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.
Keywords: Speech intelligibility; envelope modulation; hearing loss; hearing-aid signal processing; speech quality.