Relationships between acoustic and perceptual measures of stress in nonwords produced by children with developmental apraxia of speech and children with phonological disorders

Abstract

This study investigated relationships between acoustic measures of stress in nonwords produced by children with suspected developmental apraxia of speech (sDAS) and children with phonological disorders (PD), and perceptual judgments made by trained listeners. Five children with sDAS and five children with PD produced multiple tokens of eight disyllabic nonwords with iambic and trochaic stress patterns. Measures of vowel duration, f0, and intensity were made. Children from both groups produced acoustic differences between stressed and stressless syllables. In a perception experiment, 10 listeners judged whether tokens were produced with stress on the initial or final syllable. Listeners judged that children with sDAS accurately matched target stress contours less often than children with PD. The proportion of listeners judging that a word was produced with final syllable stress was used as the dependant variable in a regression, in which the ratio of vowel duration, f0, and intensity between the two syllables served as the independent variables. All three variables predicted a significant proportion of variance in listener judgments, although the overall proportion of variance accounted for was low (R2=0.212). Thus, children with sDAS are able to produce contrasts between stressed and stressless syllables, but these are often imperceptible to listeners.