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Abstract
Objective
This study characterised the relationship between speech intelligibility and quality in listeners with hearing loss for a range of hearing-aid processing settings and acoustic conditions.
Design
Binaural speech intelligibility scores and quality ratings were measured for sentences presented in babble noise and processed through a hearing-aid simulation. The intelligibility–quality relationship was investigated by (1) assessing the effects of experimental conditions on each task; (2) directly comparing intelligibility scores and quality ratings for each participant across the range of conditions; and (3) comparing the association between signal envelope fidelity (represented by a cepstral correlation metric) and intelligibility and quality.
Study sample
Participants were 15 adults (7 females; age range 59–81 years) with mild to moderately severe sensorineural hearing loss.
Results
Intelligibility and quality showed a positive association both with each other and with changes to signal fidelity introduced by the entire acoustic and signal-processing system including the additive noise and the hearing-aid output. As signal fidelity decreased, quality ratings changed at a slower rate than intelligibility scores. Individual psychometric functions were more variable for quality compared to intelligibility.
Conclusions
Variability in the intelligibility–quality relationship reinforces the importance of measuring both intelligibility and quality in clinical hearing-aid fittings.
Acknowledgments
The authors thank Elizabeth McNichols, Kailey Durkin and Sarah Mullervy for assistance with data collection. This work was supported by the National Institutes of Health under Grant R01 DC012289 (to P. S. and K. A.) and GN Hearing under Grant OCG6790B (to K. A. and J. K.).
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 To reduce the potential impact of intelligibility on listener ratings, the same two sentences from the IEEE corpus were used for the quality testing. Our concern was that even within a sentence-based corpus designed for speech intelligibility testing, there is variability in intelligibility from one sentence to the next (Kalikow et al. Citation1977; Nilsson et al. Citation1994; Nielsen and Dau Citation2009). This variability depends on factors including the familiarity of the keywords, the effects of context (high-predictability as opposed to low-predictability sentences), and the interaction of the sentence with the specific noise used as interference. By using the same two sentences in our experiment, the listeners could focus on differences in the acoustic quality of the signals rather than on intelligibility.