Changes in the Compressive Nonlinearity of the Cochlea During Early Aging: Estimates from Distortion OAE Input/Output Functions.

Objectives: The level-dependent growth of distortion product otoacoustic emissions (DPOAEs) provides an indirect metric of cochlear compressive nonlinearity. Recent evidence suggests that aging reduces nonlinear distortion emissions more than those associated with linear reflection. Therefore, in this study, we generate input/output (I/O) functions from the isolated distortion component of the DPOAE to probe the effects of early aging on the compressive nonlinearity of the cochlea. Design: Thirty adults whose ages ranged from 18 to 64 years participated in this study, forming a continuum of young to middle-aged subjects. When necessary for analyses, subjects were divided into a young-adult group with a mean age of 21 years, and a middle-aged group with a mean age of 52 years. All young-adult subjects and 11 of the middle-aged subjects had normal hearing; 4 middle-aged ears had slight audiometric threshold elevation at mid-to-high frequencies. DPOAEs (2f1 - f2) were recorded using primary tones swept upward in frequency from 0.5 to 8 kHz, and varied from 25 to 80 dB sound pressure level. The nonlinear distortion component of the total DPOAE was separated and used to create I/O functions at one-half octave intervals from 1.3 to 7.4 kHz. Four features of OAE compression were extracted from a fit to these functions: compression threshold, range of compression, compression slope, and low-level growth. These values were compared between age groups and correlational analyses were conducted between OAE compression threshold and age with audiometric threshold controlled. Results: Older ears had reduced DPOAE amplitude compared with young-adult ears. The OAE compression threshold was elevated at test frequencies above 2 kHz in the middle-aged subjects by 19 dB (35 versus 54 dB SPL), thereby reducing the compression range. In addition, middle-aged ears showed steeper amplitude growth beyond the compression threshold. Audiometric threshold was initially found to be a confound in establishing the relationship between compression and age; however, statistical analyses allowed us to control its variance. Correlations performed while controlling for age differences in high-frequency audiometric thresholds showed significant relationships between the DPOAE I/O compression threshold and age: Older subjects tended to have elevated compression thresholds compared with younger subjects and an extended range of monotonic growth. Conclusions: Cochlear manifestations of nonlinearity, such as the DPOAE, weaken during early aging, and DPOAE I/O functions become linearized. Commensurate changes in high-frequency audiometric thresholds are not sufficient to fully explain these changes. The results suggest that age-related changes in compressive nonlinearity could produce a reduced dynamic range of hearing, and contribute to perceptual difficulties in older listeners. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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Test-Retest Reliability of the Binaural Interaction Component of the Auditory Brainstem Response.

Objectives: The binaural interaction component (BIC) is the residual auditory brainstem response (ABR) obtained after subtracting the sum of monaurally evoked from binaurally evoked ABRs. The DN1 peak-the first negative peak of the BIC-has been postulated to have diagnostic value as a biomarker for binaural hearing abilities. Indeed, not only do DN1 amplitudes depend systematically upon binaural cues to location (interaural time and level differences), but they are also predictive of central hearing deficits in humans. A prominent issue in using BIC measures as a diagnostic biomarker is that DN1 amplitudes not only exhibit considerable variability across subjects, but also within subjects across different measurement sessions. Design: In this study, the authors investigate the DN1 amplitude measurement reliability by conducting repeated measurements on different days in eight adult guinea pigs. Results: Despite consistent ABR thresholds, ABR and DN1 amplitudes varied between and within subjects across recording sessions. However, the study analysis reveals that DN1 amplitudes varied proportionally with parent monaural ABR amplitudes, suggesting that common experimental factors likely account for the variability in both waveforms. Despite this variability, the authors show that the shape of the dependence between DN1 amplitude and interaural time difference is preserved. The authors then provide a BIC normalization strategy using monaural ABR amplitude that reduces the variability of DN1 peak measurements. Finally, the authors evaluate this normalization strategy in the context of detecting changes of the DN1 amplitude-to-interaural time difference relationship. Conclusions: The study results indicate that the BIC measurement variability can be reduced by a factor of two by performing a simple and objective normalization operation. The authors discuss the potential for this normalized BIC measure as a biomarker for binaural hearing. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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Effects of Age and Working Memory Capacity on Speech Recognition Performance in Noise Among Listeners With Normal Hearing.

