Impact of Vocal Effort on Respiratory and Articulatory Kinematics.

PURPOSE: The goal of this study was to examine the effects of increases in vocal effort, without changing speech intensity, on respiratory and articulatory kinematics in young adults with typical voices. METHOD: A total of 10 participants completed a reading task under three speaking conditions: baseline, mild vocal effort, and maximum vocal effort. Respiratory inductance plethysmography bands around the chest and abdomen were used to estimate lung volumes during speech, and sensor coils for electromagnetic articulography were used to transduce articulatory movements, resulting in the following outcome measures: lung volume at speech initiation (LVSI) and at speech termination (LVST), articulatory kinematic vowel space (AKVS) of two points on the tongue dorsum (body and blade), and lip aperture. RESULTS: With increases in vocal effort, and no statistical changes in speech intensity, speakers showed: (a) no statistically significant differences in LVST, (b) statistically significant increases in LVSI, (c) no statistically significant differences in AKVS measures, and (d) statistically significant reductions in lip aperture. CONCLUSIONS: Speakers with typical voices exhibited larger lung volumes at speech initiation during increases in vocal effort, paired with reduced lip displacements. To our knowledge, this is the first study to demonstrate evidence that articulatory kinematics are impacted by modulations in vocal effort. However, the mechanisms underlying vocal effort may differ between speakers with and without voice disorders. Thus, future work should examine the relationship between articulatory kinematics, respiratory kinematics, and laryngeal-level changes during vocal effort in speakers with and without voice disorders. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.17065457.

Oral configurations during vowel nasalization in English.

Speech nasalization is achieved primarily through the opening and closing of the velopharyngeal port. However, the resultant acoustic features can also be influenced by tongue configuration. Although vowel nasalization is not contrastive in English, two previous studies have found possible differences in the oral articulation of nasal and oral vowel productions, albeit with inconsistent results. In an attempt to further understand the conflicting findings, we evaluated the oral kinematics of nasalized and non-nasalized vowels in a cohort of both male and female American English speakers via electromagnetic articulography. Tongue body and lip positions were captured during vowels produced in nasal and oral contexts (e.g., /mɑm/, /bɑb/). Large contrasts were seen in all participants between tongue position of /æ/ in oral and nasal contexts, in which tongue positions were higher and more forward during /mæm/ than /bæb/. Lip aperture was smaller in a nasal context for /æ/. Lip protrusion was not different between vowels in oral and nasal contexts. Smaller contrasts in tongue and lip position were seen for vowels /ɑ, i, u/; this is consistent with biomechanical accounts of vowel production that suggest that /i, u/ are particularly constrained, whereas /æ/ has fewer biomechanical constraints, allowing for more flexibility for articulatory differences in different contexts. Thus we conclude that speakers of American English do indeed use different oral configurations for vowels that are in nasal and oral contexts, despite vowel nasalization being non-contrastive. This effect was consistent across speakers for only one vowel, perhaps accounting for previously-conflicting results.

What anticipatory coarticulation in children tells us about speech motor control maturity.

PURPOSE: This study aimed to evaluate the role of motor control immaturity in the speech production characteristics of 4-year-old children, compared to adults. Specifically, two indices were examined: trial-to-trial variability, which is assumed to be linked to motor control accuracy, and anticipatory extra-syllabic vowel-to-vowel coarticulation, which is assumed to be linked to the comprehensiveness, maturity and efficiency of sensorimotor representations in the central nervous system. METHOD: Acoustic and articulatory (ultrasound) data were recorded for 20 children and 10 adults, all native speakers of Canadian French, during the production of isolated vowels and vowel-consonant-vowel (V1-C-V2) sequences. Trial-to-trial variability was measured in isolated vowels. Extra-syllabic anticipatory coarticulation was assessed in V1-C-V2 sequences by measuring the patterns of variability of V1 associated with variations in V2. Acoustic data were reported for all subjects and articulatory data, for a subset of 6 children and 2 adults. RESULTS: Trial-to-trial variability was significantly larger in children. Systematic and significant anticipation of V2 in V1 was always found in adults, but was rare in children. Significant anticipation was observed in children only when V1 was /a/, and only along the antero-posterior dimension, with a much smaller magnitude than in adults. A closer analysis of individual speakers revealed that some children showed adult-like anticipation along this dimension, whereas the majority did not. CONCLUSION: The larger trial-to-trial variability and the lack of anticipatory behavior in most children-two phenomena that have been observed in several non-speech motor tasks-support the hypothesis that motor control immaturity may explain a large part of the differences observed between speech production in adults and 4-year-old children, apart from other causes that may be linked with language development.

