Concurrent-vowel and tone recognitions in acoustic and simulated electric hearing


Because of the poor spectral resolution in cochlear implants (CIs), fundamental frequency (F0) cues are not well preserved. Chinese-speaking CI users may have great difficulty understanding speech produced by competing talkers, due to conflicting tones. In this study, normal-hearing listeners’ concurrent Chinese syllable recognition was measured with unprocessed speech and CI simulations. Concurrent syllables were constructed by summing two vowels from a male talker (with identical mean F0’s) or one vowel from each of a male and a female talker (with a relatively large F0 separation). CI signal processing was simulated using four- and eight-channel noise-band vocoders; the degraded spectral resolution may limit listeners’ ability to utilize talker and∕or tone differences. The results showed that concurrent speech recognition was significantly poorer with the CI simulations than with unprocessed speech. There were significant interactions between the talker and speech-processing conditions, e.g., better tone and syllable recognitions with the male-female condition for unprocessed speech, and with the male-male condition for eight-channel speech. With the CI simulations, competing tones interfered with concurrent-tone and syllable recognitions, but not vowel recognition. Given limited pitch cues, subjects were unable to use F0 differences between talkers or tones for concurrent Chinese syllable recognition.

Journal of the Acoustical Society of America, 125(5), 3223-3233