Objectives: This study aimed to determine if younger and older listeners with normal hearing who differ on working memory span perform differently on speech recognition tests in noise. Older adults typically exhibit poorer speech recognition scores in noise than younger adults, which is attributed primarily to poorer hearing sensitivity and more limited working memory capacity in older than younger adults. Previous studies typically tested older listeners with poorer hearing sensitivity and shorter working memory spans than younger listeners, making it difficult to discern the importance of working memory capacity on speech recognition. This investigation controlled for hearing sensitivity and compared speech recognition performance in noise by younger and older listeners who were subdivided into high and low working memory groups. Performance patterns were compared for different speech materials to assess whether or not the effect of working memory capacity varies with the demands of the specific speech test. The authors hypothesized that (1) normal-hearing listeners with low working memory span would exhibit poorer speech recognition performance in noise than those with high working memory span; (2) older listeners with normal hearing would show poorer speech recognition scores than younger listeners with normal hearing, when the two age groups were matched for working memory span; and (3) an interaction between age and working memory would be observed for speech materials that provide contextual cues. Design: Twenty-eight older (61 to 75 years) and 25 younger (18 to 25 years) normal-hearing listeners were assigned to groups based on age and working memory status. Northwestern University Auditory Test No. 6 words and Institute of Electrical and Electronics Engineers sentences were presented in noise using an adaptive procedure to measure the signal-to-noise ratio corresponding to 50% correct performance. Cognitive ability was evaluated with two tests of working memory (Listening Span Test and Reading Span Test) and two tests of processing speed (Paced Auditory Serial Addition Test and The Letter Digit Substitution Test). Results: Significant effects of age and working memory capacity were observed on the speech recognition measures in noise, but these effects were mediated somewhat by the speech signal. Specifically, main effects of age and working memory were revealed for both words and sentences, but the interaction between the two was significant for sentences only. For these materials, effects of age were observed for listeners in the low working memory groups only. Although all cognitive measures were significantly correlated with speech recognition in noise, working memory span was the most important variable accounting for speech recognition performance. Conclusions: The results indicate that older adults with high working memory capacity are able to capitalize on contextual cues and perform as well as young listeners with high working memory capacity for sentence recognition. The data also suggest that listeners with normal hearing and low working memory capacity are less able to adapt to distortion of speech signals caused by background noise, which requires the allocation of more processing resources to earlier processing stages. These results indicate that both younger and older adults with low working memory capacity and normal hearing are at a disadvantage for recognizing speech in noise. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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How Can Public Health Approaches and Perspectives Advance Hearing Health Care?.

This commentary explores the role of public health programs and themes on hearing health care. Ongoing engagement within the hearing professional community is needed to determine how to change the landscape and identify important features in the evolution of population hearing health care. Why and how to leverage existing public health programs and develop new programs to improve hearing health in older individuals is an important topic. Hearing professionals are encouraged to reflect on these themes and recommendations and join the discussion about the future of hearing science on a population level. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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Hearing Instruments for Unilateral Severe-to-Profound Sensorineural Hearing Loss in Adults: A Systematic Review and Meta-Analysis.

