Binaural Diplacusis and Its Relationship with Hearing-Threshold Asymmetry

Does Endolymphatic Hydrops Shift the Cochlear Tonotopic Map?

The cochlear tonotopic map determines where along the basilar membrane traveling waves of different frequencies peak. Endolymphatic hydrops has been hypothesized to shift the tonotopic map by altering the stiffness of the cochlear partition, especially in the apex. In this exploratory study performed in a handful of normal and hydropic ears, we report preliminary measurements of interaural differences assayed using behavioral pitch-matching supplemented by measurements of reflection otoacoustic-emission phase-gradient delays.

Altered mapping of sound frequency to cochlear place in ears with endolymphatic hydrops provide insight into the pitch anomaly of diplacusis

A fundamental property of mammalian hearing is the conversion of sound pressure into a frequency-specific place of maximum vibration along the cochlear length, thereby creating a tonotopic map. The tonotopic map makes possible systematic frequency tuning across auditory-nerve fibers, which enables the brain to use pitch to separate sounds from different environmental sources and process the speech and music that connects us to people and the world. Sometimes a tone has a different pitch in the left and right ears, a perceptual anomaly known as diplacusis. Diplacusis has been attributed to a change in the cochlear frequency-place map, but the hypothesized abnormal cochlear map has never been demonstrated. Here we assess cochlear frequency-place maps in guinea-pig ears with experimentally-induced endolymphatic hydrops, a hallmark of Ménière’s disease. Our findings are consistent with the hypothesis that diplacusis is due to an altered cochlear map. Map changes can lead to altered pitch, but the size of the pitch change is also affected by neural synchrony. Our data show that the cochlear frequency-place map is not fixed but can be altered by endolymphatic hydrops. Map changes should be considered in assessing hearing pathologies and treatments.

Does person-centred care improve outcomes for musicians fitted with hearing protectors?

Objective: To reduce the risk of hearing injury, musicians are often recommended custom-made musicians' hearing protectors (MHP). Studies report benefits of use however, many still report challenges leading to relatively low uptake and inconsistent usage. Person-centred approaches to health have been shown to improve patient outcomes, and these principles may be translatable to musicians' hearing care. The aim was to investigate if use of, and satisfaction with, MHP is influenced by the treatment delivered to musicians by audiologists.Design: Participants were randomly allocated to one of four conditions that varied in extent of person-centred care.Study sample: Forty-two musicians with an interest in purchasing MHP were recruited.Results: Satisfaction with MHP was high overall and users reported a reduction in incidence of tinnitus. Participants reported few issues related to sound quality, however insertion difficulty was the main problem reported. Only one musician self-identified the need for alterations to their MHP.Conclusions: Adoption of person-centred approaches to MHP was not found to increase likelihood of use, however, satisfaction was high across all conditions. Most often, the need for MHP alterations were clinician-identified during fitting appointments or follow-up contact, underscoring the importance of including these components when providing audiological services to musicians.

Complex tone stimulation may induce binaural diplacusis with low-tone hearing loss

To clarify the possible mechanism causing binaural diplacusis with low-tone hearing loss, two psychoacoustic experiments were performed with 20 healthy subjects, using harmonic complex tones. In the first experiment, two tones were presented unilaterally, either from the right or left side. One of the tones presented was higher in frequency in terms of the fundamental component, but lower or equal in frequency in terms of the highest component, than the other tone. The subjects were asked which tone was higher in pitch after listening to both tones. They were also asked to compare tones in which low-tone components were eliminated. In the second experiment, the subjects heard these complex tones binaurally, with low-tone components eliminated in one ear. In the first experiment, most subjects perceived pitch direction, that is, higher or lower, in a reverse way when low-tone components were eliminated from the complex tones. In the second experiment, approximately half of all subjects heard the tones at different pitches in both ears. Under certain conditions, complex tone stimulation may induce binaural diplacusis when low-tone hearing is lost in one ear.

Hearing Loss, Tinnitus, Hyperacusis, and Diplacusis in Professional Musicians: A Systematic Review

Professional musicians (PMs) are at high risk of developing hearing loss (HL) and other audiological symptoms such as tinnitus, hyperacusis, and diplacusis. The aim of this systematic review is to (A) assess the risk of developing HL and audiological symptoms in PMs and (B) evaluate if different music genres (Pop/Rock Music—PR; Classical Music—CL) expose PMs to different levels of risk of developing such conditions. Forty-one articles including 4618 PMs were included in the study. HL was found in 38.6% PMs; prevalence was significantly higher among PR (63.5%) than CL (32.8%) PMs; HL mainly affected the high frequencies in the 3000-6000 Hz range and was symmetric in 68% PR PMs and in 44.5% CL PMs. Tinnitus was the most common audiological symptom, followed by hyperacusis and diplacusis. Tinnitus was almost equally distributed between PR and CL PMs; diplacusis was more common in CL than in PR PMs, while prevalence of hyperacusis was higher among PR PMs. Our review showed that PR musicians have a higher risk of developing HL compared to CL PMs; exposure to sounds of high frequency and intensity and absence of ear protection may justify these results. Difference in HL symmetry could be explained by the type of instruments used and consequent single-sided exposure.

Estimating Nonorganic Hearing Thresholds Using Binaural Auditory Stimuli

PURPOSE

Minimum contralateral interference levels (MCILs) are used to estimate true hearing thresholds in individuals with unilateral nonorganic hearing loss. In this study, we determined MCILs and examined the correspondence of MCILs to true hearing thresholds to quantify the accuracy of this procedure.

METHOD

Sixteen adults with normal hearing participated. Subjects were asked to feign a unilateral hearing loss at 1.0, 2.0, and 4.0 kHz. MCILs were determined. Subjects also made lateralization judgments for simultaneously presented tones with varying interaural intensity differences.

RESULTS

The 90% confidence intervals, calculated for the distributions, indicate that the MCIL in 90% of cases would be expected to be very close to threshold to approximately 17-19 dB poorer than the true hearing threshold. How close the MCIL is to true threshold appears to be based on the individual's response criterion.

CONCLUSIONS

Response bias influences the MCIL and how close an MCIL is to true hearing threshold. The clinician can never know a client's response bias and therefore should use a 90% confidence interval to predict the range for the expected true threshold. On the basis of this approach, a clinician may assume that true threshold is at or as much as 19 dB better than MCIL.

Binaural pitch fusion: Comparison of normal-hearing and hearing-impaired listeners

Binaural pitch fusion is the fusion of dichotically presented tones that evoke different pitches between the ears. In normal-hearing (NH) listeners, the frequency range over which binaural pitch fusion occurs is usually <0.2 octaves. Recently, broad fusion ranges of 1-4 octaves were demonstrated in bimodal cochlear implant users. In the current study, it was hypothesized that hearing aid (HA) users would also exhibit broad fusion. Fusion ranges were measured in both NH and hearing-impaired (HI) listeners with hearing losses ranging from mild-moderate to severe-profound, and relationships of fusion range with demographic factors and with diplacusis were examined. Fusion ranges of NH and HI listeners averaged 0.17 ± 0.13 octaves and 1.7 ± 1.5 octaves, respectively. In HI listeners, fusion ranges were positively correlated with a principal component measure of the covarying factors of young age, early age of hearing loss onset, and long durations of hearing loss and HA use, but not with hearing threshold, amplification level, or diplacusis. In NH listeners, no correlations were observed with age, hearing threshold, or diplacusis. The association of broad fusion with early onset, long duration of hearing loss suggests a possible role of long-term experience with hearing loss and amplification in the development of broad fusion.