The perception and production of stress and intonation by children with cochlear implants

Users of current cochlear implants have limited access to pitch information and hence to intonation in speech. This seems likely to have an important impact on prosodic perception. This thesis examines the perception and production of the prosody of stress in children with cochlear implants. The interdependence of perceptual cues to stress (pitch, timing and loudness) in English is well documented and each of these is considered in analyses of both perception and production. The subject group comprised 17 implanted (CI) children aged 5;7 to 16;11 and using ACE or SPEAK processing strategies. The aims are to establish (i) the extent to which stress and intonation are conveyed to CI children in synthesised bisyllables (BAba vs. baBA) involving controlled changes in F0, duration and amplitude (Experiment I), and in natural speech involving compound vs. phrase stress and focus (Experiment II). (ii) when pitch cues are missing or are inaudible to the listeners, do other cues such as loudness or timing contribute to the perception of stress and intonation? (iii) whether CI subjects make appropriate use of F0, duration and amplitude to convey linguistic focus in speech production (Experiment III). Results of Experiment I showed that seven of the subjects were unable to reliably hear pitch differences of 0.84 octaves. Most of the remaining subjects required a large (approx 0.5 octave) difference to reliably hear a pitch change. Performance of the CI children was poorer than that of a normal hearing group of children presented with an acoustic cochlear implant simulation. Some of the CI children who could not discriminate F0 differences in Experiment I nevertheless scored above chance in tests involving focus in natural speech in Experiment II. Similarly, some CI subjects who were above chance in the production of appropriate F0 contours in Experiment III could not hear F0 differences of 0.84 octaves. These results suggest that CI children may not necessarily rely on F0 cues to stress, and in the absence of F0 or amplitude cues, duration may provide an alternative cue