01 NRDC Dyslexia 1-88 update - Texthelp

Developmental dyslexia in adults: a research review 51
While this finding does not invalidate the phonological deficit hypothesis as a description of
what for many practitioners and researchers is the central aspect of dyslexia, it offers no
support for the phonological deficit hypothesis as an explanation of dyslexia.
Most, but not all studies, have failed to obtain evidence of reduced or absent spelling-tosound
regularity effects in dyslexia. This has been the case irrespective of whether dyslexia is
defined by discrepancy or by low-end cut off scores. In other words, the overwhelming
majority of spelling evidence appears not to support the prediction of the phonological deficit
model (Metsala & Brown, 1998; Metsala et al., 1998). If the model were correct, dyslexic
people would only be able to read by recognising the shapes of words (rather than the letter
sequences they are composed of) and so there would be no difference in their ability to read
regular and exception words. Since differences in the ability to read regular and exception
words are reported in both dyslexics and reading age controls, this evidence appears not to
support the phonological deficit model (Ellis et al., 1997a).
The phonological deficit theory does not explain problems with motor skill development.
The phonological deficit theory is challenged as an explanation (as opposed to a description)
of dyslexia by the difficulty of distinguishing dyslexics and non-dyslexic people in terms of
their spelling errors and their abilities to read regular and exception words.
Do phonological deficits differentiate ‘dyslexics’ from other poor readers?
With respect to spelling and handwriting, the phonological deficit theory of dyslexia is too
narrow; with respect to reading, it is too broad. Implicit in the foregoing sections is the
question of whether measures of phonological awareness can differentiate dyslexic people
from ‘ordinary’ poor readers. It is a matter of definition that pseudoword repetition and other
phonological measures differentiate poor readers from good readers. However, do they
differentiate developmental dyslexic people from ‘ordinary’ poor readers? As an example, the
task of pseudoword repetition requires accurate speech perception, efficient verbal working
memory and the ability to keep phonological representations distinct (Holopainen et al., 2001).
Task performance can be compromised by deficits in speech perception (Chiappe et al., 2001);
in children with mild-to-moderate sensorineural hearing loss, serious difficulty with
pseudoword repetition has been found to be compatible with normal literacy ability (Briscoe
et al., 2001). Task performance can also be affected by vocabulary knowledge (Dollaghan et
al., 1995), which is in its turn affected by knowledge gained from exposure to print.
Otherwise-unimpaired adults who never had the opportunity to learn to read have been shown
to experience difficulty in repeating pseudowords (Castro-Caldas et al., 1998).
In the light of these and other findings (e.g. Bishop, 2001), it appears that the pseudoword
repetition task does not differentiate between those with dyslexia and ordinary poor readers,
possibly because it assesses what is common to both groups, namely limitations in
declarative knowledge that might normally have been acquired at home or at school
(Thompson & Johnston, 2000).
It is also possible that the pseudoword repetition task might confound phonological
awareness with general intellectual ability. Although children whose later reading ability was
not discrepant with their assessed intelligence had performed less well at pseudoword
repetition than those who were later considered to be ‘normal’ readers, children whose later
reading difficulties were discrepant with their general ability could not be distinguished from