Acoustic characteristics of three English semivowels /l, ɹ, w/ and vowels in young children with and without speech sound disorders.

Purpose: The aim of the current study is to examine if the relationship among three semivowel sounds (/l, ɹ, w/) and between the semivowel and the following vowel differs by children's overall speech proficiency, and if this relationship affects listeners' perceptual judgment of the liquid sounds (/l, ɹ/). The acoustic proximity among the three semivowel sounds and the acoustic characteristics of the following vowel sounds were examined by each child speaker's overall speech sound proficiency and their semivowel accuracy.

Methods: A total of 21 monolingual English-speaking children with and without speech sound disorders produced monosyllabic words that include target semivowel sounds in word-initial position in different vowel contexts. Participants were divided into three groups based on overall speech proficiency, as measured by diagnostic status and score on the Goldman-Fristoe Test of Articulation - 3rd Edition. Each semivowel and vowel production was transcribed for accuracy, and F2 and F3 values were extracted at the semivowel midpoints to calculate Euclidean distances (ED) between the three semivowel pairs (/l-w/, /l-ɹ/, and /ɹ-w/). F1 and F2 values extracted at the vowel midpoint were used to examine the characteristics of vowels following the semivowels.

Results: Children with typically developing speech with the highest overall speech proficiency demonstrated the largest ED values between all the three semivowel pairs. Larger ED values were also related to a greater likelihood of semivowels /l/ and /ɹ/ being judged as perceptually acceptable. Acoustic characteristics of the following vowels did not differ across children of varying levels of speech proficiency, but did differ by the preceding semivowel context.

Conclusions: Acoustic distinction of semivowels differs across children with varying levels of speech proficiency and is predictive of judgements of semivowel accuracy. Acoustic characteristics of the vowels were influenced by the preceding semivowel target, indicating the presence of coarticulation across the semivowel-vowel sequences. Findings support intervention approaches that pair semivowel targets to train children to produce acoustic differentiation between semivowels.