Two prior studies in this series (Shriberg, Aram, & Kwiatkowski, 1997a, 1997b) address the premise that children with developmental
apraxia of speech (
DAS) can be differentiated from children with
speech delay (SD) on the basis of one or more reliable differences in their speech. The first study compared segmental and prosody-voice profiles of a group of 14 children with suspected
DAS to profiles of 73 children with SD. Results suggest that the only linguistic domain that differentiates some children with suspected
DAS from those with SD is inappropriate stress. The second study cross-validated these findings, using retrospective data from a sample of 20 children with suspected
DAS evaluated in a university phonology clinic over a 10-year period. The present study is of particular interest because it cross-validates the prior stress findings, using conversational speech samples from 19 children with suspected
DAS provided by five
DAS researchers at geographically diverse diagnostic facilities in North America. Summed across the three studies, 52% of 48 eligible samples from 53 children with suspected
DAS had inappropriate stress, compared to 10% of 71 eligible samples from 73 age-matched children with
speech delay of unknown origin. Discussion first focuses on the implications of stress findings for theories of the origin and nature of
DAS. Perspectives in psycholinguistics, neurolinguistics, and developmental biolinguistics lead to five working hypotheses pending validation in ongoing studies: (a) inappropriate stress is a diagnostic marker for at least one subtype of
DAS, (b) the psycholinguistic loci of inappropriate stress in this subtype of
DAS are in phonological representational processes, (c) the proximal origin of this subtype of
DAS is a neurogenically specific deficit, (d) the distal origin of this form of
DAS is an inherited genetic polymorphism, and (e) significant differences between acquired
apraxia of speech in adults and findings for this subtype of
DAS call into question the inference that it is an apractic, motor speech disorder. Concluding discussion considers implications of these findings for research in
DAS and for clinical practice.