Central Auditory Mechanisms Research Articles

The WAY to lead—Reflections on the contributions of Dr. William A. Yost to the Speech and Hearing Science Program at ASU

In the spring of 2007, after 30 years of Dr. Yost's leadership at the Parmly Hearing Institute at Loyola University Chicago, Dr. Sid Bacon invited him to join the Department of Speech and Hearing Science (SHS) at Arizona State University. Dr. Yost served as the department chair between 2007 and 2013. Dr. Yost brought a clear vision for how auditory research could grow to best position the department in the modern era of brain research. As department chair, he developed a strategic hiring plan to grow the scope of SHS research and expand faculty expertise in critical areas outside the traditional realm of SHS. This hiring strategy resulted in my coming to ASU. This talk will reflect on Dr. Yost's leadership of the department as well as his support for understanding central auditory mechanisms in my laboratory and the example he set for being a model scientist, a devoted teacher, and a productive scholar.

The Effect of Aging on the Electrically Evoked Compound Action Potential.

To examine the effect of aging on electrically evoked compound action potential (eCAP) growth functions and their relationship with speech recognition in noise in cochlear implant (CI) users. Aging typically leads to difficulty understanding speech in background noise. Previous research has explored cognitive and central auditory mechanisms contributing to these age-related changes. However, it is likely that the peripheral auditory system may also play a role. One challenge is separating the effects of aging on cochlear structures from the effects of aging on the auditory nerve in humans. CI users provide a unique way to address this issue, as intracochlear electrical stimulation bypasses surviving hair cells and activates the auditory nerve directly. Studies in animal models suggest that age-related loss of spiral ganglion cells could lead to shallower eCAP growth functions and/or increased eCAP thresholds and potentially negatively impact speech recognition. Ten younger and 10 older postlingually deafened, adult CI recipients participated in this study. eCAP amplitude-intensity functions were recorded from a mid-array electrode and fit using linear functions. Speech recognition in noise was assessed using the Quick Speech-in-Noise (QuickSIN) test. Older CI users had significantly shallower eCAP growth functions and higher eCAP thresholds than younger CI users. eCAP growth functions were not correlated with speech recognition in noise. Results of this study suggest that older adults may have poorer neural survival, resulting in higher eCAP thresholds and shallower eCAP growth functions. These findings expand our understanding of mechanisms underlying age-related changes in the peripheral auditory system.

Does changes in mismatch negativity after tinnitus retraining therapy using tinnitus pitch as deviant stimulus, reflect subjective improvement in tinnitus handicap?

Objective: The objective of this research was to study the ability of Mismatch Negativity response parameters to assess the habituation after Tinnitus Retraining Therapy through comparing MMN parameters before and after TRT and comparing MMN in tinnitus patients to non-tinnitus patients, and correlating MMN parameters to subjective measures of tinnitus.Methodology: This research included two groups: a tinnitus group of 30 tinnitus patients who were compared with a control group that consisted of well-matched 10 normal adult subjects. All participants were subjected to full history taking, audiological examination, and MMN test. Tinnitus patients were further assessed for tinnitus severity using the Tinnitus Handicap Inventory (THI), tinnitus analyses including pitch and loudness matching, with the PMF as the deviant stimulus for the MMN test.Results: The MMN latencies were significantly shorter and the MMN amplitudes were significantly greater in the tinnitus group before TRT than the control group. The MMN amplitude after TRT has significantly decreased and the MMN latency has significantly been prolonged in both ears after TRT compared with before TRT. The MMN amplitude improvement matched the subjective improvement measured subjectively by the THI.Conclusion: Tinnitus patients showed abnormality in central auditory processing mechanisms involved in pre-attentive change detection of tinnitus-related neuronal activity. This MMN abnormality showed improvement after habituation using TRT. So, we recommend adding the MMN test in evaluating tinnitus patients objectively before and after TRT for monitoring the treatment progress, together with the usual subjective measures for assessment of the degree of tinnitus severity.

The study of otoacoustic emissions and the suppression of otoacoustic emissions in subjects with tinnitus and normal hearing: an insight to tinnitus etiology.

Introduction Analysis of the suppression effect is a simple method to evaluate cochlear status and central auditory mechanisms and, more specifically, the medial olivocochlear system. This structure may be involved in the generation of mechanisms that cause tinnitus and in the pathophysiology of tinnitus in patients with tinnitus and normal hearing. Objective To review the literature of the etiology of tinnitus on the lights of otoacoustic emissions in patients with normal hearing. Data Synthesis Individuals with tinnitus and normal hearing have a higher prevalence of alterations in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions than normal subjects. This fact suggests that dysfunctions of the outer hair cells (OHCs) might be important in the generation of the tinnitus; however, this feature is not always present in those who have the symptoms of tinnitus. Final Comments These findings suggest that OHC dysfunction is not necessary for tinnitus development—that is, there might be mechanisms other than OHC damage in the tinnitus development. On the other hand, OHC dysfunction alone is not sufficient to cause the symptom, because a great many individuals with OHC dysfunction did not complain about tinnitus.

