability. As such the project involves basic neuroscientific research of the central auditory system and translational research on hearing rehabilitation techniques.

Massachusetts Eye and Ear Infirmary
Restoring binaural hearing with cochlear implants in early-onset deafness

Many profoundly deaf people wearing cochlear implants still face challenges in everyday situations such as understanding conversations in crowds. This is because, even with cochlear implants in both ears, they have difficulty making full use of subtle differences in the sounds reaching two ears to identify where the sound is coming from. This problem is especially acute in children with congenital deafness. We will study how perceptual training can help the brain to develop the circuitry for processing this precise information in animals with early-onset deafness. Results from the study will eventually lead to new sound processors and rehabilitation strategies specifically adapted for bilateral cochlear implants.

Research area: neural coding of cochlear implant stimulation, central auditory plasticity

Long-term goal of research: To improve treatments for children with early-onset deafness by studying how neural mechanisms for binaural processing are altered by auditory deprivation during development and whether these effects can be reversed by CI stimulation.

Texas Christian University
Lateralization of acoustic perception in Bengalese finches

Cooper’s research aims to further our understanding of how different sides of the brain are specialized for processing different frequencies of sounds. Auditory processing of speech and language is lateralized to the left hemisphere of the human brain. Cooper’s specific aims are to determine whether auditory processing in the Bengalese finch is lateralized to specific sides of the brain, as in humans, and to determine whether the lateralization is learned or genetically determined.

Research area: Central Auditory Processing Disorder

Long-term goal of research: To develop this animal model for testing and refining treatments for hearing loss and lateralized frequency processing deficits in humans, including CAPD.

Cincinnati Children's Hospital Medical Center
Sensory and Cognitive Processing in Children with Auditory Processing Disorders: Behavior and Electrophysiology

Central Auditory Processing Disorder (CAPD) can be defined as having a listening difficulty despite having normal hearing. One theory of CAPD is that this bottom-up processing isn’t working properly, a bit like listening to a de-tuned radio or TV. However, when the sound code reaches the cortex, it is mixed with a variety of signals from other systems, including vision, memory and attention. A second theory of CAPD is that the problem occurs at this level of mixing. In this ‘top-down’ theory, inappropriate control signals from high-level thinking systems, especially memory and attention, are thought to lead to misunderstanding of the code produced in the auditory system. Unfortunately, these two theories are difficult to tease apart. For example, a typical statement by a parent of a child with CAPD is that (s)he seems unaware when being spoken to. This could indicate poor listening due to inattention, or due to an inability to process speech sounds in the auditory system. Understanding which theory is correct may be important for treatment of CAPD. This research aims to tease apart these two theories by examining how the brain processes sound. One aspect of this research will examine how the brain encodes pitch and level fluctuations in sound. Both of these sound qualities are the “building blocks” of speech. If there are deficits at this level of neural processing then perhaps a “bottom up” or sound encoding problem exists. Another aspect of this research will examine a more cognitive approach and examine how the brain deals with speech in noise. This will be indexed by use of brain oscillations which are thought to reflect neural networks across different parts of the brain. Therefore by approaching CAPD from these two directions, it may be possible to show whether their listening difficulties are due to bottom-up or top-down processing problems.

Albert Einstein College of Medicine
Effects of aging on selective attention in complex, multisource sound environments

Dinces’ basic science research focuses on understanding how the brain processes sounds into meaningful language and includes auditory scene analysis in the elderly, sound intensity processing in children, and development of auditory processing after cochlear implantation. The value of learning the role of attention and understanding the active and passive processes of stream segregation in aging populations will be to help develop therapeutic strategies to improve listening and understanding in noisy sound environments of aging adults.

Research area: fundamental auditory research

Long-term goal of research: to explain mechanisms of auditory scene analysis, which is how the auditory system processes sound into meaningful elements, that break down with aging.

