Overview of Central Auditory Processing Deficits in Older Adults

Dynamic Spatial Auditory Processing in the Elderly

Purpose

One of the most obvious functional effects of aging on the cognitive and processing processes of spatial hearing is the localization problem and the disorder of speech perception in noise. The purpose of the present study is to investigate the performance of dynamic spatial auditory processing in the elderly.

Methods

This descriptive and analytical study was conducted on 60 young participants aged from18 to 25 years old and 60 elderly participants aged from 60 to 75 old years, using speech, spatial, and qualities of hearing scale (SSQ) questionnaire, binaural masking level difference (BMLD) and dynamic quick speech in noise (DS-QSIN) tests.

Results

Comparing the average scores of the tests and the questionnaire using the independent t test showed a significant difference between the two groups (p < 0.001). It was also found that gender had no effect on the results (p > 0.05).

Conclusions

Aging is accompanied by different structural and functional changes in the auditory central nervous system, which leads to a decrease in speech perception in challenging listening environments, as well as a decrease in sound localization abilities, due to the reduction of temporal and spectral information. This problem affects the determination of the source of sound and the spatial cognition of the elderly and leads to a disturbance in the awareness of the auditory environment. Therefore, auditory rehabilitation programs can cause the improvement of spatial auditory processing performance and improve speech perception in noise in the elderly.

Hearing rehabilitation of adults with auditory processing disorder: a systematic review and meta-analysis of current evidence-based interventions

Background

For adults with auditory processing disorder (APD), listening and communicating can be difficult, potentially leading to social isolation, depression, employment difficulties and certainly reducing the quality of life. Despite existing practice guidelines suggesting treatments, the efficacy of these interventions remains uncertain due to a lack of comprehensive reviews. This systematic review and meta-analysis aim to establish current evidence on the effectiveness of interventions for APD in adults, addressing the urgent need for clarity in the field.

Methods

Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we conducted a systematic search across MEDLINE (Ovid), Embase (Ovid), Web of Science and Scopus, focusing on intervention studies involving adults with APD. Studies that met the inclusion criteria were grouped according to intervention with a meta-analysis only conducted where intervention, study design and outcome measure were comparable.

Results

Out of 1,618 screened records, 13 studies were included, covering auditory training (AT), low-gain hearing aids (LGHA), and personal remote microphone systems (PRMS). Our analysis revealed: AT, Mixed results with some improvements in speech intelligibility and listening ability, indicating potential benefits but highlighting the need for standardized protocols; LGHA, The included studies demonstrated significant improvements in monaural low redundancy speech testing (p < 0.05), suggesting LGHA could enhance speech perception in noisy environments. However, limitations include small sample sizes and potential biases in study design. PRMS, Demonstrated the most consistent evidence of benefit, significantly improving speech testing results, with no additional benefit from combining PRMS with other interventions.

Discussion

PRMS presents the most evidence-supported intervention for adults with APD, although further high-quality research is crucial for all intervention types. The establishment and implementation of standardized intervention protocols alongside rigorously validated outcome measures will enable a more evidence-based approach to managing APD in adults.

Hearing Loss and Cognitive Decline in the Aging Population: Emerging Perspectives in Audiology

In this perspective article, the author explores the connections between hearing loss, central auditory processing, and cognitive decline, offering insights into the complex dynamics at play. Drawing upon a range of studies, the relationship between age-related central auditory processing disorders and Alzheimer's disease is discussed, with the aim of enhancing our understanding of these interconnected conditions. Highlighting the evolving significance of audiologists in the dual management of cognitive health and hearing impairments, the author focuses on their role in identifying early signs of cognitive impairment and evaluates various cognitive screening tools used in this context. The discussion extends to adaptations of hearing assessments for older adults, especially those diagnosed with dementia, and highlights the significance of objective auditory electrophysiological tests. These tests are presented as vital in assessing the influence of aging and Alzheimer's disease on auditory processing capabilities and to signal cognitive dysfunction. The article underscores the critical role of audiologists in addressing the challenges faced by the aging population. The perspective calls for further research to improve diagnostic and therapeutic strategies in audiology, and emphasizes the need for a multidisciplinary approach in tackling the nexus of hearing loss, auditory processing, and cognitive decline.

