Faculty Bibliography

Six profoundly deaf patients were studied with mapping evoked potentials (MEP) using an acoustic signal passed through the vibrotactile prosthesis. This stimulus produced an activation of the central sulcus brain cortex. When the proSthesis was placed in the presenternal area it showed N1 P1 potentials with higher voltage and a more defined cortical dipole inversion than when the prosthesis was placed in the arm or abdomen: thus the presternal stimulation is considered an adequate place for the use of vibrotactile stimulation. The MEP were recorded in 2 patients after a period of audiological training and they showed new earlier potentials. These suggest plastic changes in the processing of an acoustic signal sent from the presternal skin by the somatosensory pathway after training and involving learning procedures.

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/

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

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/. $$:

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

Articulatory and acoustic data were used to explore the following hypothesis for the vowel /u/: The objective of articulatory movements is an acoustic goal; varying and reciprocal contributions of different articulators may help to constrain acoustic variation in achieving the goal. Previous articulatory studies of similar hypotheses, expressed entirely in articulatory terms, have been confounded by interdependencies of the variables being studied (e.g., lip and mandible displacements). One case in which this problem may be minimized is that of lip rounding and tongue-body raising (formation of a velo-palatal constriction) for the vowel /u/. Lip rounding and tongue-body raising should have similar acoustic effects for /u/, mainly to lower F2. In multiple repetitions, reciprocal contributions of lip rounding and tongue-body raising could help limit F2 variability for /u/; thus this experiment looked for complementary covariation (negative correlations) in measures of these two parameters. An electro-magnetic midsagittal articulometer (EMMA) was used to track movements of midsagittal points on the tongue body, upper and lower lips, and mandible for large numbers of repetitions of utterances containing /u/. (Interpretation of the data was aided by results from area-function-to-formant modeling.) Three of four subjects showed weak negative correlations, tentatively supporting the hypothesis; a fourth showed the opposite pattern: positive correlations of lip rounding and tongue raising. The results are discussed with respect to ideas about motor equivalence, the nature of speech motor programming, and potential improvements to the paradigm