Musical Sound Quality in Cochlear Implant Users: A Comparison in Bass Frequency Perception Between Fine Structure Processing and High-Definition Continuous Interleaved Sampling Strategies

Objectives: Med-El cochlear implant (CI) patients are typically programmed with either the fine structure processing (FSP) or high-definition continuous interleaved sampling (HDCIS) strategy. FSP is the newer-generation strategy and aims to provide more direct encoding of fine structure information compared with HDCIS. Since fine structure information is extremely important in music listening, FSP may offer improvements in musical sound quality for CI users. Despite widespread clinical use of both strategies, few studies have assessed the possible benefits in music perception for the FSP strategy. The objective of this study is to measure the differences in musical sound quality discrimination between the FSP and HDCIS strategies. Design: Musical sound quality discrimination was measured using a previously designed evaluation, called Cochlear Implant-MUltiple Stimulus with Hidden Reference and Anchor (CI-MUSHRA). In this evaluation, participants were required to detect sound quality differences between an unaltered real-world musical stimulus and versions of the stimulus in which various amount of bass (low) frequency information was removed via a high-pass filer. Eight CI users, currently using the FSP strategy, were enrolled in this study. In the first session, participants completed the CI-MUSHRA evaluation with their FSP strategy. Patients were then programmed with the clinical-default HDCIS strategy, which they used for 2 months to allow for acclimatization. After acclimatization, each participant returned for the second session, during which they were retested with HDCIS, and then switched back to their original FSP strategy and tested acutely. Sixteen normal-hearing (NH) controls completed a CI-MUSHRA evaluation for comparison, in which NH controls listened to music samples under normal acoustic conditions, without CI stimulation. Results: Sensitivity to high-pass filtering more closely resembled that of NH controls when CI users were programmed with the clinical-default FSP strategy compared with performance when programmed with HDCIS (mixed-design analysis of variance, p < 0.05). Conclusions: The clinical-default FSP strategy offers improvements in musical sound quality discrimination for CI users with respect to bass frequency perception. This improved bass frequency discrimination may in turn support enhanced musical sound quality. This is the first study that has demonstrated objective improvements in musical sound quality discrimination with the newer-generation FSP strategy. These positive results may help guide the selection of processing strategies for Med-El CI patients. In addition, CI-MUSHRA may also provide a novel method for assessing the benefits of newer processing strategies in the future.