Detecting Central Auditory Processing Disorders in Awake Mice

Mice are increasingly used as models of human-acquired neurological or neurodevelopmental conditions, such as autism, schizophrenia, and Alzheimer's disease. All these conditions involve central auditory processing disorders, which have been little investigated despite their potential for providing interesting insights into the mechanisms behind such disorders. Alterations of the auditory steady-state response to 40 Hz click trains are associated with an imbalance between neuronal excitation and inhibition, a mechanism thought to be common to many neurological disorders. Here, we demonstrate the value of presenting click trains at various rates to mice with chronically implanted pins above the inferior colliculus and the auditory cortex for obtaining easy, reliable, and long-lasting access to subcortical and cortical complex auditory processing in awake mice. Using this protocol on a mutant mouse model of autism with a defect of the Shank3 gene, we show that the neural response is impaired at high click rates (above 60 Hz) and that this impairment is visible subcortically-two results that cannot be obtained with classical protocols for cortical EEG recordings in response to stimulation at 40 Hz. These results demonstrate the value and necessity of a more complete investigation of central auditory processing disorders in mouse models of neurological or neurodevelopmental disorders.

Frequency detection, frequency discrimination, and spectro-temporal pattern perception in older and younger typically hearing adults

Elderly adults often experience difficulties in speech understanding, possibly due to age-related deficits in frequency perception. It is unclear whether age-related deficits in frequency perception differ between the apical or basal regions of the cochlea. It is also unclear how aging might differently affect frequency discrimination or detection of a change in frequency within a stimulus. In the present study, pure-tone frequency thresholds were measured in 19 older (61-74 years) and 20 younger (22-28 years) typically hearing adults. Participants were asked to discriminate between reference and probe frequencies or to detect changes in frequency within a probe stimulus. Broadband spectro-temporal pattern perception was also measured using the spectro-temporal modulated ripple test (SMRT). Frequency thresholds were significantly poorer in the basal than in the apical region of the cochlea; the deficit in the basal region was 2 times larger for the older than for the younger group. Frequency thresholds were significantly poorer in the older group, especially in the basal region where frequency detection thresholds were 3.9 times poorer for the older than for the younger group. SMRT thresholds were 1.5 times better for the younger than for the older group. Significant age effects were observed for SMRT thresholds and for frequency thresholds only in the basal region. SMRT thresholds were significantly correlated with frequency thresholds only in the older group. The poorer frequency and spectro-temporal pattern perception may contribute to age-related deficits in speech perception, even when audiometric thresholds are nearly normal.

Cognitive control in age-related hearing loss: A narrative review

Recent evidence suggests links between hearing loss and cognitive impairment in older adults with peripheral age-related hearing loss (ARHL). Earliest cognitive changes have been observed in cognitive control; however, a cohesive account of cognitive control alterations in older adults with peripheral ARHL is lacking. Cognitive control refers to cognitive processes that manage and regulate one's behavior to achieve desired goals. This review summarizes behavioral evidence on alterations in three cognitive control processes, including cognitive flexibility, inhibitory control, and working memory updating, in individuals with ARHL. Of the three processes, cognitive flexibility and working memory updating have been most extensively studied, with relatively fewer studies examining inhibitory control. Most consistent evidence is observed for long-term changes in cognitive flexibility, particularly in individuals with greater severity of ARHL. Equivocal evidence is seen for alterations in inhibitory control and working memory updating, with various factors contributing to inconsistencies across studies. Our review summarizes the emerging body of research on cognitive control in individuals with ARHL to guide future work in this area and considerations related to the management of cognitive issues in this population.

Stability of neural representations in the auditory midbrain across the lifespan despite age-related brainstem delays

