Understanding the Process of Integration in Binaural Cochlear Implant Configurations

Objectives: Cochlear implant (CI) users with access to hearing in both ears (binaural configurations) tend to perform better in speech perception tasks than users with a single-hearing ear alone. This benefit derives from several sources, but one central contributor may be that binaural hearing allows listeners to integrate content across ears. A substantial literature demonstrates that binaural integration differs between CI users and normal hearing controls. However, there are still questions about the underlying process of this integration. Here, we test both normal-hearing listeners and CI users to examine this process. Design: Twenty-three CI users (7 bimodal, 7 bilateral, and 9 single sided deafness CI users) and 28 age-matched normal-hearing listeners completed a dichotic listening task, in which first and second formants from one of four vowels were played to each ear in various configurations: with both formants heard diotically, with one formant heard diotically, or with one formant heard in one ear and the second formant heard in the other (dichotically). Each formant heard alone should provide minimal information for identifying the vowel. Thus, listeners must successfully integrate information from both ears if they are to show good performance in the dichotic condition. Results: Normal-hearing listeners showed no noticeable difference in performance when formants were heard diotically or dichotically. CI users showed significantly reduced performance in the dichotic condition relative to when formants were heard diotically. A deeper examination of individual participants suggests that CI users show important variation in their integration process. Conclusions: Using a dichotic listening task we provide evidence that while normal-hearing listeners successfully integrate content dichotically, CI users show remarkable differences in how they approach integration. This opens further questions regarding the circumstances in which listeners display different integration profiles and has implications for understanding variation in real-world performance outcomes.