Cochlear function tests in estimation of speech dynamic range

Abstract

Objectives: The loss of active cochlear mechanics causes elevated thresholds, loudness recruitment, and reduced frequency selectivity. The problems faced by hearing-impaired listeners are largely related with reduced dynamic range (DR). The aim of this study was to determine which index of the cochlear function tests correlates best with the DR to speech stimuli.

Methods: Audiological data on 516 ears with pure tone average (PTA) of ≤55 dB and word recognition score of ≥70% were analyzed. PTA, speech recognition threshold (SRT), uncomfortable loudness (UCL), and distortion product otoacoustic emission (DPOAE) were explored as the indices of cochlear function. Audiometric configurations were classified. Correlation between each index and the DR was assessed and multiple regression analysis was done.

Results: PTA and SRT demonstrated strong negative correlations with the DR (r = -0.788 and -0.860, respectively), while DPOAE sum was moderately correlated (r = 0.587). UCLs remained quite constant for the total range of the DR. The regression equation was Y (DR) = 75.238 - 0.719 × SRT (R(2 )=( )0.721, p < 0.001). The other variables such as audiometric configurations and DPOAE sum were excluded from the final model.

Conclusion: SRT was the most predictive of the DR among the indices of the cochlear function tests. A reduced DR in cochlear hearing loss was the product of an elevated audiometric threshold and a relatively constant UCL level. The results enable prediction of the DR from SRT and possibly PTA using the suggested regression equation.

Keywords: Distortion product otoacoustic emission; frequency selectivity; non-linearity; outer hair cell; pure tone threshold; speech recognition threshold; uncomfortable loudness level.