The extent to which aging of the central auditory pathway impairs auditory perception in the elderly independent of peripheral cochlear decline is debated. To cause auditory deficits in normal hearing elderly, central aging needs to degrade neural sound representations at some point along the auditory pathway. However, inaccessible to psychophysical methods, the level of the auditory pathway at which aging starts to effectively degrade neural sound representations remains poorly differentiated. Here we tested how potential age-related changes in the auditory brainstem affect the stability of spatiotemporal multiunit complex speech-like sound representations in the auditory midbrain of old normal hearing CBA/J mice. Although brainstem conduction speed slowed down in old mice, the change was limited to the sub-millisecond range and only minimally affected temporal processing in the midbrain (i.e. gaps-in-noise sensitivity). Importantly, besides the small delay, multiunit complex temporal sound representations in the auditory midbrain did not differ between young and old mice. This shows that although small age-related neural effects in simple sound parameters in the lower brainstem may be present in aging they do not effectively deteriorate complex neural population representations at the level of the auditory midbrain when peripheral hearing remains normal. This result challenges the widespread belief of 'pure' central auditory decline as an automatic consequence of aging, at least up to the inferior colliculus. However, the stability of midbrain processing in aging emphasizes the role of undetected 'hidden' peripheral damage and accumulating effects in higher cortical auditory-cognitive processing explaining perception deficits in 'normal hearing' elderly.

Non-linguistic auditory speech processing

OBJECTIVES

A method for testing auditory processing of non-linguistic speech-like stimuli was developed and evaluated.

DESIGN

Monosyllabic words were temporally reversed and distorted. Stimuli were matched for spectrum and level. Listeners discriminated between distorted and undistorted stimuli.

STUDY SAMPLE

Three groups were tested. The Normal group was comprised of 12 normal-hearing participants. The Senior group was comprised of 12 seniors. The Hearing Loss group was comprised of 12 participants with thresholds of at least 35 dB HL at one or more frequencies.

RESULTS

The Senior group scored lower than the Normal group, and the Hearing Loss group scored lower than the Senior group. Scores for forward compressed speech were slightly higher than backward compressed speech but the difference was not statistically significant. Retest scores were slightly higher than scores on the first test, but the difference was not statistically significant.

CONCLUSIONS

Large differences in discrimination of distorted speech were observed among the three groups. Age and hearing loss separately affected performance. The depressed performance of the Senior group may be a result of "hidden hearing loss" that is attributed to cochlear synaptopathy. The backward-distorted speech task may be a useful non-linguistic test of speech processing that is language independent.

The effect of ventilation tube insertion in central auditory processing disorders in children with otitis media with effusion

INTRODUCTION

Otitis media with effusion is one of the most common diseases among children. The purpose of this research is to investigate whether the resolvement of conductive hearing loss from the insertion of a ventilation tube also improves central auditory processing disorders in children with otitis media with effusion.

METHOD

In this cross-sectional study, 20 children between 6 and 12 years old were diagnosed with otitis media with effusion and 20 normal children were included in the study. The central auditory processing status was evaluated in all patients before ventilation tube insertion and after six months by Speech Discrimination Score, Speech Reception Threshold, Words-in-Noise, Speech in Noise, Consonant Vowel in Noise tests, and the results were compared.

RESULTS

The mean score of Speech Discrimination Score and Consonant Vowel in Noise tests in the control group were significantly higher than the patient group before ventilation tube insertion and after surgery, in the patient group, the mean scores increased significantly. The mean scores of the Speech Reception Threshold, Words-in-Noise, and Speech in Noise tests in the control group were significantly lower than the patient group before ventilation tube insertion and after the operation, in the patient group, the mean scores significantly decreased. After VT insertion, these tests were close to the control group.

CONCLUSION

Restituting normal hearing by ventilation tube treatment improves central auditory abilities as shown in speech reception, speech discrimination, the ability to hear, the ability to recognize monosyllabic words, and the power of speech in the presence of noise.

Adaptive Syllable Training Improves Phoneme Identification in Older Listeners with and without Hearing Loss

Acoustic-phonetic speech training mitigates confusion between consonants and improves phoneme identification in noise. A novel training paradigm addressed two principles of perceptual learning. First, training benefits are often specific to the trained material; therefore, stimulus variability was reduced by training small sets of phonetically similar consonant-vowel-consonant syllables. Second, the training is most efficient at an optimal difficulty level; accordingly, the noise level was adapted to the participant's competency. Fifty-two adults aged between sixty and ninety years with normal hearing or moderate hearing loss participated in five training sessions within two weeks. Training sets of phonetically similar syllables contained voiced and voiceless stop and fricative consonants, as well as voiced nasals and liquids. Listeners identified consonants at the onset or the coda syllable position by matching the syllables with their orthographic equivalent within a closed set of three alternative symbols. The noise level was adjusted in a staircase procedure. Pre-post-training benefits were quantified as increased accuracy and a decrease in the required signal-to-noise ratio (SNR) and analyzed with regard to the stimulus sets and the participant's hearing abilities. The adaptive training was feasible for older adults with various degrees of hearing loss. Normal-hearing listeners performed with high accuracy at lower SNR after the training. Participants with hearing loss improved consonant accuracy but still required a high SNR. Phoneme identification improved for all stimulus sets. However, syllables within a set required noticeably different SNRs. Most significant gains occurred for voiced and voiceless stop and (af)fricative consonants. The training was beneficial for difficult consonants, but the easiest to identify consonants improved most prominently. The training enabled older listeners with different capabilities to train and improve at an individual 'edge of competence'.