Categorization in the Perception of Breathy Voice Quality and Its Relation to Voice Production in Healthy Speakers.

Purpose Previous studies of speech articulation have shown that individuals who can perceive smaller differences between similar-sounding phonemes showed larger contrasts in their productions of those phonemes. Here, a similar relationship was examined between the perception and production of breathy voice quality. Method Twenty females with healthy voices were recruited to participate in both a voice production and a perception experiment. Each participant produced repetitions of a sustained vowel, and acoustic correlates of breathiness were calculated. Identification and discrimination tasks were performed with a series of synthetic stimuli along a breathiness continuum. Categorical boundary location and boundary width were obtained from the identification task as a measurement of perception of breathiness. Spearman's correlation analysis was performed to estimate associations between values of boundary location and width and the acoustic correlates of breathiness from the participants' voices. Results Significant correlations between boundary width (r = -.53 to -.6) and some acoustic correlates were found, but no significant relationships were observed between boundary location and the acoustic correlates. Conclusions Speakers with small boundary widths, which suggest higher perceptual precision in differentiating breathiness, had typical voices that were less breathy, as estimated with acoustic measures, compared to speakers with large boundary widths. Our findings may support a link between perception and production of breathy voice quality. Supplemental Material https://doi.org/10.23641/asha.9808478.

Magnitude of Neck-Surface Vibration as an Estimate of Subglottal Pressure During Modulations of Vocal Effort and Intensity in Healthy Speakers.

Purpose: This study examined the relationship between the magnitude of neck-surface vibration (NSVMag; transduced with an accelerometer) and intraoral estimates of subglottal pressure (P'sg) during variations in vocal effort at 3 intensity levels. Method: Twelve vocally healthy adults produced strings of /pɑ/ syllables in 3 vocal intensity conditions, while increasing vocal effort during each condition. Measures were made of P'sg (estimated during stop-consonant closure), NSVMag (measured during the following vowel), sound pressure level, and respiratory kinematics. Mixed linear regression was used to analyze the relationship between NSVMag and P'sg with respect to total lung volume excursion, levels of lung volume initiation and termination, airflow, laryngeal resistance, and vocal efficiency across intensity conditions. Results: NSVMag was significantly related to P'sg (p < .001), and there was a significant, although small, interaction between NSVMag and intensity condition. Total lung excursion was the only additional variable contributing to predicting the NSVMag-P'sg relationship. Conclusions: NSVMag closely reflects P'sg during variations of vocal effort; however, the relationship changes across different intensities in some individuals. Future research should explore additional NSV-based measures (e.g., glottal airflow features) to improve estimation accuracy during voice production.

Effects of Biofeedback on Control and Generalization of Nasalization in Typical Speakers.

Purpose: The purpose of this study was to determine the effects of biofeedback on control of nasalization in individuals with typical speech. Method: Forty-eight individuals with typical speech attempted to increase and decrease vowel nasalization. During training, stimuli consisted of consonant-vowel-consonant (CVC) tokens with the center vowels /a/ or /i/ in either a nasal or nonnasal phonemic context (e.g., /mim/ vs. /bib/), depending on the participant's training group. Half of the participants had access to augmentative visual feedback during training, which was based on a less-invasive acoustic, accelerometric measure of vowel nasalization-the Horii oral-nasal coupling (HONC) score. During pre- and posttraining assessments, acoustically based nasalance was also measured from the center vowels /a/, /i/, /æ/, and /u/ of CVCs in both nasal and nonnasal contexts. Results: Linear regressions indicated that both phonemic contexts (nasal or nonnasal) and the presence of augmentative visual feedback during training were significant predictors for changes in nasalance scores from pre- to posttraining. Conclusions: Participants were able to change the nasalization of their speech following a training period with HONC biofeedback. Future work is necessary to examine the effect of such training in individuals with velopharyngeal dysfunction.

