Adaptive Processes in Hearing.

Our auditory environment is constantly changing and evolving over time, requiring us to rapidly adapt to a complex dynamic sensory input. This adaptive ability of our auditory system can be observed at different levels, from individual cell responses to complex neural mechanisms and behavior, and is essential to achieve successful speech communication, correct orientation in our full environment, and eventually survival. These adaptive processes may differ in individuals with hearing loss, whose auditory system may cope via "readapting" itself over a longer time scale to the changes in sensory input induced by hearing impairment and the compensation provided by hearing devices. These devices themselves are now able to adapt to the listener's individual environment, attentional state, and behavior. These topics related to auditory adaptation, in the broad sense of the term, were central to the 6th International Symposium on Auditory and Audiological Research held in Nyborg, Denmark, in August 2017. The symposium addressed adaptive processes in hearing from different angles, together with a wide variety of other auditory and audiological topics. The papers in this special issue result from some of the contributions presented at the symposium.

Individual Hearing Loss: Characterization, Modelling, Compensation Strategies.

It is well-established that hearing loss does not only lead to a reduction of hearing sensitivity. Large individual differences are typically observed among listeners with hearing impairment in a wide range of suprathreshold auditory measures. In many cases, audiometric thresholds cannot fully account for such individual differences, which make it challenging to find adequate compensation strategies in hearing devices. How to characterize, model, and compensate for individual hearing loss were the main topics of the fifth International Symposium on Auditory and Audiological Research (ISAAR), held in Nyborg, Denmark, in August 2015. The following collection of papers results from some of the work that was presented and discussed at the symposium.

Speech perception in medico-legal assessment of hearing disabilities.

OBJECTIVE: Examination of Danish data for medico-legal compensations regarding hearing disabilities. The study purposes are: (1) to investigate whether discrimination scores (DSs) relate to patients' subjective experience of their hearing and communication ability (the latter referring to audio-visual perception), (2) to compare DSs from different discrimination tests (auditory/audio-visual perception and without/with noise), and (3) to relate different handicap measures in the scaling used for compensation purposes in Denmark. DESIGN: Data from a 15 year period (1999-2014) were collected and analysed. STUDY SAMPLE: The data set includes 466 patients, from which 50 were omitted due to suspicion of having exaggerated their hearing disabilities. RESULTS: The DSs relate well to the patients' subjective experience of their speech perception ability. By comparing DSs for different test setups it was found that adding noise entails a relatively more difficult listening condition than removing visual cues. The hearing and communication handicap degrees were found to agree, whereas the measured handicap degrees tended to be higher than the self-assessed handicap degrees. CONCLUSIONS: The DSs can be used to assess patients' hearing and communication abilities. The difference in the obtained handicap degrees emphasizes the importance of collecting self-assessed as well as measured handicap degrees.

Hearing loss in relation to sound exposure of professional symphony orchestra musicians.

OBJECTIVES: The objectives of this study were to: (1) estimate the hearing status of classical symphony orchestra musicians and (2) investigate the hypothesis that occupational sound exposure of symphony orchestra musicians leads to elevated hearing thresholds. DESIGN: The study population comprised all the musicians from five symphony orchestras. Questionnaires were filled in by 337 subjects, and 212 subjects performed an audiometric test. For a group of 182 musicians (363 ears) the results of the audiometry was analyzed in relation to the individual exposure, which was estimated on the basis of sound measurements and questionnaire data regarding the exposure time. The mean hearing threshold at the frequencies 3, 4, and 6 kHz, corrected for age and sex, was used as outcome. RESULTS: The musician ears with the highest exposure (29 of 363) had an additional threshold shift of 6.3 dB compared with the 238 ears with lowest exposure. The observed hearing loss of musicians was smaller compared with the noise-induced permanent threshold shift (NIPTS) predicted from ISO1999. A remaining confounding effect of age after ISO7029 age corrections could be observed to explain the difference in observed and predicted NIPTS. However, the observed hearing loss difference between the left and the right ear of musicians was 2.5 dB (95% confidence interval 1.5-3.6), which was similar to the NIPTS predicted from ISO1999. Most of the musicians had better hearing at 3, 4, and 6 kHz for age than expected, however, 29 ears with the highest exposure above 90.4 dBA with a mean exposure time of 41.7 years had significantly elevated hearing thresholds. Trumpet players and the left ear of first violinists had significantly elevated hearing thresholds compared with other musicians. CONCLUSION: Most of the symphony orchestra musicians had better hearing than expected but they had a work-related risk of developing additional noise-induced hearing loss. The additional NITPS of the left ear compared with the right ear was at the expected level based on the cumulated sound exposure and ISO1999, indicating that performing music may induce hearing loss to the same extent as industrial noise.

A user-operated audiometry method based on the maximum likelihood principle and the two-alternative forced-choice paradigm.

