Deeper cochlear implant electrode insertion angle improves detection of musical sound quality deterioration related to bass frequency removal

Background: Cochlear implant (CI) electrode arrays typically do not reach the most apical regions of the cochlea that intrinsically encode low frequencies. This may contribute to diminished implant-mediated musical sound quality perception. The objective of this study was to assess the effect of varying degrees of apical cochlear stimulation (measured by angular insertion depth) on musical sound quality discrimination. Hypothesis: Increased apical cochlear stimulation will improve low-frequency perception and musical sound quality discrimination. Methods: Standard (31.5 mm, n=17) and medium (24 mm, n=8) array Med-EL CI users, and normal hearing (NH) listeners (n=16) participated. Imaging confirmed angular insertion depth. Participants completed a musical discrimination task in which they listened to a real-world musical stimulus (labeled reference) and provided sound quality ratings to versions of the reference, which included a hidden reference and test stimuli with increasing amounts of lowfrequency removal. Scores for each CI users were calculated on the basis of how much their ratings differed from NH listeners for each stimulus version. Results: Medium array and standard users had significantly different insertion depths (389.464.5 and 583.978.5 degrees, respectively; p<0.001). A significant Pearson's correlation was observed between angular insertion depth and the hidden reference scores ( p<0.05). Conclusion: CI users with greater apical stimulation made sound quality discriminations that more closely resembled those of NH controls for stimuli that contained low frequencies (<200 Hz of information). These findings suggest that increased apical cochlear stimulation improves musical low-frequency perception, which may provide a more satisfactory music listening experience for CI users.