Anatomy-based vs. logarithmic standard frequency allocation in cochlear implants: A comparative study on speech intelligibility and sound quality

Abstract

The here presented prospective, randomized, single-blinded crossover study investigated the effects of anatomy-based versus standard logarithmic frequency allocation on speech intelligibility and sound quality in 77 adult first-time cochlear implant (CI) recipients. Cochlear implant signal processing relies on filter bank configurations that distribute incoming frequencies across electrode contacts, with manufacturers typically employing standardized logarithmic frequency allocations. Recent advances in imaging technology now enable patient-specific optimization based on individual cochlear anatomy. Participants were randomly assigned to be first-fitted with either the manufacturer’s standard frequency allocation (STD) or an anatomy-based fitting (ABF). To establish ABF, postoperative cone-beam computed tomography (CBCT) scans were analyzed using Otoplan® software (Cascination, Bern, Switzerland) to determine insertion angles and intracochlear electrode positions, enabling individualized calculation of filter bank center frequencies. After three months, all participants crossed over to the alternative frequency allocation, with both configurations available for direct comparison at the second follow-up visit, and the study concluded with a final assessment at nine months. Speech intelligibility was assessed using the Freiburg monosyllabic word test in quiet and the Oldenburg sentence test in noise. Subjective hearing quality and listening preferences were evaluated through questionnaires. While statistical analyses revealed no significant differences in speech intelligibility between the two frequency allocation methods at the final visit, participants subjectively preferred the anatomy-based allocation, particularly those with single-sided deafness (SSD). These findings suggest that while speech intelligibility remains comparable between standard and individualized frequency allocations, the anatomy-based approach offers perceptual advantages in sound quality without compromising speech reception. However, further research is needed to determine whether these subjective benefits translate into measurable improvements in real-world performance and long-term satisfaction.