Acoustic and perceptual correlates of stress in nonwords produced by children with suspected developmental apraxia of speech and children with phonological disorder

Previous research (L. Shriberg, D. Aram, & J. Kwiatkowski, 1997b, 1997c) has suggested that accuracy in producing linguistic stress reliably distinguishes between children with suspected developmental apraxia of speech (sDAS) and children with phonological disorder (PD). The current investigation tested this hypothesis by examining acoustic correlates of stress in trochaic (strong-weak) and iambic (weak-strong) nonwords produced by 5 children in each of these 2 groups. Four measures relating to stress production were examined: vowel duration, fundamental frequency (f₀) at vowel midpoint, timing of the f₀ peak relative to vowel onset, and intensity at vowel midpoint. In addition, perceptual judgments of accuracy of stress production were obtained. No group differences in the production of stress were found; however, listeners judged that the nonword repetitions of children with sDAS matched the target stress contour less often than did the repetitions of children with PD. Multiple regression analyses found that mean vowel duration, as well as the relative duration and relative f₀ of stressed and stressless syllables, predicted listeners' judgments of stress, although these variables only accounted for a small proportion of variance (21.8%). Thus, children with sDAS were able to produce acoustic differences between stressed and stressless syllables, but these differences were not consistently perceptible to listeners.