Objectives: A systematic review of the literature and meta-analysis was conducted to assess the nature and quality of the evidence for the use of hearing instruments in adults with a unilateral severe to profound sensorineural hearing loss. Design: The PubMed, EMBASE, MEDLINE, Cochrane, CINAHL, and DARE databases were searched with no restrictions on language. The search included articles from the start of each database until February 11, 2015. Studies were included that (a) assessed the impact of any form of hearing instrument, including devices that reroute signals between the ears or restore aspects of hearing to a deaf ear, in adults with a sensorineural severe to profound loss in one ear and normal or near-normal hearing in the other ear; (b) compared different devices or compared a device with placebo or the unaided condition; (c) measured outcomes in terms of speech perception, spatial listening, or quality of life; (d) were prospective controlled or observational studies. Studies that met prospectively defined criteria were subjected to random effects meta-analyses. Results: Twenty-seven studies reported in 30 articles were included. The evidence was graded as low-to-moderate quality having been obtained primarily from observational before-after comparisons. The meta-analysis identified statistically significant benefits to speech perception in noise for devices that rerouted the speech signals of interest from the worse ear to the better ear using either air or bone conduction (mean benefit, 2.5 dB). However, these devices also degraded speech understanding significantly and to a similar extent (mean deficit, 3.1 dB) when noise was rerouted to the better ear. Data on the effects of cochlear implantation on speech perception could not be pooled as the prospectively defined criteria for meta-analysis were not met. Inconsistency in the assessment of outcomes relating to sound localization also precluded the synthesis of evidence across studies. Evidence for the relative efficacy of different devices was sparse but a statistically significant advantage was observed for rerouting speech signals using abutment-mounted bone conduction devices when compared with outcomes after preoperative trials of air conduction devices when speech and noise were colocated (mean benefit, 1.5 dB). Patients reported significant improvements in hearing-related quality of life with both rerouting devices and following cochlear implantation. Only two studies measured health-related quality of life and findings were inconclusive. Conclusions: Devices that reroute sounds from an ear with a severe to profound hearing loss to an ear with minimal hearing loss may improve speech perception in noise when signals of interest are located toward the impaired ear. However, the same device may also degrade speech perception as all signals are rerouted indiscriminately, including noise. Although the restoration of functional hearing in both ears through cochlear implantation could be expected to provide benefits to speech perception, the inability to synthesize evidence across existing studies means that such a conclusion cannot yet be made. For the same reason, it remains unclear whether cochlear implantation can improve the ability to localize sounds despite restoring bilateral input. Prospective controlled studies that measure outcomes consistently and control for selection and observation biases are required to improve the quality of the evidence for the provision of hearing instruments to patients with unilateral deafness and to support any future recommendations for the clinical management of these patients. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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Association Between Osteoporosis/Osteopenia and Vestibular Dysfunction in the South Korean Adults.

Objective: The associations of osteoporosis/osteopenia with vestibular dysfunction have not been well evaluated and conflicting results have been reported. The purpose of this study is to examine the relation of low bone mineral density (BMD) with vestibular dysfunction. Design: The authors conducted a cross-sectional study in 3579 Korean adults aged 50 years and older who participated in the 2009 to 2010 Korea National Health and Nutrition Examination Survey. BMD was measured by dual energy X ray absorptiometry. Vestibular dysfunction was evaluated using the modified Romberg test of standing balance on firm and compliant support surfaces. Data were analyzed in 2015. Multiple logistic regression analysis was used to compute odds ratios (ORs) and 95% confidence intervals (CIs). Results: The prevalence of vestibular dysfunction was 4.3 +/- 0.5%. After adjustment for potential confounders, the adjusted ORs for vestibular dysfunction based on BMD were 1.00 (reference) for normal BMD, 2.21 (95% CI: 1.08, 4.50) for osteopenia, and 2.47 (95% CI: 1.05, 5.81) for osteoporosis (p =65 years, the values were 1.00 (reference) for normal BMD, 2.17 (95% CI: 0.96, 4.90) for osteopenia, and 2.77 (95% CI: 1.18, 6.47) for osteoporosis (p

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Comparing the Accuracy and Speed of Manual and Tracking Methods of Measuring Hearing Thresholds.

The reliability of hearing thresholds obtained using the standard clinical method (modified Hughson-Westlake) has been the focus of previous investigation given the potential for tester bias. In recent years, more precise methods in laboratory studies have been used that control for sources of bias, often at the expense of longer test times. The aim of this pilot study was to compare test-retest variability and time requirement to obtain a full set of hearing thresholds (0.125 to 20 kHz) with the clinical, modified Hughson-Westlake (manual) method with that of the automated, modified (single frequency) Bekesy tracking method. Hearing thresholds from 10 subjects (8 females) between 19 and 47 years old (mean = 28.3; SD = 9.4) were measured using 2 methods with identical test hardware and calibration. Thresholds were obtained using the modified Hughson-Westlake (manual) method and the Bekesy method (tracking). Measurements using each method were repeated after 1 week. Test-retest variability within each measurement method was computed across test sessions. Results from each test method as well as test time across methods were compared. Test-retest variability was comparable and statistically indistinguishable between the two test methods. Thresholds were approximately 5 dB lower when measured using the tracking method. This difference was not statistically significant. The manual method of measuring thresholds was faster by approximately 4 min. Both methods required less time (~2 min) in the second session as compared with the first. Hearing thresholds obtained using the manual method can be just as reliable as those obtained using the tracking method over the large frequency range explored here (0.125 to 20 kHz). These results perhaps point to the importance of equivalent and valid calibration techniques that can overcome frequency-dependent discrepancies, most prominent at higher frequencies, in the sound pressure delivered to the ear. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

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