Cochlear Implant Melody Recognition as a Function of Melody Frequency Range, Harmonicity, and Number of Electrodes

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Abstract
Objective: The primary goal of the present study was to determine how cochlear implant melody recognition was affected by the frequency range of the melodies, the harmonicity of these melodies, and the number of activated electrodes. The secondary goal was to investigate whether melody recognition and speech recognition were differentially affected by the limitations imposed by cochlear implant processing. Design: Four experiments were conducted. In the first experiment, 11 cochlear implant users used their clinical processors to recognize melodies of complex harmonic tones with their fundamental frequencies being in the low (104–262 Hz), middle (207–523 Hz), and high (414–1046 Hz) ranges. In the second experiment, melody recognition with pure tones was compared to melody recognition with complex harmonic tones in four subjects. In the third experiment, melody recognition was measured as a function of the number of electrodes in five subjects. In the fourth experiment, vowel and consonant recognition were measured as a function of the number of electrodes in the same five subjects who participated in the third experiment. Results: Frequency range significantly affected cochlear implant melody recognition, with higher frequency ranges producing better performance. Pure tones produced significantly better performance than complex harmonic tones. Increasing the number of activated electrodes did not affect performance with low- and middle-frequency melodies but produced better performance with high-frequency melodies. Large individual variability was observed for melody recognition, but its source seemed to be different from the source of the large variability observed in speech recognition. Conclusion: Contemporary cochlear implants do not adequately encode either temporal pitch or place pitch cues. Melody recognition and speech recognition require different signal processing strategies in future cochlear implants.