Differences in consonant confusion patterns between bimodal cochlear implant users with greater and less bimodal...

The variability in bimodal advantage among bimodal users remains a significant challenge in clinical approaches. This study compared confusion patterns in consonant recognition between bimodal users who received greater bimodal advantage (GBA) and those who received less bimodal advantage (LBA), aiming to clarify these patterns in order to identify underlying causes that can help improve speech perception for all users.

Confusion matrices were measured monaurally and binaurally in both quiet and noisy conditions. Twenty-one subjects were divided into GBA (n = 8) and LBA (n = 13) groups using K-means clustering based on percentage points of bimodal advantage. Participants represented a diverse range of hearing experiences, ensuring the study's findings would apply to many bimodal users.

By analyzing consonant confusion patterns, the study identifies distinct listening strategies that differentiate GBA and LBA groups. Spectral integration was observed on /ga/, /ma/, /fa/, /ʃa/, /va/, /za/, and /ʤa/ for the GBA group but only on /ga/ and /za/ for the LBA group. Spectral interference was observed on /na/ for the GBA group, but on /ba/, /da/, /pa/, /ta/, /ka/, /ma/, /sa/, and /ʤa/ for the LBA group. Cochlear implant (CI)-ear dominance occurred on /ba/, /da/, /pa/, /ta/, /ka/, and /sa/ for the GBA group and on /na/, /fa/, /ʃa/, and /va/ for the LBA group.

These findings suggest that individual differences in speech perception among bimodal users reflect how each individual combines input from both ears. Three distinct listening strategies emerged: spectral integration, spectral interference, and CI-ear dominance. Users with greater advantage were more successful at integrating complementary inputs across ears, while others experienced conflicting auditory inputs or mainly relied on their CI ear. These results highlight the importance of looking beyond overall speech scores and focusing on specific speech sound patterns to understand why some bimodal users benefit more than others. By identifying the roles of listening strategies in consonant perception, we can better explain individual variability and improve clinical approaches to hearing device fitting.