Washington State University Vancouver
Neural mechanisms underlying deficits encoding temporal sound features associated with central auditory processing disorder

A critical function of the auditory system is to extract meaning from complex sounds. When this basic function is impaired, quality of life can be greatly affected. This is particularly true for speech processing, where degrading temporal information significantly alters the ability to listen. Difficulty encoding temporal cues is a hallmark central auditory processing disorder (CAPD), which is also marked by problems understanding complex sounds despite normal function of the peripheral auditory system. The origin of deficits associated with CAPD has been localized to the brain, but the neural mechanisms underlying the encoding of temporal sound cues remain poorly understood.

The goal of this research is to examine the contributions of inhibitory connections to the midbrain, the first known site in the auditory pathway that exhibits abnormal function in those with CAPD. These midbrain inputs signal temporal sound features important in the emergence of CAP and might therefore play an important role in the generation of listening problems. The results of this project will be a key step in advancing our understanding of how the processing of temporal information at the level of brain circuits relate to deficits associated with CAPD.

University of Iowa
Neural correlates of semantic structure in children who are hard of hearing

Mild to severe hearing loss places children at risk for delays in language development. One aspect of language that is affected is vocabulary development; children who are hard of hearing tend to know less about word meanings than their typical hearing peers. This gap in vocabulary skills is crucial because vocabulary is one of the strongest predictors of academic achievement. Therefore, it is essential to examine factors that are both: 1) amenable to change through intervention, and 2) influence vocabulary knowledge, in order to help close the vocabulary gap. One such factor is semantic memory structure (i.e., how the brain groups concepts with common properties). In essence, semantic structure determines how individuals understand and interact with the social and physical world. Yet, very little is known about how children with hearing loss structure semantic information in the brain. This project addresses a critical need by characterizing semantic structure in the brains of children who are hard of hearing, and results will inform vocabulary interventions. Given the predictive validity of vocabulary knowledge for academic achievement, improving vocabulary understanding in children with hearing loss has the potential to impact all aspects of language (form, content, and use).

Vanderbilt University
Biomarkers of spatial processing in auditory cortex measured with functional near-infrared spectroscopy

Central auditory processing disorders (CAPD) comprise a number of functional deficits, such as impairments in the ability to process complex information used for localizing, fusing, and discriminating acoustic objects or streams. Binaural hearing (integrating information from the two ears) represents a fundamental aspect of central auditory processing and can be objectively measured in the brain using biomarkers such as the blood oxygenation level-dependent (BOLD) signal in the auditory cortex.

Functional near-infrared spectroscopy (fNIRS) is an emerging technique for measuring the BOLD signal, and is well suited for study of CAPD clinically due to its low noise, portability, and cost effectiveness. As a clinical tool for objective measures of central auditory processing, fNIRS has a bright future. This project will measure fNIRS sensitivity to binaural tuning of BOLD responses, testing the hypothesis of broad contralateral tuning as seen with fMRI. Attention will be manipulated by tasks requiring feature detection in different modalities (location, pitch, visual). Also to be measured is the effect of task engagement on the BOLD signal, compared with passive listening, in order to yield an objective biomarker of cortical processing for task-related attention. This is an important tool when examining clinical populations (e.g. young children) who are unable to provide reliable feedback.

Auburn University
Evaluating central auditory processing (CAP), language, and cognition skills in adolescents born prematurely

This project will recruit 60 adolescents ages 12 to 15 years old with and without a premature birth history. Participants will complete a hearing evaluation, auditory processing evaluation, language evaluation, and cognition evaluation. The overall goal of the project is to determine if there are significant differences in auditory processing, language, and cognition skills among adolescents with a preterm birth history when compared with adolescents with a full-term birth history.

University of Wisconsin, Madison
Exploiting the “better ear” in bilateral cochlear implants for improved speech understanding in noisy situations

A recent study investigating selective attention abilities in cochlear implant users may point to a novel new method for improving the understanding of speech in a noisy environment. In that study, cochlear implant users showed significant improvement in speech understanding when instructed to attend to a target talker in one ear and ignore an interfering talker in the other. For some, there was a “better ear” for listening which yielded an even greater improvement. The aim of this work is to evaluate the feasibility of a novel strategy that takes advantage of these observations. A “better ear” strategy is proposed that combines (1) attending to a target talker in the “better ear” with (2) processing that separates the target talker’s speech from a noisy background, and delivers the target talker to the “better ear” and the remaining sound scene to the other ear. We believe this “better ear” strategy will be a significant step towards closing the gap in speech understanding performance between bilateral cochlear implant users and normal hearing listeners, and has the potential to provide significant improvements in speech understanding in noisy situations for patients with bilateral hearing aids, bimodal aids and other types of hearing impairments. Notably, this work is particularly important and relevant for children fitted with cochlear implants since they need to contend with noisy environments, such as classrooms, every day. The ability to hear better in these environments will lead to improved long-term social and educational development for these children.

