Tongue-to-palate contact patterns and variability of four English consonants in an /i/ vowel environment

Articulatory Variability is Reduced by Repetition and Predictability

Repeating the movements associated with activities such as drawing or sports typically leads to improvements in kinematic behavior: these movements become faster, smoother, and exhibit less variation. Likewise, practice has also been shown to lead to faster and smoother movement trajectories in speech articulation. However, little is known about its effect on articulatory variability. To address this, we investigate the extent to which repetition and predictability influence the articulation of the frequent German word "sie" [zi] (they). We find that articulatory variability is proportional to speaking rate and the duration of [zi], and that overall variability decreases as [zi] is repeated during the experiment. Lower variability is also observed as the conditional probability of [zi] increases, and the greatest reduction in variability occurs during the execution of the vocalic target of [i]. These results indicate that practice can produce observable differences in the articulation of even the most common gestures used in speech.

Model-based inverse estimation for active contraction stresses of tongue muscles using 3D surface shape in speech production

This paper presents a novel inverse estimation approach for the active contraction stresses of tongue muscles during speech. The proposed method is based on variational data assimilation using a mechanical tongue model and 3D tongue surface shapes for speech production. The mechanical tongue model considers nonlinear hyperelasticity, finite deformation, actual geometry from computed tomography (CT) images, and anisotropic active contraction by muscle fibers, the orientations of which are ideally determined using anatomical drawings. The tongue deformation is obtained by solving a stationary force-equilibrium equation using a finite element method. An inverse problem is established to find the combination of muscle contraction stresses that minimizes the Euclidean distance of the tongue surfaces between the mechanical analysis and CT results of speech production, where a signed-distance function represents the tongue surface. Our approach is validated through an ideal numerical example and extended to the real-world case of two Japanese vowels, /ʉ/ and /ɯ/. The results capture the target shape completely and provide an excellent estimation of the active contraction stresses in the ideal case, and exhibit similar tendencies as in previous observations and simulations for the actual vowel cases. The present approach can reveal the relative relationship among the muscle contraction stresses in similar utterances with different tongue shapes, and enables the investigation of the coordination of tongue muscles during speech using only the deformed tongue shape obtained from medical images. This will enhance our understanding of speech motor control.

Speaking Tongues Are Actively Braced

PURPOSE

Bracing of the tongue against opposing vocal-tract surfaces such as the teeth or palate has long been discussed in the context of biomechanical, somatosensory, and aeroacoustic aspects of tongue movement. However, previous studies have tended to describe bracing only in terms of contact (rather than mechanical support), and only in limited phonetic contexts, supporting a widespread view of bracing as an occasional state, peculiar to specific sounds or sound combinations.

METHOD

The present study tests the pervasiveness and effortfulness of tongue bracing in continuous English speech passages using electropalatography and 3-D biomechanical simulations.

RESULTS

The tongue remains in continuous contact with the upper molars during speech, with only rare exceptions. Use of the term bracing (rather than merely contact) is supported here by biomechanical simulations showing that lateral bracing is an active posture requiring dedicated muscle activation; further, loss of lateral contact for onset /l/ allophones is found to be consistently accompanied by contact of the tongue blade against the anterior palate. In the rare instances where direct evidence for contact is lacking (only in a minority of low vowel and postvocalic /l/ tokens), additional biomechanical simulations show that lateral contact is maintained against pharyngeal structures dorsal to the teeth.

CONCLUSION

Taken together, these results indicate that tongue bracing is both pervasive and active in running speech and essential in understanding tongue movement control.

Lateral bracing of the tongue during the onset phase of alveolar stops: an EPG study

Although raising the sides of the tongue to form a seal with the palate and upper teeth--lateral bracing--plays a key role in controlling airflow direction, providing overall tongue stability and building up oral pressure during alveolar consonant production, details of this articulatory gesture remain poorly understood. This study examined the dynamics of lateral bracing during the onset of alveolar stops /t/, /d/, /n/ produced by 15 typical English-speaking adults using electropalatography. Percent tongue palate contact in the lateral regions over a 150-ms period from the preceding schwa to stop closure was measured. Rapid rising of the sides of the tongue from the back towards the front during the 50-ms period before closure was observed, with oral stops showing significantly more contact than nasal stops. This feature corresponds to well-documented formant transitions detectable from acoustic analysis. Possible explanations for increased contact for oral stops and clinical implications are discussed.

Positional targets for lingual consonants defined using electromagnetic articulography

The study examined the positional targets for lingual consonants defined using a point-parameterized approach with Wave (NDI, Waterloo, ON, Canada). The overall goal was to determine which consonants had unique tongue positions with respect to other consonants. Nineteen talkers repeated vowel-consonant-vowel (VCV) syllables that included consonants /t, d, s, z, , k, g/ in symmetrical vowel contexts /i, u, a/, embedded in a carrier phrase. Target regions for each consonant, characterized in terms of x,y,z tongue positions at the point of maximum tongue elevation, were extracted. Distances and overlaps were computed between all consonant pairs and compared to the distances and overlaps of their contextual targets. Cognates and postalveolar homorganics were found to share the location of their target regions. On average, alveolar stops showed distinctively different target regions than alveolar fricatives, which in turn showed different target region locations than the postalveolar consonants. Across talker variability in target locations was partially explained by differences in habitual speaking rate and hard palate characteristics.

