Temporal and spectral analysis of melody perception with different simulated cochlear implant coding strategies

Abstract

This study examined the contribution of pitch and rhythm cues in melody recognition, as well as the quality from three well-known CI coding strategies, Advanced Combinational Encoder (ACE), Fundamental Frequency Modulation (F0mod), and Envelope Enhancement (EE). Firstly, we processed the 30 popular melodies of Taiwan children's songs using NCU-CI, a cochlear implant simulation software. In the pilot subjective listening test (n = 5), rhythm cues perceived better (p < 0.05) by having a higher percent correct and faster response time than pitch cues. Foremost, rhythm cues processed by ACE strategy achieved the best score, 86.80%. Then, objective tests were conducted to measure the spectral and temporal quality of processed melody using log spectral distance (LSD), intensity mismatch pattern, and envelope difference index (EDI). LSD between original and processed by the ACE, F0mod, and EE strategy were 2.10, 2.16, and 2.19, respectively. Then, average intensity mismatch patterns between original and processed by the ACE, F0mod, and EE strategy were 5.9, 6.4, and 6.0, respectively. The lower LSD and intensity mismatch pattern, the better the amplitude melody and spectral quality was preserved. Then, EDI between original and processed by the ACE, F0mod, and EE strategy were 0.11, 0.11, and 0.15, respectively. The higher EDI, the better the temporal envelope was preserved. It reveals that rhythm cues combined with the ACE strategy performed the best feature in CI melody perception.