Although cochlear implants provide a degraded version of the incoming sound to the listener, cochlear implantation early in life has helped thousands of children with severe hearing loss worldwide to interact verbally with their families, caregivers, teachers, and peers. This population is of great interest from a scientific viewpoint, as their auditory systems and their brains are developing with the device in place. Relatively little is known about the development of the brain under these conditions, particularly about the interaction of the degraded input to the system with the language acquisition system, the role of the neuroplasticity of the brain in the early years of life, and the factors that determine the relationship between the perception and production of sounds. Here, we focus on cochlear-implanted children's perception and production of voice pitch inflections in speech, which convey prosodic cues (question/statement contrasts, voice emotion) and word meaning (lexical tones in languages such as Chinese). A major problem in cochlear implants is that voice pitch information is poorly transmitted through the device. Yet, prosodic cues and emotional communication are critical for children's language acquisition and social development. For children learning a tonal language, the slower pitch changes convey prosodic/emotional information, while the more rapid inflections within syllables convey meaning, suggesting an even greater need for adequate pitch perception. In our previous work with adults, we have shown that listeners with cochlear implants as well as normal hearing place greater emphasis on secondary acoustic cues such as intensity changes when the primary cue is degraded. Here, we extend our work to ask how this compensatory skill develops in school-aged normally-hearing and cochlear-implanted children, and whether the shift in emphasis is also to be found in speech production by children with cochlear implants. We hypothesize that the perceptual sensitivity of children with cochlear implants to prosodic cues and lexical tones, as well as their ability to compensate by attending to secondary cues, will be determined by factors such as their age at implantation, age at onset of profound hearing loss, residual acoustic hearing, their ability to discriminate and identify dynamic pitch changes, the length of their experience with the device, and other factors such as their socio-economic status and nonverbal intelligence. We also hypothesize that the ability of children with cochlear implants to produce adequate pitch changes in their utterances, will be influenced both by their perceptual capabilities and their auditory history. Finally, we hypothesize that Mandarin-speaking children with cochlear implants will be better able to process dynamic voice pitch information than their English-speaking counterparts. The work, which will involve collaborations with labs in the US and Taiwan, is expected to have important implications for cochlear implant technology as well as rehabilitative therapies for children with cochlear implants.
Voice pitch changes in speech convey important prosodic aspects of communication, play a critical role in language acquisition, and carry additional semantic information in tonal languages such as Mandarin. However, present-day cochlear implants (CIs) do not provide adequate information about voice pitch to the listener. The proposed work will examine how English- and Mandarin-speaking school-aged child users of CIs perceive and express such information. The work has implications for CI design and rehabilitative strategies.