Understanding the Relationship Between Age-Related Hearing Loss and Alzheimer’s Disease: A Narrative Review

Evidence suggests that hearing loss (HL), even at mild levels, increases the long-term risk of cognitive decline and incident dementia. Hearing loss is one of the modifiable risk factors for dementia, with approximately 4 million of the 50 million cases of dementia worldwide possibly attributed to untreated HL. This paper describes four possible mechanisms that have been suggested for the relationship between age-related hearing loss (ARHL) and Alzheimer’s disease (AD), which is the most common form of dementia. The first mechanism suggests mitochondrial dysfunction and altered signal pathways due to aging as a possible link between ARHL and AD. The second mechanism proposes that sensory degradation in hearing impaired people could explain the relationship between ARHL and AD. The occupation of cognitive resource (third) mechanism indicates that the association between ARHL and AD is a result of increased cognitive processing that is required to compensate for the degraded sensory input. The fourth mechanism is an expansion of the third mechanism, i.e., the function and structure interaction involves both cognitive resource occupation (neural activity) and AD pathology as the link between ARHL and AD. Exploring the specific mechanisms that provide the link between ARHL and AD has the potential to lead to innovative ideas for the diagnosis, prevention, and/or treatment of AD. This paper also provides insight into the current evidence for the use of hearing treatments as a possible treatment/prevention for AD, and if auditory assessments could provide an avenue for early detection of cognitive impairment associated with AD.

Speech Perception and Dichotic Listening Are Associated With Hearing Thresholds and Cognition, Respectively, in Unaided Presbycusis

Presbycusis or age-related hearing loss is a prevalent condition in the elderly population, which affects oral communication, especially in background noise, and has been associated with social isolation, depression, and cognitive decline. However, the mechanisms that relate hearing loss with cognition are complex and still elusive. Importantly, recent studies show that the use of hearing aids in presbycusis, which is its standard management, can induce neuroplasticity and modify performance in cognitive tests. As the majority of the previous studies on audition and cognition obtained their results from a mixed sample of subjects, including presbycusis individuals fitted and not fitted with hearing aids, here, we revisited the associations between hearing loss and cognition in a controlled sample of unaided presbycusis. We performed a cross-sectional study in 116 non-demented Chilean volunteers aged ≥65 years from the Auditory and Dementia study cohort. Specifically, we explored associations between bilateral sensorineural hearing loss, suprathreshold auditory brain stem responses, auditory processing (AP), and cognition with a comprehensive neuropsychological examination. The AP assessment included speech perception in noise (SIN), dichotic listening (dichotic digits and staggered spondaic words), and temporal processing [frequency pattern (FP) and gap-in-noise detection]. The neuropsychological evaluations included attention, memory, language, processing speed, executive function, and visuospatial abilities. We performed an exploratory factor analysis that yielded four composite factors, namely, hearing loss, auditory nerve, midbrain, and cognition. These four factors were used for generalized multiple linear regression models. We found significant models showing that hearing loss is associated with bilateral SIN performance, while dichotic listening was associated with cognition. We concluded that the comprehension of the auditory message in unaided presbycusis is a complex process that relies on audition and cognition. In unaided presbycusis with mild hearing loss (<40 dB HL), speech perception of monosyllabic words in background noise is associated with hearing levels, while cognition is associated with dichotic listening and FP.

