Is phonology bypassed in normal or dyslexic development? |
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| Authors: | Bruce F Pennington Dianne L Lefly Guy C Van Orden Myra O Bookman Shelley D Smith |
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| Institution: | (1) University of Colorado School of Medicine, Denver, Colorado;(2) University of Colorado at Denver, Denver, Colorado;(3) Boystown Institute for Communication Disorders in Children, Omaha, Nebraska |
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| Abstract: | A pervasive assumption in most accounts of normal reading and spelling development is that phonological coding is important
early in development but is subsequently superseded by faster, orthographic coding which bypasses phonology. We call this
assumption, which derives from dual process theory, the developmental bypass hypothesis. The present study tests four specific
predictions of the developmental bypass hypothesis by comparing dyslexics and nondyslexics from the same families in a cross-sectional
design. The four predictions are: 1) That phonological coding skill develops early in normal readers and soon reaches asymptote,
whereas orthographic coding skill has a protracted course of development; 2) that the correlation of adult reading or spelling
performance with phonological coding skill is considerably less than the correlation with orthographic coding skill; 3) that
dyslexics who are mainly deficient in phonological coding skill should be able to bypass this deficit and eventually close
the gap in reading and spelling performance; and 4) that the greatest differences between dyslexics and developmental controls
on measures of phonological coding skill should be observed early rather than late in development.
None of the four predictions of the developmental bypass hypothesis were upheld. Phonological coding skill continued to develop
in nondyslexics until adulthood. It accounted for a substantial (32–53 percent) portion of the variance in reading and spelling
performance in adult nondyslexics, whereas orthographic coding skill did not account for a statistically reliable portion
of this variance. The dyslexics differed little across age in phonological coding skill, but made linear progress in orthographic
coding skill, surpassing spelling-age (SA) controls by adulthood. Nonetheless, they didnot close the gap in reading and spelling performance. Finally, dyslexics were significantly worse than SA (and Reading Age RA])
controls in phonological coding skill only in adulthood.
This research was supported by the following grants to the first author: A NIMH RSDA (MH00419-05) and project grants from
NIMH (MH38820-04), NICHD (HD19423-02) and the March of Dimes (12-135). Author Smith’s work was supported by a project grant
from NICHD (HD 19423-02). |
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