Binaural cue characterization in cochlear implants: Impact of signal processing and interaural linked channel...

Bilateral cochlear implantation is a primary clinical intervention to re-establish access to binaural hearing in individuals with severe-to-profound hearing loss. While many binaural auditory functions depend critically on interaural cues, existing sound coding strategies do not fully preserve these cues. Based on simulations, this study systematically examines how cochlear implant signal processing affects the encoding of interaural time and level differences across key processing stages. The impact of linked channel selection and number of maxima is also investigated on binaural cue encoding and speech intelligibility in noise. Non-linear compressions emerge as the dominant source of interaural level distortion, introducing errors up to 10.4 ± 0.5 dB. While envelope extraction and channel selection are the primary contributors to interaural timing degradation, with errors up to 101 ± 17 µs. Linking channel selection between left and right processors reduces level distortions under strong head-shadow conditions (from 1.8 ± 0.2 dB to 0.2 ± 0.1 dB), however, this improvement does not persist at later processing stages and also introduces substantial timing distortions (up to 338 ± 14 µs). Increasing maxima from 8 to 12 provides modest benefits, while further increases lead to little extra improvement, which also does not persist at later processing stages. Speech intelligibility simulation analyses show consistent benefits of linked channel selection on the side with poorer signal-to-noise ratio, also when increasing maxima from 8 to 12 to 16. These findings underscore persistent limitations in interaural cue preservation and highlight the need for coding strategies that explicitly preserve these cues.