Temporal acuity is preserved in the auditory midbrain of aged mice

Impaired temporal resolution of the central auditory system has long been suggested to contribute to speech understanding deficits in the elderly. However, it has been difficult to differentiate between direct age-related central deficits and indirect effects of confounding peripheral age-related hearing loss on temporal resolution. To differentiate this, we measured temporal acuity in the inferior colliculus (IC) of aged CBA/J and C57BL/6 mice, as a model of aging with and without concomitant hearing loss. We used two common measures of auditory temporal processing: gap detection as a measure of temporal fine structure and amplitude-modulated noise as a measure of envelope sensitivity. Importantly, auditory temporal acuity remained precise in the IC of old CBA/J mice when no or only minimal age-related hearing loss was present. In contrast, temporal acuity was only indirectly reduced by the presence of age-related hearing loss in aged C57BL/6 mice, not by affecting the brainstem precision, but by affecting the signal-to-noise ratio of the neuronal activity in the IC. This demonstrates that indirect effects of age-related peripheral hearing loss likely remain an important factor for temporal processing in aging in comparison to 'pure' central auditory decline itself. It also draws attention to the issue that the threshold difference between 'nearly normal' or 'clinically normal' hearing aging subjects in comparison to normal hearing young subjects still can have indirect effects on central auditory neural representations of temporal processing.

Investigating the Role of Auditory Processing Abilities in Long-Term Self-Reported Hearing Aid Outcomes among Adults Age 60+ Years

BACKGROUND

Self-reported hearing aid outcomes among older adults are variable and important to improve. The extent of the role of auditory processing in long-term hearing aid outcomes is not well understood.

PURPOSE

To determine how auditory processing abilities are related to self-reported hearing aid satisfaction and benefit along with either aided audibility alone or exploratory factors suggested by previous literature.

RESEARCH DESIGN

Descriptive analyses and multiple regression analyses of cross-sectional self-reported outcomes.

STUDY SAMPLE

Adult participants, >60 years (n = 78), fitted with bilateral hearing aids to treat symmetric, mild to moderate sensorineural hearing loss.

DATA COLLECTION AND ANALYSIS

Participants were recruited from a single audiology clinic to complete a series of questionnaires, behavioral assessments, and obtain data from their hearing aids, including real ear measures and data logging of hearing aid use. Multiple linear regressions were used to determine the amount of variance explained by predictive factors in self-reported hearing aid satisfaction and benefit. The primary predictive factors included gap detection threshold, spatial advantage score, dichotic difference score, and aided audibility. Exploratory factors included personality, self-efficacy, self-report of disability, and hearing aid use. All interpretations of statistical significance used p < 0.05. Effect sizes were determined using Cohen's f ² with a medium effect suggesting clinical relevance.

RESULTS

Gap detection threshold was a statistically significant predictor in both primary regression models with a medium effect size for satisfaction and a small effect size for benefit. When additional exploratory factors were included in the regression models with auditory processing abilities, gap detection and self-efficacy were both significant predictors of hearing aid satisfaction with medium effect sizes, explaining 10 and 17% of the variance, respectively. There were no medium effect sizes found for other predictor variables in either the primary or exploratory hearing aid benefit models. Additional factors were statistically significant in the models, explaining a small amount of variance, but did not meet the medium effect size criterion.

CONCLUSION

This study provides initial evidence supporting the incorporation of measures of gap detection ability and hearing aid self-efficacy into clinical practice for the interpretation of postfitting long-term hearing aid satisfaction.

Auditory Processing Disorders in Elderly Persons vs. Linguistic and Emotional Prosody

Background: Language communication, which is one of the basic forms of building and maintaining interpersonal relationships, deteriorates in elder age. One of the probable causes is a decline in auditory functioning, including auditory central processing. The aim of the present study is to evaluate the profile of central auditory processing disorders in the elderly as well as the relationship between these disorders and the perception of emotional and linguistic prosody. Methods: The Right Hemisphere Language Battery (RHLB-PL), and the Brain-Boy Universal Professional (BUP) were used. Results: There are statistically significant relationships between emotional prosody and: spatial hearing (r(18) = 0.46, p = 0.04); the time of the reaction (r(18) = 0.49, p = 0.03); recognizing the frequency pattern (r(18) = 0.49, p = 0.03 (4); and recognizing the duration pattern (r(18) = 0.45, p = 0.05. There are statistically significant correlations between linguistic prosody and: pitch discrimination (r(18) = 0.5, p = 0.02); recognition of the frequency pattern (r(18) = 0.55, p = 0.01); recognition of the temporal pattern; and emotional prosody (r(18) = 0.58, p = 0.01). Conclusions: The analysis of the disturbed components of auditory central processing among the tested samples showed a reduction in the functions related to frequency differentiation, the recognition of the temporal pattern, the process of discriminating between important sounds, and the speed of reaction. De-automation of the basic functions of auditory central processing, which we observe in older age, lowers the perception of both emotional and linguistic prosody, thus reducing the quality of communication in older people.