Neuromagnetic Indicators of Tinnitus and Tinnitus Masking in Patients with and without Hearing Loss

Tinnitus is an auditory phenomenon characterised by the perception of a sound in the absence of an external auditory stimulus. Chronic subjective tinnitus is almost certainly maintained via central mechanisms, and this is consistent with observed measures of altered spontaneous brain activity. A number of putative central auditory mechanisms for tinnitus have been proposed. The influential thalamocortical dysrhythmia model suggests that tinnitus can be attributed to the disruption of coherent oscillatory activity between thalamus and cortex following hearing loss. However, the extent to which this disruption specifically contributes to tinnitus or is simply a consequence of the hearing loss is unclear because the necessary matched controls have not been tested. Here, we rigorously test several predictions made by this model in four groups of participants (tinnitus with hearing loss, tinnitus with clinically normal hearing, no tinnitus with hearing loss and no tinnitus with clinically normal hearing). Magnetoencephalography was used to measure oscillatory brain activity within different frequency bands in a ‘resting’ state and during presentation of a masking noise. Results revealed that low-frequency activity in the delta band (1–4 Hz) was significantly higher in the ‘tinnitus with hearing loss’ group compared to the ‘no tinnitus with normal hearing’ group. A planned comparison indicated that this effect was unlikely to be driven by the hearing loss alone, but could possibly be a consequence of tinnitus and hearing loss. A further interpretative linkage to tinnitus was given by the result that the delta activity tended to reduce when tinnitus was masked. High-frequency activity in the gamma band (25–80 Hz) was not correlated with tinnitus (or hearing loss). The findings partly support the thalamocortical dysrhythmia model and suggest that slow-wave (delta band) activity may be a more reliable correlate of tinnitus than high-frequency activity.

Central Auditory Mechanisms Associated with Cochlear Implantation: An Overview of Selected Studies and Comment

Recently, the evaluation of the role of the central auditory system in the utilization of cochlear implants has received much attention. In order to fully understand the results of cochlear implantation, one must have an understanding of how the brain is influenced by electrical stimulation of the auditory nerve. This review provides an overview of the structure and function of the central auditory nervous system and the changes that occur as a result of cochlear implant use. Evidence of central auditory plasticity is discussed highlighting key imaging and evoked potential studies.

Avaliação neurofisiológica das vias auditivas e do equilíbrio na afasia de broca: apresentação de um caso ilustrativo

INTRODUÇÃO: Afasia é uma alteração neurológica decorrente de uma lesão em áreas cerebrais que são responsáveis pela linguagem. Frequentemente, a afasia ocorre como resultado de um acidente vascular cerebral, comprometendo a linguagem de expressão (afasia de Broca), a linguagem de entendimento (afasia de Wernicke) ou ambas (afasia mista). A avaliação otoneurológica corresponde a um grupo de procedimentos para avaliação sequencial do sistema auditivo e vestibular a de suas relações com o sistema nervoso central. O sistema auditivo e vestibular são de grande importância no controle dos mecanismos auditivos centrais, no processamento auditivo central, no controle do senso de movimento e no equilíbrio. OBJETIVO: Nosso objetivo foi apresentar a sequência da avaliação neurológica das vias auditivas (periféricas e centrais) e do sistema vestibular em um paciente com afasia de Broca. MÉTODOS: O paciente foi submetido a avaliação otorrinolaringológica, avaliação auditiva (audiometria tonal limiar convencional), testes de imitância acústica, pesquisa do reflexo acústico, avaliação do processamento auditivo central e do sistema vestibular. CONCLUSÃO: Nossos dados demonstram a importância da avaliação neurofisiológica das vias auditivas e do sistema vestibular em pacientes com afasia de Broca, para aprimorar o diagnóstico, tratamento e o acompanhamento evolutivo.

Some effects of aging on central auditory processing

Seniors often have more difficulty understanding speech than younger adults, particularly in noisy environments. While loss in peripheral hearing sensitivity explains many of the listening problems of elderly persons, age-related declines in general cognitive skill and central auditory processing also appear to contribute. In this article, we focus primarily on the effects of age on central auditory mechanisms. To this end, we review research examining a central locus for deficits in temporal processing and summarize behavioral and event-related potential findings from our laboratory's research on the effects of aging on dichotic listening performance. Results show that age-related deficits in interhemispheric information processing may underlie some of the listening problems among seniors. We also discuss implications for clinical audiological rehabilitative efforts in this population.

Central auditory pathologies.