Research area: Cochlear Implants; Central Auditory Processing Disorder

Long-term goal of research: To close the gap in speech understanding performance between cochlear implant users and normal hearing listeners. The primary outcome of this study will help determine whether the “better ear” strategy will provide a significant benefit for cochlear implant users, and whether this strategy for listening is desirable. Positive results will provide an impetus for the development of new engineering solutions surrounding the implementation of this “better ear” strategy. In addition, our proposed experimental paradigm offers a unique opportunity to study auditory attention mechanisms used in understanding speech in noisy environments. This will help further develop our understanding of the human auditory system so that we can bridge the gap in hearing-in-noise performance between hearing impaired and normal hearing listeners.

University of Pittsburgh
Signaling mechanisms of auditory cortex plasticity after noise-induced hearing loss

Exposure to loud noises is the most common cause of hearing loss, which can also lead to hyperacusis and tinnitus. Despite the high prevalence and adverse consequences of noise-induced hearing loss (NIHL), treatment options are limited to cognitive behavioral therapy and hearing prosthetics. Therefore, to aid in the development of pharmacotherapeutic or rehabilitative treatment options for impaired hearing after NIHL, it is imperative to identify the precise signaling mechanisms underlying the auditory cortex plasticity after NIHL. It is well established that reduced GABAergic signaling contributes to the plasticity of the auditory cortex after the onset of NIHL. However, the role and the timing of plasticity of the different subtypes of GABAergic inhibitory neurons remain unknown. Here, we will employ in vivo two-photon Ca2+ imaging and track the different subtypes of GABAergic inhibitory neurons after NIHL at single-cell resolution in awake mice. Determining the inhibitory circuit mechanisms underlying the plasticity of the auditory cortex after NIHL will reveal novel therapeutic targets for treating and rehabilitating impaired hearing after NIHL. Also, because auditory cortex plasticity is associated with hyperexcitability-related disorders such as tinnitus and hyperacusis, a detailed mechanistic understanding of auditory cortex plasticity will highlight a pathway toward the development of novel treatments for these disorders.

Massachusetts Eye and Ear, Harvard University
Evaluation of hearing loss and quality of life in patients with mild traumatic brain injury

This project will focus on auditory dysfunction following head injury, and findings will provide information about the pathophysiology of hearing loss after mild traumatic brain injury (TBI). To date, little has been described on this topic. We aim to assess auditory symptoms and their association with quality-of-life metrics in patients with mild TBI using patient-reported outcome measures. We further plan to analyze objective audiometric tests to understand the nature and severity of auditory dysfunction. Findings will be applied to clinical guidelines that address at-risk patients and the need for monitoring via audiometric testing. We anticipate findings will generate important discussion regarding an often-overlooked area of health effects following head injury.

Wayne State University
Cochlear electrical stimulation-induced tinnitus suppression and related neural activity change in the rat inferior colliculus

Tinnitus is a prevalent public health problem that affects millions of people and imposes a significant economic burden on society. Cochlear electrical stimulation (CES) is one promising treatment for managing tinnitus. However, little is known about the underlying mechanisms of CES-induced tinnitus suppression. In addition, electrode insertion during surgery can cause acute tissue trauma and cell losses, initiating programmed cell death within the damaged tissue of the cochlea. Recently, we demonstrated that cochlear stimulation suppressed tinnitus-like behaviors in rats, which is accompanied with tinnitus-related neural activity changes. We therefore suggest that CES-induced tinnitus suppression would be more robust when hearing is protected from implant trauma by intra-cochlear application of AM-111, a novel enzyme inhibitor.