OBJECTIVE: To create a user-operated pure-tone audiometry method based on the method of maximum likelihood (MML) and the two-alternative forced-choice (2AFC) paradigm with high test-retest reliability without the need of an external operator and with minimal influence of subjects' fluctuating response criteria. User-operated audiometry was developed as an alternative to traditional audiometry for research purposes among musicians. DESIGN: Test-retest reliability of the user-operated audiometry system was evaluated and the user-operated audiometry system was compared with traditional audiometry. STUDY SAMPLE: Test-retest reliability of user-operated 2AFC audiometry was tested with 38 naïve listeners. User-operated 2AFC audiometry was compared to traditional audiometry in 41 subjects. RESULTS: The repeatability of user-operated 2AFC audiometry was comparable to traditional audiometry with standard deviation of differences from 3.9 dB to 5.2 dB in the frequency range of 250-8000 Hz. User-operated 2AFC audiometry gave thresholds 1-2 dB lower at most frequencies compared to traditional audiometry. CONCLUSIONS: User-operated 2AFC audiometry does not require specific operating skills and the repeatability is acceptable and similar to traditional audiometry. User operated 2AFC audiometry is a reliable alternative to traditional audiometry.

Experience with cochlear implants in Greenlanders with profound hearing loss living in Greenland.

OBJECTIVE: Cochlear implant (CI) treatment was introduced to the world in the 1980s and has become a routine treatment for congenital or acquired severe-to-profound hearing loss. CI treatment requires access to a highly skilled team of ear, nose and throat specialists, audiologists and speech-language pathologists for evaluation, surgery and rehabilitation. In particular, children treated with CI are in need of long-term post-operative auditory training and other follow-up support. DESIGN: The study is retrospective with updated information on present performance. RESULTS: Since 2001, a total of 11 Greenlandic patients living in Greenland have been treated with CI, 7 children and 4 adults. Of these children, 4 use oral communication only and are full-time CI-users, 2 with full-time use of CI are still in progress with use of oral communication, and 1 has not acquired oral language yet, but has started auditory and speech training. Six children attend mainstream public school while one child is in kindergarten. Of the adults, only 1 has achieved good speech perception with full-time use of CI while 3 do not use the CI. DISCUSSION: From an epidemiological point of view, approximately 1-3 children below 6 years are in need of a CI every second year in Greenland often due to sequelae from meningitis, which may cause postinfectious deafness. Screening of new-borns for hearing has been started in Greenland establishing the basis for early diagnosis of congenital hearing impairment and subsequent intervention. The logistics and lack of availability of speech therapists in Greenland hampers possibilities for optimal language and speech therapy of CI patients in Greenland. This study aims at describing the results of CI treatment in Greenlanders and the outcome of the CI operations along with the auditory and speech/language outcomes. Finally, we present a suggestion for the future CI treatment and recommendations for an increased effort in the treatment and rehabilitation of implanted patients in Greenland.

GJB2 (Connexin-26) mutations are not frequent among hearing impaired patients in east Greenland.

OBJECTIVE: Investigate genetic causes of HI among the Inuit populations in the Arctic with a high prevalence of hearing impairment (HI). DESIGN: A cross-sectional survey with population-based controls. STUDY SAMPLE: Forty-five patients, with sensorineural or mixed HI and an available blood sample for GJB2 sequencing from DNA, were selected from 166 east Greenlanders by specialist audiology examination, including pure-tone air and bone conduction audiometry from 125 Hz to 8000 Hz. Controls were 108 east- and 109 west-Greenlanders. RESULTS: Forty-five patients with HI were included, 24 males and 21 females. Median age was 35 years (range: 5-76). The c.35delG allele frequency was 3.3%. One patient, homozygous for the c.35delG GJB2 mutation, had bilateral congenital profound HI. Another with mixed HI was heterozygous for the same mutation. Three were heterozygous for the p.V27I variant and one was heterozygous for the p.V153I variant. The frequency of the c.35delG mutation in the controls varied between 0.5% in west Greenland to 2.3% in east Greenland. CONCLUSION: The c.35delG GJB2 mutation occurs in Greenland with low frequency. We conclude the main causes behind the prevalence of HI in this population are chronic otitis media, noise traumas, and/or unidentified genetic causes.

Sound exposure of symphony orchestra musicians.

BACKGROUND: Assessment of sound exposure by noise dosimetry can be challenging especially when measuring the exposure of classical orchestra musicians where sound originate from many different instruments. A new measurement method of bilateral sound exposure of classical musicians was developed and used to characterize sound exposure of the left and right ear simultaneously in two different symphony orchestras. OBJECTIVES: To measure binaural sound exposure of professional classical musicians and to identify possible exposure risk factors of specific musicians. METHODS: Sound exposure was measured with microphones mounted on the musician's ears and recorded digitally. The recorded sound was analysed and the specific sound exposure of the left and the right ear was determined for the musicians. A total of 114 measurements covering 106 h were recorded in two symphony orchestras. RESULTS: Sound exposure depends significantly on the specific instrument and the repertoire played by the exposed musician. Concerts, group rehearsals and individual practice were all significant contributors to the sound exposure. The highest L(Aeq) of 86 -98 dB was found among the brass players. High string players were exposed from 82 to 98 dBA and their left ear was exposed 4.6 dB more than the right ear. Percussionists were exposed to high sound peaks >115 dBC but less continuous sound exposure was observed in this group. Musicians were exposed up to L(Aeq8h) of 92 dB and a majority of musicians were exposed to sound levels exceeding L(Aeq8h) of 85 dB. CONCLUSIONS: Binaural recording of the individual sound exposure showed that orchestra musicians could be exposed differently to the left and right ear and that they were primarily exposed from their own instruments. Specific repertoires as well as the specific instrument determine the level of exposure.