Contributions of periodicity fluctuation cues in individual frequency channels to Chinese speech recognition

Studies have revealed near perfect speech recognition with primarily temporal envelope cues and severely degraded spectral cues. Among different types of temporal envelope cues, periodicity fluctuation cues have been found to significantly improve Chinese tone and sentence recognition, while the contributions of periodicity fluctuation cues in individual frequency channels to Chinese speech recognition have not been clearly stated. In order to make periodicity fluctuation cues available in different frequency regions, the present study employed different low-pass cutoff frequencies for the temporal envelope detectors in different channels of a four-channel noise-band cochlear implant simulation. Chinese tone and vowel recognition scores were measured for six native Chinese normal hearing listeners under six low-pass cutoff frequency combinations: all 50 Hz in four channels (all-50 Hz), all 500 Hz in four channels (all-500 Hz), and 500 Hz in one of the four channels while 50 Hz in the other three channels (ch1-500 Hz, ch2-500 Hz, et al.). The results showed that the ch4-500 Hz condition produced the highest Chinese tone recognition among the four single-channel-500 Hz conditions, and was the only condition whose tone recognition was similar to that of the all-500 Hz condition and was significantly higher than that of the all-50 Hz condition. Chinese vowel recognition was not significantly affected by different cutoff frequency combinations. These results suggest that delivering periodicity fluctuation cues in higher frequency channels might be more important and efficient in enhancing Chinese tone recognition for cochlear implant patients.