Faculty Bibliography

The purpose of this longitudinal study is to document improvements in speech intelligibility in children who have received multichannel cochlear implants, to compare their performance to that of a matched group of children with different levels of hearing loss who use conventional hearing aids. Speech intelligibility was measured by panels of listeners who analyzed recorded speech samples preimplant and at 6-month intervals following implantation. The results of this study demonstrate that prelingually deafened children with the Nucleus multichannel cochlear implant achieved significant improvements in speech intelligibility. By the 4.5- to 7.5-year intervals, the speech intelligibility exceeded 40%. $$:

English-language skills were evaluated in two groups of profoundly hearing-impaired children with the Reynell Developmental Language Scales, Revised. The first group consisted of 89 deaf children who had not received cochlear implants. The second group consisted of 23 children wearing Nucleus multichannel cochlear implants. The subjects without implants provided cross-sectional language data used to estimate the amount of language gains expected on the basis of maturation. The Reynell data from the group without implants were subjected to a regression by age. On the basis of this analysis, deaf children were predicted to make half or less of the language gains of their peers with normal hearing. Predicted language scores were then generated for the subjects with implants by using the children's preimplant Reynell Developmental Language Scale scores. The predicted scores were then compared with actual scores achieved by the subjects with implants 6 and 12 months after implantation. Twelve months after implantation, the subjects demonstrated gains in receptive and expressive language skills that exceeded by 7 months the predictions made on the basis of maturation alone. Moreover, the average language-development rate of the subjects with implants in the first year of device use was equivalent to that of children with normal hearing. These effects were observed for children with implants using both the oral and total-communication methods

Sound-pressure level (SPL) and fundamental frequency (F0) contours were obtained from four postlingually deafened adults who received cochlear implants and from a subject with Neurofibromatosis-2 (NF2) who had her hearing severely reduced following surgery to remove an auditory-nerve tumor and to implant an auditory brainstem implant. SPL and F0 contours for each phrase in passages read before and after changes in hearing were averaged over repeated readings and then normalized with respect to the highest SPL or F0 value in the contour. The regularity of each average contour was measured by calculating differences between successive syllable means and averaging the absolute values of these differences. With auditory feedback made available, the cochlear implant user with the least contour variation preimplant showed no change but all of the remaining speakers produced less variable F0 contours and three also produced less variable SPL contours. In complementary fashion, when the NF2 speaker had her auditory feedback severely reduced, she produced more variable F0 and SPL contours. The results are interpreted as supporting a dual-process theory of the role of auditory feedback in speech production, according to which one role of self-hearing is to monitor transmission conditions, leading the speaker to make changes in speech postures aimed at maintaining intelligibility

The articulator positions of a subject with a cochlear implant were measured with an electromagnetic midsagittal articulometer (EMMA) system with and without auditory feedback available to the subject via his implant. Acoustic analysis of sibilant productions included specific measures of their spectral properties as well as the F3 formant amplitude. More general postural characteristics of the utterances, such as speech rate and sound level, were measured as well. Because of the mechanical and aerodynamic interdependence of the articulators, the postural variables must be considered before attributing speech improvement to the selective correction of a phonemic target with the use of auditory feedback. The tongue blade position was related to the shape and central tendency of the /integral of/ spectra; however, changes in the spectral contrast between /s/ and /integral of/ were not related to changes in the more general postural variables of rate and sound level. These findings suggest that the cochlear implant is providing this subject with important auditory cues that he can use to monitor his speech and maintain the phonemic contrast between /s/ and /integral of/

A theoretical framework for the segmental component of speech production is outlined and some preliminary supporting data are reviewed. According to the framework, articulatory movements are programmed to achieve sequences of goals that are defined in terms of articulatory and acoustic parameters. The goals are correlates of distinctive features. Some feature correlates are determined by quantal (non-linear) relations between articulation and sound. Goals may also be influenced by other principles, such as a compromise between sufficient perceptual contrast and economy of articulatory effort, which leads to the prediction that the goal definitions correspond to regions (as opposed to points) in acoustic and articulatory space. Thus the goals are characterized by some parameter variation, which is possible partly because listeners can understand variable speech. Before utterances are produced, goal specifications are modified by prosodic influences and reduction. The sequence of modified goal specifications is converted to smooth, appropriately-timed articulatory movements by the speech motor control system. This control and the resulting kinematics are constrained in part by the biomechanical properties of the articulators. To help keep acoustic variability within perceptually-acceptable limits, speech motor control mechanisms may include a strategy by which different parts of the vocal-tract area function are adjusted in a complementary (''motor equivalent'') manner. The strategy takes advantage of the fact that for some sounds, a similar acoustic transfer function can be achieved with somewhat different area functions. The existence of such a strategy and the idea that speech motor programming is based in part on acoustic goals are supported by data that show trading relations between lip rounding and tongue-body raising in production of the vowel /u/. $$:

Voice-onset time (VOT) was measured in plosive-initial syllables uttered by five cochlear implant users prior to and repeatedly at intervals after activation of their speech processors. In 'short-term' experiments, the elicitation set was read after the subject's processor has been off for 24 h, then turned on them off again. Four out of five implant users increased voiceless and/or voiced VOTc (VOT corrected for changes in syllable duration) from preimplant baselines to final recordings made 1-3 years later. Measured acoustic correlates of speech 'posture' (average SPL, F0, and low-frequency spectral slope) changed concurrently. Results in the short-term study were largely consistent with the long term. Significant multiple regressions relating changes in VOTc to accompanying changes in postural correlates were found in both studies. This outcome is consistent with hypotheses that predict changes in both VOTc and in postural correlates with the restoration of some hearing and that allow for linkages between the two. Some of the reliable VOTc increases obtained over the long term that were not correlated with postural changes may have been caused directly by auditory validation of articulatory/acoustic relations that underlie synergisms for phoneme production

The potential influence of auditory information in the production of /s/ and /integral of/ was explored for postlingually deafened adults with four-channel Ineraid cochlear implants. Analyses of the spectra of the sibilant sounds were compared for speech obtained prior to implant activation, after early implant use and after 6 months of use. In addition, the output of the Ineraid device (measured at each of the four electrodes) was analyzed with pre- and postactivation speech samples to explore whether the speech production changes were potentially audible to the cochlear-implant user. Results indicated that subjects who showed abnormally low or incorrect contrast between /s/ and /integral of/ preactivation, and who received significant auditory benefit from their implants were able to increase the distinctiveness of their productions of the two speech sounds