Background: During hearing aid (HA) fitting, individuals may experience better speech discrimination at normal speech levels and worse discrimination at loud speech levels than without an HA. Therefore, we investigated factors that worsen speech discrimination when the speech sound level increases.
Methods: Speech discrimination was measured in patients aged >20 years who had average hearing thresholds <90 dB on pure-tone audiometry. An insufficient benefit was defined as speech discrimination being better at 65 dB sound pressure level (SPL) with HAs than without HAs and worse at 80 dB SPL.
Results: Of the 251 participants (296 ears), 229 and 25 had sufficient benefit and insufficient benefit, respectively. Functional gains (FGs) of sufficient benefit were approximately 1/3 gain (1/3 G) at 500 and 4000 Hz and slightly larger at 1000 and 2000 Hz. Functional gains of insufficient benefit were approximately 1/2 G at 1000 and 2000 Hz, smaller at 500 and 4000 Hz, and approximately 1/3 G at 250 Hz. Moreover, the difference between 1/2 G and FG was significantly larger in the sufficient benefit group at 250 500, and 4000 Hz than in the insufficient benefit group. Additionally, the average compression ratio at 50-80 dB SPL in the insufficient benefit group was approximately 1.1 to 1.2, slightly lower than the standard values.
Conclusion: Adjusting the compression ratio and lowering the FG to approximately 1.5 and 1/3 G, respectively, may help improve speech discrimination if it worsens with increasing sound levels during HA fitting.
Keywords: Hearing aids; prosthesis fitting; speech discrimination.