Cognitive Flexibility and Inhibition in Individuals with Age-Related Hearing Loss

Growing evidence suggests alterations in cognitive control processes in individuals with varying degrees of age-related hearing loss (ARHL); however, alterations in those with unaided mild ARHL are understudied. The current study examined two cognitive control processes, cognitive flexibility, and inhibition, in 21 older adults with unaided mild ARHL and 18 age- and education-matched normal hearing (NH) controls. All participants underwent comprehensive audiological and cognitive evaluations including Trail Making Test-B, Verbal Fluency, Stroop, and two Go/NoGo tasks. Group differences in cognitive flexibility and inhibition as well as associations between peripheral and central hearing ability and measures of cognitive flexibility and inhibition were investigated. Findings revealed that the ARHL group took significantly longer to complete the Stroop task and had higher error rates on NoGo trials on both Go/NoGo tasks relative to the NH controls. Additionally, poorer peripheral and central hearing were associated with poorer cognitive flexibility and inhibitory control. Our findings suggest slower and more inefficient inhibitory control in the mild ARHL group relative to the NH group and add to decades of research on the association between hearing and cognition.

Presynaptic voltage-gated calcium channels in the auditory brainstem

Sound information encoding within the initial synapses in the auditory brainstem requires reliable and precise synaptic transmission in response to rapid and large fluctuations in action potential (AP) firing rates. The magnitude and location of Ca²⁺ entry through voltage-gated Ca²⁺ channels (Ca_V) in the presynaptic terminal are key determinants in triggering AP-mediated release. In the mammalian central nervous system (CNS), the Ca_V2.1 subtype is the critical subtype for CNS function, since it is the most efficient Ca_V2 subtype in triggering AP-mediated synaptic vesicle (SV) release. Auditory brainstem synapses utilize Ca_V2.1 to sustain fast and repetitive SV release to encode sound information. Therefore, understanding the presynaptic mechanisms that control Ca_V2.1 localization, organization and biophysical properties are integral to understanding auditory processing. Here, we review our current knowledge about the control of presynaptic Ca_V2 abundance and organization in the auditory brainstem and impact on the regulation of auditory processing.

Biased auditory nerve central synaptopathy is associated with age-related hearing loss

KEY POINTS

Sound information is transmitted by different subtypes of spiral ganglion neurons (SGN) from the ear to the brain. Selective damage of SGN peripheral synapses (cochlear synaptopathy) is widely recognized as one of the primary mechanisms of hearing loss, whereas the mechanisms at the SGN central synapses remain unclear. We report that different subtypes of SGN central synapses converge at different ratios onto individual target cochlear nucleus neurons with distinct physiological properties, and show biased morphological and physiological changes during age-related hearing loss (ARHL). The results reveal a new dimension in cochlear nucleus neural circuitry that systematically reassembles and processes auditory information from different SGN subtypes, which is altered during ageing and probably contributes to the development of ARHL. In addition to known cochlear synaptopathy, the present study shows that SGN central synapses are also pathologically changed during ageing, which collectively helps us better understand the structure and function of SGNs during ARHL.