This chapter considers specific deficits in auditory processing ('negative' disorders) due to neurological conditions and 'positive' disorders of central auditory processing caused by abnormal activity in central auditory mechanisms. Recent work focuses on the assessment of auditory processing in disorders that are not specifically auditory. In this case, auditory measurement may provide a 'window' into the condition.

Influence of unilateral deafness on auditory evoked magnetic field.

To investigate the effect of unilateral deafness on central auditory mechanisms, we examined patients with unilateral deafness of various durations. Auditory evoked magnetic fields (AEF) were recorded using a whole-head neuromagnetometer. In patients who had unilateral deafness for more than 3 weeks, the average N100m latency in the ipsilateral hemisphere did not differ from that in the contralateral hemisphere. In addition, in some patients with congenital or early onset deafness, the equivalent current dipole (ECD) moment was larger in the ipsilateral hemisphere than in the contralateral hemisphere. These findings suggest that unilateral deafness may cause reorganization of the central auditory pathway. They also suggest that central auditory pathway in adults has some plasticity, though not as much as in childhood.

The effect of vibrato on the recognition of masked vowels

Five experiments on the identifiability of synthetic vowels masked by wideband sounds are reported. In each experiment, identification thresholds (signal/masker ratios, in decibels) were measured for two versions of four vowels: a vibrated version, in which FO varied sinusoidally around 100 Hz; and a steady version, in which F0 was fixed at 100 Hz. The first three experiments were performed on naive subjects. Experiment 1 showed that for maskers consisting of bursts of pink noise, vibrato had no effect on thresholds. In Experiment 2, where the maskers were periodic pulse trains with an F0 randomly varied between 120 and 140 Hz from trial to trial, vibrato slightly improved thresholds when the sound pressure level of the maskers was 40 dB, but had no effect for 65-dB maskers. In Experiment 3, vibrated rather than steady pulse trains were used as maskers; when these maskers were at 40 dB, the vibrated versions of the vowels were slightly less identifiable than their steady versions; but, as in Experiment 2, vibrato had no effect when the maskers were at 65 dB. Experiment 4 showed that the unmasking effect of vibrato found in Experiment 2 disappeared in subjects trained in the identification task. Finally, Experiment 5 indicated that in trained listeners, vibrato had no influence on identification performance even when the maskers and the vowels had synchronous onsets and offsets. We conclude that vibrating a vowel masked by a wideband sound can affect its identification threshold, but only for tonal maskers and in untrained listeners. This effect of vibrato should probably be considered as a Gestalt phenomenon originating from central auditory mechanisms.

Hypersensitivity to electrical stimulation of auditory nuclei follows hearing loss in cats.

The purpose of the study was to determine if permanent, sound-induced hearing loss altered behaviorally measured thresholds for the detection of electrical stimulation applied to auditory nuclei. Electrodes were placed in cochlear nucleus and inferior colliculus in four cats. Behaviorally measured thresholds for the detection of brief trains of electrical pulses were determined before and after a 48 h exposure to a 1 kHz tone of approximately 110 dB SPL. The mean decrease in electrical stimulation threshold as a result of the sound exposure was 10.4 dB. The ongoing electrical activity (in microV, rms) recorded from the electrodes showed a mean 2.2 dB decrease after the sound exposure. In some electrodes, there was partial recovery towards pre-exposure levels for stimulation threshold and for ongoing activity, but typically, the changes persisted until the animals were terminated 30 days later. The magnitudes of the decreases in stimulation threshold and background activity proved not to be highly correlated. The permanent auditory threshold shift across all cats and all frequencies was 19 dB. This mild hearing loss produced a marked alteration in certain characteristics of the central auditory mechanisms.

Auditory nuclei in the brainstem exhibit hypersensitivity to electrical stimulation as a result of sound‐induced hearing loss

Thresholds for the detection of electrical stimulation applied to auditory brainstem nuclei were previously demonstrated to decrease by 6 to 15 dB in most cases following mechanical destruction of the cochleas. In the present work electrodes were located in cochlear nucleus and in the nucleus of inferior colliculus, and detection thresholds for electrical stimulation were measured behaviorally. A 48‐h exposure to a 1‐kHz sine wave of approximately 110 dB SPL resulted in temporary threshold shifts of 50 dB or more and permanent threshold shifts of 10 to 30 dB as evaluated using evoked potential techniques. Behaviorally measured electrical‐stimulation thresholds were obtained for each electrode for a number of sessions prior to and following noise exposure. Stimulation thresholds decreased by 2 to 17 dB (hypersensitivity) immediately following the exposure to sound and for most electrodes this hypersensitivity was maintained even after recovery from the temporary portion of the threshold shift. These results indicate that a moderate hearing loss may alter the condition of central auditory mechanisms. [Work supported by NIH Grant NS 16411.]

Electrophysiological studies of central auditory mechanisms in cetaceans

Electrophysiological studies of central auditory mechanisms in cetaceans