Decreased Cerebellar-Orbitofrontal Connectivity Correlates with Stuttering Severity: Whole-Brain Functional and Structural Connectivity Associations with Persistent Developmental Stuttering.

Persistent developmental stuttering is characterized by speech production disfluency and affects 1% of adults. The degree of impairment varies widely across individuals and the neural mechanisms underlying the disorder and this variability remain poorly understood. Here we elucidate compensatory mechanisms related to this variability in impairment using whole-brain functional and white matter connectivity analyses in persistent developmental stuttering. We found that people who stutter had stronger functional connectivity between cerebellum and thalamus than people with fluent speech, while stutterers with the least severe symptoms had greater functional connectivity between left cerebellum and left orbitofrontal cortex (OFC). Additionally, people who stutter had decreased functional and white matter connectivity among the perisylvian auditory, motor, and speech planning regions compared to typical speakers, but greater functional connectivity between the right basal ganglia and bilateral temporal auditory regions. Structurally, disfluency ratings were negatively correlated with white matter connections to left perisylvian regions and to the brain stem. Overall, we found increased connectivity among subcortical and reward network structures in people who stutter compared to controls. These connections were negatively correlated with stuttering severity, suggesting the involvement of cerebellum and OFC may underlie successful compensatory mechanisms by more fluent stutterers.

Diffusion imaging of cerebral white matter in persons who stutter: evidence for network-level anomalies.

Deficits in brain white matter have been a main focus of recent neuroimaging studies on stuttering. However, no prior study has examined brain connectivity on the global level of the cerebral cortex in persons who stutter (PWS). In the current study, we analyzed the results from probabilistic tractography between regions comprising the cortical speech network. An anatomical parcellation scheme was used to define 28 speech production-related ROIs in each hemisphere. We used network-based statistic (NBS) and graph theory to analyze the connectivity patterns obtained from tractography. At the network-level, the probabilistic corticocortical connectivity from the PWS group were significantly weaker than that from persons with fluent speech (PFS). NBS analysis revealed significant components in the bilateral speech networks with negative correlations with stuttering severity. To facilitate comparison with previous studies, we also performed tract-based spatial statistics (TBSS) and regional fractional anisotropy (FA) averaging. Results from tractography, TBSS and regional FA averaging jointly highlight the importance of several regions in the left peri-Rolandic sensorimotor and premotor areas, most notably the left ventral premotor cortex (vPMC) and middle primary motor cortex, in the neuroanatomical basis of stuttering.

Impaired timing adjustments in response to time-varying auditory perturbation during connected speech production in persons who stutter.

Auditory feedback (AF), the speech signal received by a speaker's own auditory system, contributes to the online control of speech movements. Recent studies based on AF perturbation provided evidence for abnormalities in the integration of auditory error with ongoing articulation and phonation in persons who stutter (PWS), but stopped short of examining connected speech. This is a crucial limitation considering the importance of sequencing and timing in stuttering. In the current study, we imposed time-varying perturbations on AF while PWS and fluent participants uttered a multisyllabic sentence. Two distinct types of perturbations were used to separately probe the control of the spatial and temporal parameters of articulation. While PWS exhibited only subtle anomalies in the AF-based spatial control, their AF-based fine-tuning of articulatory timing was substantially weaker than normal, especially in early parts of the responses, indicating slowness in the auditory-motor integration for temporal control.

Five decades of research in speech motor control: what have we learned, and where should we go from here?

