Cochlear implant pitch and lexical tone perception in quiet and noise using F0-rate coding

Abstract

Fundamental frequency (F0) cues to voice/musical pitch can be coded by pulse-rate or amplitude modulation (AM) rate of electrical pulse-trains in cochlear implant (CI) systems. However, for most clinical strategies (e.g., ACE), temporal cues to F0 are often poorly coded, particularly for female and children's voices and/or in background noise. Strategies such as Optimized Pitch And Language (OPAL) and Fundamental Asynchronous Stimulus Timing (FAST) enhance temporal F0 cues. For OPAL, F0 is estimated and used to control the AM rate coded by electrical pulse-trains in channel containing harmonics of F0. Significant benefits of OPAL to pitch ranking, speech intonation, and Mandarin lexical tone recognition have been observed compared to ACE. For FAST, peak-timing information in channel envelopes is used to derive pulse-timing in each channel and therefore much lower stimulation rates are provided resulting in longer battery life. In bilateral CI systems, it provides better ITD sensitivity, lateralization, and spatial release from masking compared to ACE. Presented here are the results of two studies, the first explored pitch perception of harmonic tones presented in quiet and noise using experimental OPAL and FAST strategies, and the second examined Mandarin lexical tone perception in quiet and noise using ACE and OPAL in a clinical processor.