Effects of audibility and multichannel wide dynamic range compression on consonant recognition for listeners with severe hearing loss

Objective: This study examined the effects of multichannel wide-dynamic range compression (WDRC) amplification and stimulus audibility on consonant recognition and error patterns. Design: Listeners had either severe or mild to moderate sensorineural hearing loss. Each listener was monaurally fit with a wearable hearing aid using typical clinical procedures, frequency-gain parameters, and a hybrid of clinically prescribed compression ratios for desired sensation level (Scollie et al., 2005) and NAL-NL (Dillon, 1999). Consonant-vowel nonsense syllables were presented in soundfield at multiple input levels (50, 65, 80 dB SPL). Test conditions were four-channel fast-acting WDRC amplification and a control compression limiting (CL) amplification condition. Listeners identified the stimulus heard from choices presented on an on-screen display. A between-subject repeated measures design was used to evaluate consonant recognition and consonant confusion patterns. Results: Fast-acting WDRC provided a considerable audibility advantage at 50 dB SPL, especially for listeners with severe hearing loss. Listeners with mild to moderate hearing loss received less audibility improvement from the fast-acting WDRC amplification, for conversational and high level speech, when compared with listeners with severe hearing loss. Analysis of WDRC benefit scores revealed that listeners had slightly lower scores with fast-acting WDRC amplification (relative to CL) when WDRC provided minimal improvement in audibility. The negative effect was greater for listeners with mild to moderate hearing loss compared with their counterparts with severe hearing loss. Conclusions: All listeners, but particularly the severe loss group, benefited from fast-acting WDRC amplification for low-level speech. For conversational and higher speech levels (i.e., when WDRC does not confer a significant audibility advantage), fast-acting WDRC amplification seems to slightly degrade performance. Listeners' consonant confusion patterns suggest that this negative effect may be partly due to fast-acting WDRC-induced distortions, which alter specific consonant features. In support of this view, audibility accounted for a greater percentage of the variance in listeners' performance with CL amplification compared with fast-acting WDRC amplification.