Developmental Apraxia of Speech III. A Subtype Marked by Inappropriate Stress Research Article
Research Article  |   April 01, 1997
Developmental Apraxia of Speech
 
Author Affiliations & Notes
  • Lawrence D. Shriberg
    University of Wisconsin-Madison
  • Dorothy M. Aram
    Emerson College Boston, MA
  • Joan Kwiatkowski
    University of Wisconsin-Madison
Article Information
Speech, Voice & Prosodic Disorders / Apraxia of Speech & Childhood Apraxia of Speech / Speech, Voice & Prosody / Language / Research Articles
Research Article   |   April 01, 1997
Developmental Apraxia of Speech
Journal of Speech, Language, and Hearing Research, April 1997, Vol. 40, 313-337. doi:10.1044/jslhr.4002.313
History: Received June 4, 1996 , Accepted October 13, 1996
 
Journal of Speech, Language, and Hearing Research, April 1997, Vol. 40, 313-337. doi:10.1044/jslhr.4002.313
History: Received June 4, 1996; Accepted October 13, 1996

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.

Acknowledgments
This research was supported by a grant from the U.S. Public Health Service, NIDCD DC00496. We are extremely grateful to five colleagues who, in the best spirit of collegial collaboration, provided audiotaped case examples and case study data: Barbara Davis, Penelope Hall, Deborah Hayden, Barbara Lewis, and Shelley Velleman. Special thanks to Diane Austin for her proficient assistance with the computational analyses and manuscript processing. Finally, thanks to the following persons who provided incisive editorial comment on earlier drafts of this work: Peter Flipsen Jr., Frederic Gruber, Penelope Hall, Katharine Odell, Anne Ozanne, Elizabeth Shriberg, and Shelley Velleman.
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