Refined anatomy-based fitting reduces interaural place mismatch and improves speech outcomes, with preliminary evidence for reduced listening effort

OBJECTIVE: This study proposes a refined approach to anatomy-based fitting (rfABF) that aims to reduce interaural place mismatch in bilateral cochlear implant (CI) users with asymmetric electrode array insertions between ears, a condition frequently associated with incomplete cochlear coverage. DESIGN: Prospective monocenter proof-of-concept study comparing rfABF with conventional clinically based fitting (CBF). ABF maps were prepared using two algorithmically derived methods: one scaling inter-electrode spectral spacing (zipped), and another transposing the ratio between clinical and tonotopic frequencies (transposed). These maps were then refined based on user feedback until a natural sound quality was achieved. Assessments consisted of speech perception in quiet and noise, sound localization, subjective sound quality ratings (HISQUI19), and listening effort assessed using pupillometry. STUDY SAMPLE: Nine experienced adult bilateral CI users with interaural asymmetry in electrode array insertion depth and/or electrode array type. RESULTS: Bilateral speech understanding improved significantly with rfABF in quiet (CBF: 77.5% ± 8.1%; rfABF: 83.1% ± 8.0%; p = 0.025) and in noise under both S0N0 (signal and noise from front) and S0Ncontra (signal from front, noise from contralateral ear) configurations. Interaural place-of-stimulation mismatch was substantially reduced from a mean of 33.8° ± 27.3° to 6.4° ± 4.2° with rfABF. Exploratory, descriptive pupillometry indicated reduced listening effort in a subset of participants, reflected by lower event-related pupil dilation (ERPD) amplitudes, particularly in cases where speech intelligibility was preserved or improved. CONCLUSIONS: rfABF shows clinical potential to improve speech understanding and facilitate access to binaural cues in bilateral CI users with asymmetric electrode array insertions, with preliminary evidence for reduced listening effort.