ABSTRACT

Sound information is transmitted from the cochlea to the brain by different subtypes of spiral ganglion neurons (SGN), which show varying degrees of vulnerability under pathological conditions. Selective cochlear synaptopathy, the preferential damage of certain subtypes of SGN peripheral synapses, has been recognized as one of the main mechanisms of hearing loss. The organization and function of the auditory nerve (AN) central synapses from different subtypes of SGNs remain unclear, including how different AN synapses reassemble onto individual neurons in the cochlear nucleus, as well as how they differentially change during hearing loss. Combining immunohistochemistry with electrophysiology, we investigated the convergence pattern and subtype-specific synaptopathy of AN synapses at the endbulb of Held, as well as the response properties of their postsynaptic bushy neurons in CBA/CaJ mice of either sex under normal hearing and age-related hearing loss (ARHL). We found that calretinin-expressing (type I_a ) and non-calretinin-expressing (type I_b /I_c ) endbulbs converged along a continuum of different ratios onto individual bushy neurons with varying physiological properties. Endbulbs degenerated during ageing in parallel with ARHL. Furthermore, the degeneration was more severe in non-calretinin-expressing synapses, which correlated with a gradual decrease in bushy neuron subpopulation predominantly innervated by these inputs. These synaptic and cellular changes were profound in middle-aged mice when their hearing thresholds were still relatively normal and prior to severe ARHL. Our findings suggest that biased AN central synaptopathy and the correlated shift in cochlear nucleus neuronal composition play significant roles in weakened auditory input and altered central auditory processing during ARHL.

Effects of aging on spatial hearing

BACKGROUND

Aging has several effects on auditory processing with the most important effect known as speech perception impairment in noise.

AIMS

The aim of the present study was to investigate the effects of aging on spatial hearing using quick speech in noise (QSIN) and binaural masking level difference (BMLD) tests and speech, spatial, and qualities of hearing scale (SSQ) questionnaire.

METHODS

The study was carried out on 34 elderly people, aged 60-75 years, with normal peripheral hearing and 34 young participants, aged 18-25 years. Using SSQ questionnaire and QSIN and BMLD tests, the spatial auditory processing ability was compared between the two groups.

RESULTS

Comparison of mean scores using independent t test showed that there was a significant difference in the mean scores of QSIN, BMLD tests and SSQ questionnaire between the two groups (p < 0.001). Sex was not found to have any effect on the results (p > 0.05).

DISCUSSION

Structural and neurochemical changes that occur in different parts of the central nervous system by aging affect various aspects of spatial auditory processing, such as localization, the precedence effect, and speech perception in noise.

CONCLUSIONS

Lower scores of older adults with normal hearing in SSQ questionnaire and behavioral tests, compared with younger participants, may be considered as their weak performance in spatial auditory processing. The results of the present study reconfirm the effects of aging on spatial auditory processing, such as localization and speech perception in noise.

The Characteristics of Adults with Severe Hearing Loss

BACKGROUND

Severe hearing loss impairs communication in a wide range of listening environments. However, we lack data as to the specific objective and subjective abilities of listeners with severe hearing loss. Insight into those abilities may inform treatment choices.

PURPOSE

The primary goal was to describe the audiometric profiles, spectral resolution ability, and objective and subjective speech perception of a sample of adult listeners with severe hearing loss, and to consider the relationships among those measures. We also considered the typical fitting received by individuals with severe loss, in terms of hearing aid style, electroacoustic characteristics, and features, as well as supplementary device use.

RESEARCH DESIGN

A within-subjects design was used.

STUDY SAMPLE

Participants included 36 adults aged 54-93 yr with unilateral or bilateral severe hearing loss.

DATA COLLECTION AND ANALYSIS

Testing included a full hearing and hearing aid history; audiometric evaluation; loudness growth and dynamic range; spectral resolution; assessment of cochlear dead regions; objective and subjective assessment of speech recognition; and electroacoustic evaluation of current hearing aids. Regression models were used to analyze relationships between hearing loss, spectral resolution, and speech recognition.

RESULTS

For speech in quiet, 60% of the variance was approximately equally accounted for by amount of hearing loss, spectral resolution, and number of dead regions. For speech in noise, only a modest proportion of performance variance was explained by amount of hearing loss. In general, participants were wearing amplification of appropriate style and technology for their hearing loss, but the extent of assistive technology use was low. Subjective communication ratings depended on the listening situation, but in general, were similar to previously published data for adults with mild-to-moderate loss who did not wear hearing aids.

CONCLUSIONS

The present data suggest that the range of abilities of an individual can be more fully captured with comprehensive testing. Such testing also offers an opportunity for informed counseling regarding realistic expectations for hearing aid use and the availability of hearing assistive technology.

