Transcription-based and acoustic analyses of rhotic vowels produced by children with and without speech sound disorders: Further analyses from the Memphis Vowel Project

Abstract

The acquisition of rhotic monophthongs (/ɝ/ and /ɚ/) and diphthongs (/ɪ͡ɚ, ɛ͡ɚ, ɔ͡ɚ and ɑ͡ɚ/) was examined in 3- and 4-year-old children with and without speech sound disorders (SSDs), using both transcription-based and acoustic analyses. African-American (AA) and European-American (EA) participants (n = 40) with and without SSD were selected from archival data collected as part of the Memphis Vowel Project. Dialect variation influenced rhotic vowels differently for EA and AA children, thus their data were reported separately. Transcription-based analyses showed wide variation in the accuracy of different rhotic vowels. The most frequent error pattern for children with SSD was Derhoticization to a Back Rounded Vowel (e.g. /ɝ/ → [ʊ]; /ɪ͡ɚ/ → [ɪ͡о]). Rhotic diphthong reduction errors were less frequent; however, Coalesence (/ɑ͡ɚ/ → [ɔ]) was often observed for /ɑ͡ɚ/. F2, F3 and F3-F2 spectral movement patterns revealed differences between productions transcribed as correct and incorrect.

Acoustic Characteristics of Rhotic Vowel Productions of Young Children

“…Debate still exists whether to consider postvocalic rhotics as rhotic vowels or as a combination of a nonrhotic vowel with a rhotic consonant. In the current paper, to be consistent with findings that showed completely merged acoustic patterns of the pre-rhotic vowel and the following rhotic consonant [6] and other clinical and acoustic research on rhotic sounds [7][8][9][10][11][12], all vocalic and postvocalic rhotic sounds are considered as rhotic vowels. Among rhotic vowels, those that appear in a nucleus of the syllable are referred to as rhotic monophthongs and were transcribed using [ɜ˞] when stressed and [ə˞] when unstressed (e.g., /bɜ˞d/ for bird, / zɪpɚ/ for zipper).…”

“…Target words included 36 single words containing both stressed and unstressed rhotic monophthongs ([ɝ] and [ɚ]) and four different rhotic diphthongs (/ɪ͡ɚ/, /ɛ͡ɚ/, /ɔ͡ɚ/,and/ɑ͡ɚ/) in both open and closed syllables (Table 2). These words were taken from a set of 62 words elicited as part of the larger project on rhotic sounds [8, 30]. The full set of words also included 7 words containing rhotic consonants (3 /ɹ/ singleton and 4 /ɹ/ clusters), 13 control words containing nonrhotic vowels (10 monophthongs /i, ɪ, e, ɛ, æ, u, ʊ, o, ɑ, ʌ/ and 3 diphthongs /ɑ͡ɪ, ɑ͡ʊ, o͡ɪ/), as well as 6 words containing word-initial nonrhotic consonant /w/ in singletons and clusters (3 /w/ singleton and 3 /w/ clusters).…”

“…That is, although all of the productions examined were judged to be perceptually acceptable, rhotic vowels produced by children with high rhotic vowel and consonant accuracy were predicted to show a greater degree of rhoticity as compared to those of children with lower overall rhotic sound accuracy. Second, (i) for stress level, no difference in F3 and F3-F2 was expected, while (ii) some effect of phonetic context, difference in F3 and F3-F2 among rhotic diphthongs of different prerhotic vowel types as observed in both young children [11] and adult productions [8], was expected. Lastly, for the (iii) effect of vowel complexity, similar F3 and F3-F2 patterns between rhotic diphthongs and rhotic monophthongs were expected.…”