Benefits of speech-based audiometry and low-gain hearing aids for blast-exposed Veterans

Va Loma Linda Healthcare System, Loma Linda CA

Investigators

Abstract

Many blast-exposed Veterans have trouble in challenging listening situations (e.g., understanding speech in background noise) despite normal or near-normal peripheral hearing as measured by the pure-tone audiogram, which we refer to as “functional hearing difficulty” (FHD). Until recently, it was unclear whether FHDs can arise from direct trauma to the central auditory system. Preliminary studies from the PI’s Career Development Award- 2 show that blast exposure: (i) damages auditory-cortical white matter tracts resulting in poorer scores on speech-in-noise tests; and (ii) produces a shift in the cortical response to speech such that background interference leads to more activation in brain regions associated with effortful listening. These findings strongly suggest a central contribution to blast related FHDs. In the past decade, VA audiologists have increasingly used low-gain hearing aids to treat FHDs, but this is problematic because conventional hearing aid fitting relies mostly on the audiogram. Thus, conventional approaches require clinical intuition to adapt the treatment to the unique needs of Veterans with FHDs. This problem also applies to sensorineural hearing loss, which has consequences beyond the peripheral structures assessed by the audiogram. This study proposes a novel data-driven approach to hearing aid fitting called speech-based audiometry (SBA). Briefly, SBA uses “Learning Machines” to structure patient-audiologist interactions toward selection of an optimal hearing-aid gain profile based on the patient’s subjective responses to aided speech. By efficiently searching a space of possible gain profiles for the optimum solution, SBA combines assessment, gain prescription, and fit refinement in a single procedure, without appealing to the audiogram. Sixty blast-exposed Veterans with FHDs will be recruited into an early-stage clinical trial and fitted for low-gain hearing aids using either the conventional approach or SBA (N = 30 per group). They will be followed for six weeks, with each group further divided into subgroups (N = 15) assigned to use their hearing aids daily or only during laboratory assessments. In Specific Aim 1, aided listening benefit will be assessed at the beginning and end of the study period using a traditional speech-in-noise instrument, the modified Quick Speech-in-Noise test. To track the effects of acclimatization to aided listening, participants will also complete a modified Digits in Noise (DIN) test once per week. Performance on the DIN will be measured traditionally (threshold signal-to-noise ratio) and in terms of “intraindividual variability,” which is inferred from response times at higher signal-to-noise ratios and reflects cognitive effort. In Specific Aim 2, participants will complete a speech-in-noise fMRI task at the beginning and end of the study period. The task will be completed with and without amplification using a simulated hearing aid to match each participant’s true gain prescription. Aided listening benefit will be characterized as reductions in activation in brain regions associated with effortful listening. For both aims, we hypothesize: (i) a significant aided listening benefit across all outcomes; (ii) a larger aided listening benefit in participants fitted with SBA vs. conventionally, potentially best captured by intraindividual variability and fMRI; and (iii) larger aided listening benefits in participants allowed to acclimatize via daily use of their hearing aids. In a second study, 112 current Veteran hearing aid users will be assessed using SBA. Specific Aim 3 will measure the difference between selected SBA gain profiles and participants’ actual prescribed gain profiles. A linear regression will be employed to determine if factors such as pure-tone thresholds, age, hearing aid experience, and history of noise or blast exposure are associated with this difference. We hypothesize that SBA will be more likely to converge with prescribed gain profiles in Veterans with higher pure-tone thresholds, more hearing aid experience, and less noise and/or blast exposure. The long- term goal of this research program is to develop SBA as an alternative hearing aid fitting approach to deliver improvements in aided listening and concrete protocols to address the needs of Veterans with deficits not adequately captured by the audiogram.