Acoustic vowel analysis and speech intelligibility in young adult Hebrew speakers: Developmental dysarthria versus typical development

Abstract

Background: Developmental dysarthria is a motor speech impairment commonly characterized by varying levels of reduced speech intelligibility. The relationship between intelligibility deficits and acoustic vowel space among these individuals has long been noted in the literature, with evidence of vowel centralization (e.g., in English and Mandarin). However, the degree to which this centralization occurs and the intelligibility-acoustic relationship is maintained in different vowel systems has yet to be studied thoroughly. In comparison with American English, the Hebrew vowel system is significantly smaller, with a potentially smaller vowel space area, a factor that may impact upon the comparisons of the acoustic vowel space and its correlation with speech intelligibility. Data on vowel space and speech intelligibility are particularly limited for Hebrew speakers with motor speech disorders. Aims: To determine the nature and degree of vowel space centralization in Hebrew-speaking adolescents and young adults with dysarthria, in comparison with typically developing (TD) peers, and to correlate these findings with speech intelligibility scores. Methods & Procedures: Adolescents and young adults with developmental dysarthria (secondary to cerebral palsy (CP) and other motor deficits, n = 17) and their TD peers (n = 17) were recorded producing Hebrew corner vowels within single words. For intelligibility assessments, naïve listeners transcribed those words produced by speakers with CP, and intelligibility scores were calculated. Outcomes & Results: Acoustic analysis of vowel formants (F1, F2) revealed a centralization of vowel space among speakers with CP for all acoustic metrics of vowel formants, and mainly for the formant centralization ratio (FCR), in comparison with TD peers. Intelligibility scores were correlated strongly with the FCR metric for speakers with CP. Conclusions & Implications: The main results, vowel space centralization for speakers with CP in comparison with TD peers, echo previous cross-linguistic results. The correlation of acoustic results with speech intelligibility carries clinical implications. Taken together, the results contribute to better characterization of the speech production deficit in Hebrew speakers with motor speech disorders. Furthermore, they may guide clinical decision-making and intervention planning to improve speech intelligibility.

Speech treatment for Hebrew‐speaking adolescents and young adults with developmental dysarthria: A comparison of mSIT and Beatalk

“…Severity was confirmed by comparable pre‐treatment intelligibility scores, t (15) = 0.33, p = 0.75. Participant data for both treatment groups are listed in Table 2 (participant data were also reported previously by Carl & Icht (2021). A review of these data demonstrates that the groups were not matched with regard to gender; however, the literature indicates that this factor may not be associated with intelligibility deficits (Whitehill & Ciocca, 2000).…”

“…For the words from which vowels were extracted, see Table 3. For further details of measure calculation, see Carl and Icht (2021: appx B): First and second formants (F1, F2): A comparison of vowel formants across all three corner vowels (/a/, /i/, /u/) from pre‐ to post‐treatment was conducted, in order to determine any change in vowel space area (e.g., Levy et al., 2021; Mou et al., 2019). Triangular vowel space area ( t VSA): The area of the acoustic space (F1 × F2) enclosed by the three corner vowels (/a/, /i/, /u/), with formants averaged across multiple repetitions of each vowel.…”

“…These measures were recorded during a variety of speech tasks in the assessment sessions (pre‐ and post‐treatment), using a high‐quality digital recorder (Philips DVT4010 audio recorder). Following Carl & Icht, 2021, the recorder was held approximately 8 cm from the participant's mouth, with a slight tilt toward the participant. The distance between the recorder and the participant's mouth was maintained during the recording.…”

“…Listeners were also given a practice listening trial, so that volume adjustments could be made prior to listening to the speaker recordings. For a detailed description of the procedures, see Carl and Icht (2021). The number of correctly transcribed words was divided by the total number of words (38), to yield a single score (%) of intelligibility.…”

“…‘Dysarthria’ is a general term for a group of motor‐based speech disorders in which impaired functioning is noted in one or more of the speech subsystems (respiration, phonation, articulation, resonance and prosody), resulting in reduced speech intelligibility (Duffy, 2013). Many individuals with developmental dysarthria, commonly associated with cerebral palsy (CP) (Mei et al., 2014), demonstrate intelligibility deficits that continue from childhood into adolescence and adulthood (Carl & Icht, 2021; Lee et al., 2014; Platt et al., 1980). These impairments negatively affect daily functioning and participation within social and communicative contexts (Mei et al., 2014).…”