Impact of Prosodic Strategies on Vowel Intelligibility in Childhood Motor Speech Impairment

Vowel production contributes to the intelligibility of individuals with motor speech disorders. In adults with dysarthria, rate reduction and increased loudness have been shown to improve intelligibility partly because of changes in vowel production. The impact of prosodic modulation on vowel acoustics and intelligibility in children with motor speech impairment (MSI), however, is unclear. The current investigation aimed to provide perceptual and acoustic data from three children (ages 3 years, 6 months to 8 years, 6 months) with motor programming deficits producing utterances in four conditions: (1) habitual, (2) increased loudness, (3) slowed rate, and (4) emphatic stress. Additional acoustic data were collected from three healthy age-matched control participants (ages 4 years, 1 month to 8 years, 10 months). For each condition, utterances containing three corner vowels (/i/, /a/, /u/) were elicited using an audio-visualization technique. Perceptual intelligibility was based on judgments of 12 unfamiliar listeners. The impact of prosodic strategies varied across speakers, with two children with MSI demonstrating increased vowel intelligibility in at least one modulation condition. Acoustic analyses included first (F1) and second (F2) formant extraction and comparison of variance across conditions. F2 variance was greater for the children with MSI. These preliminary findings shed light on the interaction between prosodic modulation and intelligibility in childhood MSI and warrant further investigation.