Impact of Auditory Experience on the Structural Plasticity of the AIS in the Mouse Brainstem Throughout the Lifespan

Sound input critically influences the development and maintenance of neuronal circuits in the mammalian brain throughout life. We investigate the structural and functional plasticity of auditory neurons in response to various auditory experiences during development, adulthood, and aging. Using electrophysiology, computer simulation, and immunohistochemistry, we study the structural plasticity of the axon initial segment (AIS) in the medial nucleus of the trapezoid body (MNTB) from the auditory brainstem of the mice (either sex), in different ages and auditory environments. The structure and spatial location of the AIS of MNTB neurons depend on their functional topographic location along the tonotopic axis, aligning high- to low-frequency sound-responding neurons (HF or LF neurons). HF neurons dramatically undergo structural remodeling of the AIS throughout life. The AIS progressively shortens during development, is stabilized in adulthood, and becomes longer in aging. Sound inputs are critically associated with setting and maintaining AIS plasticity and tonotopy at various ages. Sound stimulation increases the excitability of auditory neurons. Computer simulation shows that modification of the AIS length, location, and diameter can affect firing properties of MNTB neurons in the developing brainstem. The adaptive capability of axonal structure in response to various auditory experiences at different ages suggests that sound input is important for the development and maintenance of the structural and functional properties of the auditory brain throughout life.

Clinical feasibility of auditory processing tests in Japanese older adults: a pilot study

Background: Difficulty in listening comprehension is a major audiological complaint of older adults. Behavioural auditory processing tests (APTs) may evaluate it. Aims/Objectives: The aim was to assess the feasibility of administering Japanese APTs to older adults at otolaryngology clinics. Material and Methods: Using computer programs interfaced with an audiometer, APTs (dichotic listening test; fast speech test, FST; gap detection test, GDT; speech in noise test; rapidly alternating speech perception test) were administered to 20 older adults (65-84 years old; mean 75.3 years) and 20 young adults at the 40 dB sensation level. Monosyllable speech perception (MSP) and the Mini-Mental State Examination (MMSE) were evaluated. Results: APT results except for GDT were significantly correlated with MSP. The performance on each APT was worse in older adults than in young adults (p < .01). The older adults with good MSP ≥ 80% (n = 13) or excellent cognitive function (MMSE ≥ 28; n = 11) also did worse on APTs (p < .05). A ceiling effect was noted in the APT data, with FST showing a minimum ceiling effect and reflecting interindividual variations of data. Conclusions and Significance: It is feasible to administer APTs to older adults who visit otolaryngology clinics. Among our Japanese APTs, FST may be suitable for further large-scale clinical studies.

Case studies of adults with central auditory processing disorder: Shifting the spotlight!

Vast literature exists detailing the identification and management of central auditory processing disorder in children: however, less information is available regarding central auditory processing disorder in the adult population. This study aimed to document the diagnostic and management procedure for adults presenting at a multidisciplinary clinic due to concerns regarding their listening and central auditory processing skills. This retrospective study was a case file audit of two adults (a male, aged 37 years and a female, aged 44 years) who presented at a multidisciplinary (audiology and speech pathology) clinic for a hearing and central auditory processing evaluation. Both participants completed a case history questionnaire and were then interviewed with results being documented in their file. Participants were evaluated by a dually qualified audiologist-speech pathologist on a battery of peripheral hearing tests (including pure-tone threshold audiometry, immittance measures and speech tests), central auditory processing assessments (including monaural low redundancy, dichotic listening and temporal processing tests) and evaluation of short-term auditory memory skills. Participants were self-referred, never having been assessed previously for central auditory processing disorder, yet had perceived heightened difficulty with processing information; having conversations (particularly in noisy work or social environments) and remembering information, resulting in a range of psychosocial responses. Following diagnosis of central auditory processing disorder, participants undertook an individualized short-term aural rehabilitation program as dictated by their needs and preferences. Post-program participants perceived better ability to listen and process information even in adverse listening conditions. They reported that their newly learned skills improved their work abilities and social participation leading to positive outcomes. Medical and other allied health professionals should consider the possibility of presentation of central auditory processing disorder in adulthood and make appropriate referrals for central auditory processing testing to facilitate diagnosis and appropriate intervention. Aural rehabilitation should be considered for adults newly diagnosed with central auditory processing disorder.