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Auditory processing deficits in early-onset conductive hearing loss

Principal Investigator: Merri Rosen, Ph.D.
Funding Source: National Institute for Deafness and Communication Disorders, NIH

Amount: $1,670,000

     The long-term goal of this work is to identify neural mechanisms that limit perceptual abilities as a result of developmental hearing loss. In the auditory system, chronic middle ear infections (otitis media) in children result in fluctuating conductive hearing loss (CHL) during development. The duration of hearing loss is correlated with persistent perceptual problems including speech processing deficits. Processing of time-varying auditory signals is particularly vulnerable to early hearing loss. Recent work in an animal model of conductive hearing loss shows that early hearing impairment shifts both synaptic properties and responses to sound in auditory cortex. However, it is unknown how altered synaptic elements shape cortical tuning, or how altered cortical tuning contributes to impaired perception. To address these issues, this project examines the chain of events initiated by hearing loss in order to establish the links between synaptic changes in auditory cortical neurons, their effects on the sound-evoked responses of these neurons, and impaired perception. Aim 1 will determine response properties that are vulnerable to early hearing loss. Aim 2 will determine the synaptic mechanisms that shape altered response properties of neurons in auditory cortex. Aim 3 will identify how cortical responses to auditory stimuli that are altered by hearing loss relate to perceptual impairments.

     The degree to which early hearing loss causes a simple maturational delay or novel pathology is unknown. Several neural changes due to early hearing loss indicate a delayed maturation of synaptic components and auditory responses. However, temporal response properties in hearing-impaired animals are not uniformly immature, and Aim 1 will identify those elements of time-varying stimuli that are susceptible to the effects of auditory deprivation. In particular, early hearing loss impairs processing of slow but not fast amplitude modulations (AM). However, preliminary data indicate that it may be the rate of the amplitude rise in AM signals, rather than the frequency of the modulations, that elicits abnormal neural responses. This distinction is important: speech is composed of periodic amplitude and frequency modulations with a variety of slow and fast rise times. Studies of dyslexia and specific language impairment indicate that the neural processing of a subset of these speech components is impaired, which has led to directed therapeutic interventions. This proposal will identify which stimulus parameters elicit responses that are altered by early hearing loss. Understanding the neural basis of impairments resulting from chronic conductive hearing loss is a necessary step toward providing targets for intervention and remediation.

Neural correlates of perceptual worsening: comparisons between children and juvenile animals

Principal Investigators: Merri Rosen, Ph.D.  and Julia J. Huyck, Ph.D.
Funding Source: Kent State University, NEOMED

Amount: $96,000

     Auditory perception is important for both communication and survival. It can be shaped by experience throughout the lifespan, contributing to the ability to adapt to novel stimuli and situations. While it is well established that both juveniles and adults can improve their performance on auditory perceptual tasks with training, little is known about developmental changes in the response to training. The few studies in which juveniles and adults are directly compared suggest that children are better than adults at learning certain percepts (e.g., foreign phonetic contrasts) but poorer at learning others. In fact, some adolescents have been shown to get consistently worse on an auditory task when trained using a regimen that produced learning in adults. Notably, worsening was also seen in some juvenile gerbils, but not in adults. The presence of this phenomenon in both humans and animals provides models in which we can examine both the neural and cognitive mechanisms responsible for this performance degradation. The results will improve our understanding of the mechanisms involved in auditory perceptual plasticity. Furthermore, this work may have important implications for the clinical use of perceptual training regimens for children or adolescents with hearing impairments or language problems.

Effects of developmental conductive hearing loss on communication processing: perceptual deficits and neural correlates in an animal model.

Principal Investigator: Merri Rosen, Ph.D.
Funding Source: Hearing Health Foundation

Amount: $25,000

     Conductive hearing loss (CHL), which reduces the sound conducted to the inner ear, is often associated with chronic ear infections (otitis media). There is growing awareness that CHL in children is a risk factor for speech and language deficits. However, children often have intermittent bouts of hearing loss and receive varying treatments. My research uses an animal model in which the duration and extent of CHL can be effectively controlled. This research will identify parameters of natural vocalizations (such as slow or fast changes in pitch or loudness) that are poorly detected after early CHL. Neural responses from the auditory cortex will be recorded while animals behaviorally distinguish vocalizations that vary in specific ways. This will reveal the specific vocalization components that are perceptually impaired by developmental hearing loss. These components should be used as targets for intervention and remediation. Creating training paradigms for children that target these parameters should improve speech perception and comprehension.

Neural Codes Underlying Auditory Perception in Developing Gerbils

Principal Investigator: Merri Rosen, Ph.D.
Funding Source: NEOMED Research Challenge Award

Amount: $15,000

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