Voice Disorders and Speech Intelligibility in Developmental Dysarthria: Influence of Speech Task

Impairment of the phonatory subsystem is a common feature of developmental dysarthria and may contribute to reduced speech intelligibility. However, voice quality is known to vary as a function of speech task, and the relationship between phonatory functioning and intelligibility across elicitation contexts remains poorly understood. This study aimed to (1) examine speech task effects on acoustic measures of voice quality, and (2) investigate task-specific relationships between voice quality and intelligibility in children and adolescents with developmental dysarthria.

Participants with developmental dysarthria (n = 31, mean age: 12;3 years) produced speech across three tasks: sustained phonation (/a/), single-word production (picture naming), and spontaneous speech (picture description). Acoustic measures included cepstral peak prominence (CPP), jitter, shimmer, and harmonic-to-noise ratio (HNR), adapted for connected speech contexts. Speech intelligibility was assessed via transcription for single-word productions and listener ratings for connected speech samples. Perceptual voice quality was evaluated using the GRBAS Grade (G) component for sustained phonation. Linear mixed-effects models examined task effects on voice quality and relationships between acoustic measures and intelligibility.

Significant task effects were observed for all acoustic measures. Sustained phonation yielded the most favorable voice quality, followed by connected speech, with single-word productions demonstrating the poorest vocal quality. Acoustic measures of sustained phonation were significantly associated with perceptual ratings, supporting their validity. No significant relationships were found between acoustic voice measures and intelligibility at either the word or connected speech levels.

Voice quality in developmental dysarthria is strongly influenced by speech task, reflecting differences in motor demands and subsystem integration. Perceptual ratings aligned with acoustic measures during sustained phonation; however, acoustic indices across tasks were not directly associated with intelligibility outcomes. These findings underscore the importance of task selection in voice assessment and suggest that phonatory impairment may not directly capture functional communication outcomes in developmental dysarthria.