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/).