Rhotic vowel accuracy and error patterns in young children with and without Speech Sound Disorders

Classification of accurate and misarticulated /r/ for ultrasound biofeedback using tongue part displacement trajectories

Ultrasound biofeedback therapy (UBT), which incorporates real-time imaging of tongue articulation, has demonstrated generally positive speech remediation outcomes for individuals with residual speech sound disorder (RSSD). However, UBT requires high attentional demands and may therefore benefit from a simplified display of articulation targets that are easily interpretable and can be compared to real-time articulation. Identifying such targets requires automatic quantification and analysis of movement features relevant to accurate speech production. Our image-analysis program TonguePART automatically quantifies tongue movement as tongue part displacement trajectories from midsagittal ultrasound videos of the tongue, with real-time capability. The present study uses such displacement trajectories to compare accurate and misarticulated American-English rhotic /ɑr/ productions from 40 children, with degree of accuracy determined by auditory perceptual ratings. To identify relevant features of accurate articulation, support vector machine (SVM) classifiers were trained and evaluated on several candidate data representations. Classification accuracy was up to 85%, indicating that quantification of tongue part displacement trajectories captured tongue articulation characteristics that distinguish accurate from misarticulated production of /ɑr/. Regression models for perceptual ratings were also compared. The simplest data representation that retained high predictive ability, demonstrated by high classification accuracy and strong correlation between observed and predicted ratings, was displacements at the midpoint of /r/ relative to /ɑ/ for the tongue dorsum and blade. This indicates that movements of the dorsum and blade are especially relevant to accurate production of /r/, suggesting that a predictive parameter and biofeedback target based on this data representation may be usable for simplified UBT.

Acoustic Characteristics of Rhotic Vowel Productions of Young Children

AIMS

This study examined the acoustic characteristics of perceptually acceptable rhotic vowels produced by young children with and without speech sound disorders (SSDs). Productions were analyzed in relation to the overall rhotic proficiency level of each child, as determined by rhotic vowel and consonant accuracy. The effect of the surrounding phonetic contexts on acoustic realization of rhotic vowels was also examined.

METHODS

Participants included 18 children aged 2-6 years with and without SSD, grouped by overall rhotic sound proficiency (high rhotic proficiency: ≥70% correct rhotic consonants and vowels; intermediate rhotic proficiency: ≤30% correct rhotic consonants, but ≥70% correct rhotic vowels; low rhotic proficiency: ≤30% correct rhotic consonants and vowels). Target sounds included stressed and unstressed rhotic monophthongs ([ɝ] and [ɚ], respectively) and 4 rhotic diphthongs that differ by pre-rhotic vowel type (/ɪ͡ɚ/, /ɛ͡ɚ/, /ɔ͡ɚ/, /ɑ͡ɚ/). F3 and F3-F2 measures were compared across groups and contexts.

RESULTS

No significant differences in F3 and F3-F2 by rhotic sound proficiency group were found in rhotic vowels produced by children with above 70% rhotic vowel accuracy, regardless of their proficiency with rhotic consonants. Acoustic patterns differed by phonetic contexts, but the effect varied by rhotic sound proficiency group.

CONCLUSION

Results showed that once children learn to produce rhotic vowels, they show a comparable degree of rhoticity as those produced by children with high rhotic vowel and consonant accuracy. Results also suggest that rhotic sounds develop earlier in certain phonetic contexts than in others (e.g., [ɝ] before [ɚ]; /ɪ͡ɚ/ and /ɑ͡ɚ/ before /ɔ͡ɚ/).