Effects of Interaural Latency and Frequency Mismatch on Speech Recognition for Bimodal Cochlear Implant Users

Bimodal cochlear implant (CI) users vary in speech recognition outcomes. This variability may be influenced partly by the CI and contralateral hearing aid (HA) programming procedures, which can result in mismatches in latency and frequency. We assessed the performance of bimodal listeners when latency mismatches were corrected and analyzed how frequency mismatches influenced outcomes.

Twelve adults with at least 1 year of bimodal use were evaluated in latency mismatched versus matched conditions. Masked sentence recognition was assessed in a 10-talker masker for three spatial configurations: target from the front and the masker either co-located, 90° toward the CI-ear, or 90° toward the HA-ear. Frequency mismatch for the most apical electrode (E1) was determined from postoperative imaging and the filter frequency assignment of their familiar CI map.

Participants had significantly better performance when latency mismatches were small or matched between the devices, with an approximately 10% improvement in the configuration with the masker toward the HA-ear. Significantly, poorer performance was observed with larger magnitudes of frequency mismatch, with a 2% drop in performance for every one semitone deviation increase in mismatch. The interaction between latency and frequency mismatch was nonsignificant, suggesting that the benefit of latency matching was approximately additive across the range of frequency mismatches.

Detrimental effects of interaural mismatches in latency and frequency were observed, even after long-term device use. These preliminary results suggest that bimodal CI users might benefit from individualized fitting procedures that match latency across devices and minimize frequency mismatch for the CI.

3 Laryngoscope, 135:2139-2145, 2025.