Are Specific Language Impairment and Dyslexia Distinct Disorders? Purpose: The purpose of this study was to determine whether specific language impairment (SLI) and dyslexia are distinct developmental disorders. Method: Study 1 investigated the overlap between SLI identified in kindergarten and dyslexia identified in 2nd, 4th, or 8th grades in a representative sample of 527 children. Study 2 examined ... Research Article
EDITOR'S AWARD
Research Article  |   December 2005
Are Specific Language Impairment and Dyslexia Distinct Disorders?
 
Author Affiliations & Notes
  • Hugh W. Catts
    University of Kansas, Lawrence
  • Suzanne M. Adlof
    University of Kansas, Lawrence
  • Tiffany P. Hogan
    University of Kansas, Lawrence
  • Susan Ellis Weismer
    University of Wisconsin—Madison
  • Corresponding author: e-mail: catts@ku.edu
Article Information
Language Disorders / Specific Language Impairment / Reading & Writing Disorders / Language / Research Articles
Research Article   |   December 2005
Are Specific Language Impairment and Dyslexia Distinct Disorders?
Journal of Speech, Language, and Hearing Research, December 2005, Vol. 48, 1378-1396. doi:10.1044/1092-4388(2005/096)
History: Received October 26, 2004 , Accepted March 13, 2005
 
Journal of Speech, Language, and Hearing Research, December 2005, Vol. 48, 1378-1396. doi:10.1044/1092-4388(2005/096)
History: Received October 26, 2004; Accepted March 13, 2005

Purpose: The purpose of this study was to determine whether specific language impairment (SLI) and dyslexia are distinct developmental disorders.

Method: Study 1 investigated the overlap between SLI identified in kindergarten and dyslexia identified in 2nd, 4th, or 8th grades in a representative sample of 527 children. Study 2 examined phonological processing in a subsample of participants, including 21 children with dyslexia only, 43 children with SLI only, 18 children with SLI and dyslexia, and 165 children with typical language/reading development. Measures of phonological awareness and nonword repetition were considered.

Results: Study 1 showed limited but statistically significant overlap between SLI and dyslexia. Study 2 found that children with dyslexia or a combination of dyslexia and SLI performed significantly less well on measures of phonological processing than did children with SLI only and those with typical development. Children with SLI only showed only mild deficits in phonological processing compared with typical children.

Conclusions: These results support the view that SLI and dyslexia are distinct but potentially comorbid developmental language disorders. A deficit in phonological processing is closely associated with dyslexia but not with SLI when it occurs in the absence of dyslexia.

Acknowledgments
This study was supported by a grant from the National Institute on Deafness and Other Communication Disorders (1-P50-DC02726-04). The completion of this study was aided considerably by a valuable research team comprising the following: Bruce Tomblin, Xuyang Zhang, Marc Fey, Paula Buckwalter, Marlea O’Brien, Connie Ferguson, Jodi Schwartz, Juanita Limas, and Amy Kundel. Appreciation is also extended to Holly Storkel and David Slegers for their assistance.
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