PURPOSE: The author presents a view of research in speech motor control over the past 5 decades, as observed from within Ken Stevens's Speech Communication Group (SCG) in the Research Laboratory of Electronics at MIT. METHOD: The author presents a limited overview of some important developments and discoveries. The perspective is based largely on the research interests of the Speech Motor Control Group (SMCG) within the SCG; thus, it is selective, focusing on normal motor control of the vocal tract in the production of sound segments and syllables. It also covers the particular theories and models that drove the research. Following a brief introduction, there are sections on methodological advances, scientific advances, and conclusions. RESULTS: Scientific and methodological advances have been closely interrelated. Advances in instrumentation and computer hardware and software have made it possible to record and process increasingly large, multifaceted data sets; introduce new paradigms for feedback perturbation; image brain activity; and develop more sophisticated, computational physiological and neural models. Such approaches have led to increased understanding of the widespread variability in speech, motor-equivalent trading relations, sensory goals, and the nature of feedback and feedforward neural control mechanisms. CONCLUSIONS: Some ideas about important future directions for speech research are presented.

Weak responses to auditory feedback perturbation during articulation in persons who stutter: evidence for abnormal auditory-motor transformation.

Previous empirical observations have led researchers to propose that auditory feedback (the auditory perception of self-produced sounds when speaking) functions abnormally in the speech motor systems of persons who stutter (PWS). Researchers have theorized that an important neural basis of stuttering is the aberrant integration of auditory information into incipient speech motor commands. Because of the circumstantial support for these hypotheses and the differences and contradictions between them, there is a need for carefully designed experiments that directly examine auditory-motor integration during speech production in PWS. In the current study, we used real-time manipulation of auditory feedback to directly investigate whether the speech motor system of PWS utilizes auditory feedback abnormally during articulation and to characterize potential deficits of this auditory-motor integration. Twenty-one PWS and 18 fluent control participants were recruited. Using a short-latency formant-perturbation system, we examined participants' compensatory responses to unanticipated perturbation of auditory feedback of the first formant frequency during the production of the monophthong [ε]. The PWS showed compensatory responses that were qualitatively similar to the controls' and had close-to-normal latencies (∼150 ms), but the magnitudes of their responses were substantially and significantly smaller than those of the control participants (by 47% on average, p<0.05). Measurements of auditory acuity indicate that the weaker-than-normal compensatory responses in PWS were not attributable to a deficit in low-level auditory processing. These findings are consistent with the hypothesis that stuttering is associated with functional defects in the inverse models responsible for the transformation from the domain of auditory targets and auditory error information into the domain of speech motor commands.

Movement goals and feedback and feedforward control mechanisms in speech production.

Studies of speech motor control are described that support a theoretical framework in which fundamental control variables for phonemic movements are multi-dimensional regions in auditory and somatosensory spaces. Auditory feedback is used to acquire and maintain auditory goals and in the development and function of feedback and feedforward control mechanisms. Several lines of evidence support the idea that speakers with more acute sensory discrimination acquire more distinct goal regions and therefore produce speech sounds with greater contrast. Feedback modification findings indicate that fluently produced sound sequences are encoded as feedforward commands, and feedback control serves to correct mismatches between expected and produced sensory consequences.

Focal manipulations of formant trajectories reveal a role of auditory feedback in the online control of both within-syllable and between-syllable speech timing.

Within the human motor repertoire, speech production has a uniquely high level of spatiotemporal complexity. The production of running speech comprises the traversing of spatial positions with precisely coordinated articulator movements to produce 10-15 sounds/s. How does the brain use auditory feedback, namely the self-perception of produced speech sounds, in the online control of spatial and temporal parameters of multisyllabic articulation? This question has important bearings on the organizational principles of sequential actions, yet its answer remains controversial due to the long latency of the auditory feedback pathway and technical challenges involved in manipulating auditory feedback in precisely controlled ways during running speech. In this study, we developed a novel technique for introducing time-varying, focal perturbations in the auditory feedback during multisyllabic, connected speech. Manipulations of spatial and temporal parameters of the formant trajectory were tested separately on two groups of subjects as they uttered "I owe you a yo-yo." Under these perturbations, significant and specific changes were observed in both the spatial and temporal parameters of the produced formant trajectories. Compensations to spatial perturbations were bidirectional and opposed the perturbations. Furthermore, under perturbations that manipulated the timing of auditory feedback trajectory (slow-down or speed-up), significant adjustments in syllable timing were observed in the subjects' productions. These results highlight the systematic roles of auditory feedback in the online control of a highly over-learned action as connected speech articulation and provide a first look at the properties of this type of sensorimotor interaction in sequential movements.

