A Sound Therapy-Based Intervention to Expand the Auditory Dynamic Range for Loudness among Persons with Sensorineural Hearing Losses: A Randomized Placebo-Controlled Clinical Trial

Abstract

The primary aim of this research was to evaluate the validity, efficacy, and generalization of principles underlying a sound therapy-based treatment for promoting expansion of the auditory dynamic range (DR) for loudness. The basic sound therapy principles, originally devised for treatment of hyperacusis among patients with tinnitus, were evaluated in this study in a target sample of unsuccessfully fit and/or problematic prospective hearing aid users with diminished DRs (owing to their elevated audiometric thresholds and reduced sound tolerance). Secondary aims included: (1) delineation of the treatment contributions from the counseling and sound therapy components to the full-treatment protocol and, in turn, the isolated treatment effects from each of these individual components to intervention success; and (2) characterization of the respective dynamics for full, partial, and control treatments. Thirty-six participants with bilateral sensorineural hearing losses and reduced DRs, which affected their actual or perceived ability to use hearing aids, were enrolled in and completed a placebo-controlled (for sound therapy) randomized clinical trial. The 2 × 2 factorial trial design was implemented with or without various assignments of counseling and sound therapy. Specifically, participants were assigned randomly to one of four treatment groups (nine participants per group), including: (1) group 1-full treatment achieved with scripted counseling plus sound therapy implemented with binaural sound generators; (2) group 2-partial treatment achieved with counseling and placebo sound generators (PSGs); (3) group 3-partial treatment achieved with binaural sound generators alone; and (4) group 4-a neutral control treatment implemented with the PSGs alone. Repeated measurements of categorical loudness judgments served as the primary outcome measure. The full-treatment categorical-loudness judgments for group 1, measured at treatment termination, were significantly greater than the corresponding pretreatment judgments measured at baseline at 500, 2,000, and 4,000 Hz. Moreover, increases in their "uncomfortably loud" judgments (∼12 dB over the range from 500 to 4,000 Hz) were superior to those measured for either of the partial-treatment groups 2 and 3 or for control group 4. Efficacy, assessed by treatment-related criterion increases ≥ 10 dB for judgments of uncomfortable loudness, was superior for full treatment (82% efficacy) compared with that for either of the partial treatments (25% and 40% for counseling combined with the placebo sound therapy and sound therapy alone, respectively) or for the control treatment (50%). The majority of the group 1 participants achieved their criterion improvements within 3 months of beginning treatment. The treatment effect from sound therapy was much greater than that for counseling, which was statistically indistinguishable in most of our analyses from the control treatment. The basic principles underlying the full-treatment protocol are valid and have general applicability for expanding the DR among individuals with sensorineural hearing losses, who may often report aided loudness problems. The positive full-treatment effects were superior to those achieved for either counseling or sound therapy in virtual or actual isolation, respectively; however, the delivery of both components in the full-treatment approach was essential for an optimum treatment outcome.

Keywords: Sound tolerance; hyperacusis; loudness discomfort level; sound therapy.

Figure 1

Baseline pure tone air-conduction thresholds and loudness discomfort levels (±1 standard error) for the left and right ears as a function of frequency for each as-treated group identified in the designated panels. Abbreviation: HL, hearing level.

Figure 2

Average real-ear frequency responses (±1 standard error) for the conventional sound generators (CSGs) and placebo sound generators (PSGs) measured for the left and right ears for groups 1 and 3 and for groups 2 and 4, respectively, at Comfortable but Slightly Soft use settings. Abbreviation: SPL, sound pressure level.

Figure 3

Average masked threshold shifts (±1 standard error) as a function of frequency for groups 1 and 3 and for groups 2 and 4, respectively, when using the conventional sound generators (CSGs) and placebo sound generators (PSGs) at their Comfortable but Slightly Soft use settings.

Figure 4

Treatment change by group for LDL (1,000 Hz) and Uncomfortably Loud categorical judgments (averaged for 500, 2,000, and 4,000 Hz) between baseline and end of treatment. Shown are the average change values (±1 standard error) for the participants in the as assigned, as treated, and dropped from analysis treatment groups. Abbreviations: CSG, conventional sound generator; LDL, loudness discomfort level; PSG, placebo sound generator.

Figure 5

Mean baseline and end-of-treatment loudness-growth functions (±1 standard error), measured for a pulsed-warbled tone are presented by group in separate panels for 500, 2,000, and 4,000 Hz. The end-of-treatment functions were constructed by averaging the resulting judgment levels for each loudness category across the last two study visits for each participant. Abbreviation: HL, hearing level.

Figure 6

Best-fitting linear-regression functions for each group highlight mean treatment dynamics for changes in Uncomfortably Loud categorical judgments (normalized relative to baseline values measured just prior to treatment onset) over time of treatment shown in months. The parameter in each group panel is measurement frequency (500, 2,000, and 4,000 Hz), identified by line type in the inset legend. Abbreviations: CSG, conventional sound generator; PSG; placebo sound generator.

Figure 7

Best-fitting (normalized to baseline) linear-regression functions characterize group 1 full-treatment dynamics for each of the seven loudness categories. Changes in the loudness judgments are shown for each category from Very Soft to Uncomfortably Loud over time of treatment in months.

Figure A1

Photographs of first-generation sound generators/placebo sound generator shells. (A) Unworn device prior to participant use. (B) Worn device at end of treatment when placebo device failure was determined by General Hearing Instruments (GHI, Harahan, LA) for the participant assigned to group 2 but moved to as-treated group 1. Note the significant erosion of the gold plating from the surface of the failed worn device, which precluded normal placebo function.

Figure A2

Photograph of second-generation sound generator shell.

Figure A3

Output decay response curve (A), frequency response curves at minimum and maximum output settings (B), and dynamic range response (C) of a typical placebo sound generator used in this study.