Faculty Bibliography

Cochlear implant surgery by a group of experienced surgeons proceeded without major complications. Computed tomography scans tended to underestimate cochlear obstruction, but a drill-out was infrequently required if the scan was apparently nounal

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

1. Although synaptic transmission is known to influence many aspects of neuronal development, activity rates are quite low at early ages. The present study describes a long-lasting postsynaptic response to brief periods of synaptic stimulation that may underlie such an influence. Whole-cell patch clamp recordings were made from the lateral superior olive (LSO) in a brain slice preparation from early postnatal gerbils. 2. Stimulation of the excitatory afferent pathway from the cochlear nucleus elicited a prolonged depolarization (PD) in approximately 60% of the LSO neurons tested. Low frequency stimulation (1 Hz) was as effective as tetanic stimulation in producing PDs. These synaptically evoked depolarizations ranged in amplitude from 3 to 32 mV and recovered spontaneously after 0.5-35 min. 3. The LSO neuron input resistance declined during every PD episode and remained significantly lower even after the membrane potential had recovered. These PDs were partially reversed by 2 mM Ni(+2), but 1 microM tetrodotoxin and 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were ineffective. The metabotropic glutamate receptor agonist, trans-1-aminocyclopentane-1,3-dicarboxylic acid (40 microM), produced depolarizations that outlasted the exposure period by an average of 20 min and were also partially repolarized by 2 mM Ni(+2). In contrast, the depolarizations produced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid or N-methyl-D-aspartate decayed within a much shorter period of time. 4. To test whether in vivo discharge rates are, in fact, very low during development, spontaneous activity was recorded from neurons of the auditory midbrain in gerbils before and during the onset of sound-evoked responses. The average discharge rate of auditory neurons was quite low (X = 0.4 spikes/s), although many cells displayed brief periods of rapid discharge rate (X = 37 spikes/ s). Together, these results demonstrate a novel form of developmental plasticity elicited by low rates of glutamatergic transmission that may involve a metabotropic pathway and prolonged calcium influx