An investigation of the relation between sibilant production and somatosensory and auditory acuity.

The relation between auditory acuity, somatosensory acuity and the magnitude of produced sibilant contrast was investigated with data from 18 participants. To measure auditory acuity, stimuli from a synthetic sibilant continuum ([s]-[ʃ]) were used in a four-interval, two-alternative forced choice adaptive-staircase discrimination task. To measure somatosensory acuity, small plastic domes with grooves of different spacing were pressed against each participant's tongue tip and the participant was asked to identify one of four possible orientations of the grooves. Sibilant contrast magnitudes were estimated from productions of the words 'said,' 'shed,' 'sid,' and 'shid'. Multiple linear regression revealed a significant relation indicating that a combination of somatosensory and auditory acuity measures predicts produced acoustic contrast. When the participants were divided into high- and low-acuity groups based on their median somatosensory and auditory acuity measures, separate ANOVA analyses with sibilant contrast as the dependent variable yielded a significant main effect for each acuity group. These results provide evidence that sibilant productions have auditory as well as somatosensory goals and are consistent with prior results and the theoretical framework underlying the DIVA model of speech production.

Adaptive auditory feedback control of the production of formant trajectories in the Mandarin triphthong /iau/ and its pattern of generalization.

In order to test whether auditory feedback is involved in the planning of complex articulatory gestures in time-varying phonemes, the current study examined native Mandarin speakers' responses to auditory perturbations of their auditory feedback of the trajectory of the first formant frequency during their production of the triphthong /iau/. On average, subjects adaptively adjusted their productions to partially compensate for the perturbations in auditory feedback. This result indicates that auditory feedback control of speech movements is not restricted to quasi-static gestures in monophthongs as found in previous studies, but also extends to time-varying gestures. To probe the internal structure of the mechanisms of auditory-motor transformations, the pattern of generalization of the adaptation learned on the triphthong /iau/ to other vowels with different temporal and spatial characteristics (produced only under masking noise) was tested. A broad but weak pattern of generalization was observed; the strength of the generalization diminished with increasing dissimilarity from /iau/. The details and implications of the pattern of generalization are examined and discussed in light of previous sensorimotor adaptation studies of both speech and limb motor control and a neurocomputational model of speech motor control.

Perception and production of /r/ allophones improve with hearing from a cochlear implant.

Tongue shape can vary greatly for allophones of /r/ produced in different phonetic contexts but the primary acoustic cue used by listeners, lowered F3, remains stable. For the current study, it was hypothesized that auditory feedback maintains the speech motor control mechanisms that are constraining acoustic variability of F3 in /r/; thus the listener's percept remains /r/ despite the range of articulatory configurations employed by the speaker. Given the potential importance of auditory feedback, postlingually deafened speakers should show larger acoustic variation in /r/ allophones than hearing controls, and auditory feedback from a cochlear implant could reduce that variation over time. To test these hypotheses, measures were made of phoneme perception and of production of tokens containing /r/, stop consonants, and /r/+stop clusters in hearing controls and in eight postlingually deafened adults pre- and postimplant. Postimplant, seven of the eight implant speakers did not differ from the control mean. It was also found that implant users' production of stop and stop+/r/ blend improved with time but the measured acoustic contrast between these was still better in the control speakers than for the implant group even after the implant users had experienced a year of improved auditory feedback.

Sensorimotor adaptation to feedback perturbations of vowel acoustics and its relation to perception.