Intra-speaker variability in palatometric measures of consonant articulation

Electropalatometry is a useful clinical and research tool for measuring linguapalatal contact. The goal of this study was to examine intra-speaker variability in performance. Twenty individuals spoke VCV nonsense words using a schwa in the initial position, the 15 palatal consonants, and three corner vowels, /a/, /i/, /u/. A variability index was created to examine speaker consistency. Different aspects of articulation (i.e. place, manner, voicing, coarticulation) were compared. Significant differences for variability were found for place of articulation in the /i/ vowel context and for manner of articulation in the /a/ vowel context. Also for the /a/ vowel, significant differences were found between the commonly misarticulated /l/, /r/, and /s/. The data reveal differences in production variability across sounds within an individual, as well as from one speaker to another. This knowledge of typical performance may guide the interpretation of data from disordered speakers in future studies.

LEARNING OUTCOMES

The reader will be able to: (1) Describe how articulatory performance and variability can be assessed with the palatometer; (2) Describe which sounds are typically most or least variable in their production; and (3) Understand the significance of individual speaker differences in normal consonant articulation.

Electropalatography treatment for articulation impairment in children with dysarthria post-traumatic brain injury

PRIMARY OBJECTIVE

Dysarthria with severe articulatory impairment is a common and debilitating sequelae following severe traumatic brain injury (TBI). Eectropalatography (EPG) is an instrumental treatment technique allowing visual feedback of tongue to palate movement during real time articulation. The present study investigated the effectiveness of EPG in treating the articulatory component of dysarthria post-TBI.

STUDY DESIGN/METHODS

The articulatory component of dysarthria post-TBI was treated once per week with EPG over a 10-week period in three adolescents (aged 14 years 10 months-15 years 1 month). A multiple case series ABA treatment design was used. Perceptual (articulation, intelligibility) and EPG (spatial, durational) assessments were conducted pre- and post-treatment to determine outcome.

RESULTS/DISCUSSION

Perceptual improvement was noted for phoneme precision and length. Spatial EPG measures confirmed increased precision of phoneme production. No clear pattern of change for phoneme duration occurred. Intelligibility increased at word and sentence level, with little change reported in everyday speech intelligibility.

CONCLUSION

This preliminary study indicates that EPG treatment may be effective for improving speech at the isolated phoneme, word or sentence level of articulation. These preliminary results are encouraging, being the first study to report speech changes post-treatment in participants with severe TBI and persistent dysarthria. Further research is required, however, in order to understand the regenerative capacity of articulatory function post-brain injury and to determine optimal treatment parameters for achieving generalization of therapy to everyday connected speech.

Electropalatographic assessment of tongue-to-palate contact patterns and variability in children, adolescents, and adults

PURPOSE

To investigate the developmental time course of tongue-to-palate contact patterns during speech from childhood to adulthood using electropalatography (EPG) and a comprehensive profile of data analysis.

METHOD

Tongue-to-palate contacts were recorded during productions of /t/, /l/, /s/, and /k/ in 48 children, adolescents and adults (aged 6-38 years) using the Reading Electropalatograph system.

RESULTS

A protracted course of development for lingual control was indicated, with significant changes occurring until age 11 years; the adolescent period was in turn characterized by continual refinement of articulatory control. With maturity, a reduction in the amount of palatal contact and an anterior shift in the place of articulation was evident during anterior consonant productions, whereas the tongue-back-to-palate contact pattern became more consistent for the velar stop /k/.

CONCLUSION

These results support that maturation of the speech motor system is nonuniform.

Speech production in Parkinson's disease: I. An electropalatographic investigation of tongue-palate contact patterns

Previous studies have indicated that consonant imprecision in Parkinson's disease (PD) may result from a reduction in amplitude of lingual movements or articulatory undershoot. While this has been postulated, direct measurement of the tongue's contact with the hard palate during speech production has not been undertaken. Therefore, the present study aimed to use electropalatography (EPG) to determine the exact nature of tongue-palate contact in a group of individuals with PD and consonant imprecision (n = 9). Furthermore, the current investigation also aimed to compare the results of the participants with PD to a group of aged (n = 7) and young (n = 8) control speakers to determine the relative contribution of ageing of the lingual musculature to any articulatory deficits noted. Participants were required to read aloud the phrase 'I saw a _ today' with the artificial palate in-situ. Target words included the consonants /l/, /s/ and /t/ in initial position in both the /i/ and /a/ vowel environments. Phonetic transcription of phoneme productions and description of error types was completed. Furthermore, representative frames of contact were employed to describe the features of tongue-palate contact and to calculate spatial palatal indices. Results of the perceptual investigation revealed that perceived undershooting of articulatory targets distinguished the participant group with PD from the control groups. However, objective EPG assessment indicated that undershooting of the target consonant was not the cause of the perceived articulatory errors. It is, therefore, possible that reduced pressure of tongue contact with the hard palate, sub-lingual deficits or impaired articulatory timing resulted in the perceived undershooting of the target consonants.