The role of auditory feedback in speech motor control was explored in three related experiments. Experiment 1 investigated auditory sensorimotor adaptation: the process by which speakers alter their speech production to compensate for perturbations of auditory feedback. When the first formant frequency (F1) was shifted in the feedback heard by subjects as they produced vowels in consonant-vowel-consonant (CVC) words, the subjects' vowels demonstrated compensatory formant shifts that were maintained when auditory feedback was subsequently masked by noise-evidence of adaptation. Experiment 2 investigated auditory discrimination of synthetic vowel stimuli differing in F1 frequency, using the same subjects. Those with more acute F1 discrimination had compensated more to F1 perturbation. Experiment 3 consisted of simulations with the directions into velocities of articulators model of speech motor planning, which showed that the model can account for key aspects of compensation. In the model, movement goals for vowels are regions in auditory space; perturbation of auditory feedback invokes auditory feedback control mechanisms that correct for the perturbation, which in turn causes updating of feedforward commands to incorporate these corrections. The relation between speaker acuity and amount of compensation to auditory perturbation is mediated by the size of speakers' auditory goal regions, with more acute speakers having smaller goal regions.

Effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts.

PURPOSE: To assess the effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts and to evaluate hypotheses arising from a model of speech motor planning. METHOD: The perception and production of vowel and sibilant contrasts were measured in 8 postlingually deafened adults prior to activation of their cochlear implant speech processors, 1 month postactivation, and 1 year postactivation. Measures were taken postactivation both with and without auditory feedback. Contrast measures were also made for a group of speakers with reportedly normal hearing speaking with masked and unmasked auditory feedback. RESULTS: Vowel and sibilant contrasts, measured in the absence of auditory feedback after 1 month of prosthesis use, were diminished compared with their values measured before prosthesis. Contrasts measured in the absence of auditory feedback after 1 year's experience with the prosthesis were increased compared with their values after 1 month's experience. In both time samples, contrasts were enhanced when auditory feedback was restored. CONCLUSION: The provision of prosthetic hearing to postlingually deafened adults impaired their phonemic contrasts at first, as their auditory feedback had novel characteristics. Once auditory feedback became recalibrated with prosthesis use, it could, in turn, revise feedforward commands that control the contrasts in its absence.

Interactions of speaking condition and auditory feedback on vowel production in postlingually deaf adults with cochlear implants.

This study investigates the effects of speaking condition and auditory feedback on vowel production by postlingually deafened adults. Thirteen cochlear implant users produced repetitions of nine American English vowels prior to implantation, and at one month and one year after implantation. There were three speaking conditions (clear, normal, and fast), and two feedback conditions after implantation (implant processor turned on and off). Ten normal-hearing controls were also recorded once. Vowel contrasts in the formant space (expressed in mels) were larger in the clear than in the fast condition, both for controls and for implant users at all three time samples. Implant users also produced differences in duration between clear and fast conditions that were in the range of those obtained from the controls. In agreement with prior work, the implant users had contrast values lower than did the controls. The implant users' contrasts were larger with hearing on than off and improved from one month to one year postimplant. Because the controls and implant users responded similarly to a change in speaking condition, it is inferred that auditory feedback, although demonstrably important for maintaining normative values of vowel contrasts, is not needed to maintain the distinctiveness of those contrasts in different speaking conditions.

Time course of speech changes in response to unanticipated short-term changes in hearing state.

The timing of changes in parameters of speech production was investigated in six cochlear implant users by switching their implant microphones off and on a number of times in a single experimental session. The subjects repeated four short, two-word utterances, /dV1n#SV2d/ (S = /s/ or /S/), in quasi-random order. The changes between hearing and nonhearing states were introduced by a voice-activated switch at V1 onset. "Postural" measures were made of vowel sound pressure level (SPL), duration, F0; contrast measures were made of vowel separation (distance between pair members in the formant plane) and sibilant separation (difference in spectral means). Changes in parameter values were averaged over multiple utterances, lined up with respect to the switch. No matter whether prosthetic hearing was blocked or restored, contrast measures for vowels and sibilants did not change systematically. Some changes in duration, SPL and F0 were observed during the vowel within which hearing state was changed, V1, as well as during V2 and subsequent utterance repetitions. Thus, sound segment contrasts appear to be controlled differently from the postural parameters of speaking rate and average SPL and F0. These findings are interpreted in terms of the function of hypothesized feedback and feedforward mechanisms for speech motor control.