01 NRDC Dyslexia 1-88 update - Texthelp

Developmental dyslexia in adults: a research review 53
problem occurring in other typologies: an unbridgeable gap between ‘(h) those that are
included in this classification’ and ‘(i) etcetera’ (Borges, 2000). The problem arises even in a
univariate classification; in a multivariate classification, it leads to increasing fractionation
(Van Orden et al., 2001).
Is there a more persuasive way of classifying the observations? Need they be classified at all?
Does it help to conceive of all the relevant distributions of reading-related cognitive skills as
being continuously arrayed in a multidimensional space and not distributed in clusters (Ellis,
1985; Stanovich, 1988)? Does it help to consider the question quantitatively, in order to avoid
‘the inherent connotations of discreteness carried by many natural language terms’
(Stanovich, 1988)? In so far as dyslexia (or ‘reading disability’) is conceptualised as a difficulty
in learning how to decode print, the phonological-core variable-difference model (Stanovich,
1988) not only recognises that phonological difficulties are common to both dyslexic and
‘ordinary’ poor readers but, by conceptualising differences in terms of dimensions, it also
avoids the problems of discreteness and residual or mixed categories in dyslexia subtype
analyses.
Although the phonological-core variable-difference model rests on a dimensional concept, it
is claimed to be compatible with the categorical differences implied by subtypes (Morris et al.,
1998). Nor are subtypes the only outstanding issue. The model proposes that the poor reader
with dyslexia has an impairment localised at the phonological core whereas the ordinary poor
reader has impairments extending into a variety of domains (Stanovich, 1988)—essentially the
same distinction drawn between ‘specific reading retardation’ and general reading
backwardness in the Isle of Wight study (Rutter et al., 1970). If the description ‘specific’ has
any meaning at all, whether applied to ‘reading retardation’, learning difficulty, or dyslexia,
things cannot be otherwise.
However, a concept of specificity is less easy to reconcile with the pattern-of-difficulties
concept of dyslexia, where severe and persistent difficulty in learning to read is but one
characteristic among many (Miles, 1983), or with the finding that shared problems may be
more numerous and diverse than allowed for by the model (Hoskyn & Swanson, 2000). The
concept of specificity is correspondingly difficult to reconcile with some of the items listed in
behavioural checklists for dyslexia screening (see Appendices 5 and 6). It is also difficult to
reconcile with our current understanding of human development (Gottlieb & Halpern, 2002)
and its implications for reading (Stanovich, 1986).
Challenges to the categorical assumption of the phonological deficit theory are addressed by
the multi-dimensional phonological-core, variable-difference model of reading disability.
What does the phonological-core variable-difference model predict?
The phonological-core variable-difference model leads to the prediction that the dyslexic’s
impairment, while more localised, is more severe than that of the ‘ordinary’ poor reader and
that because of its severity it will be more difficult to remediate (Stanovich, 1988). Consistent
with this prediction is a recent finding, described by its authors as ‘new, and perhaps
controversial’ (Rack & Hatcher, 2002), that dyslexics are actually less responsive to
intervention than ordinary poor readers. Controversy? Almost certainly. Novelty? No. There is
undoubtedly a conflict between robust findings that students with cognitive deficits in the
domain of phonology are difficult to remediate (Vellutino et al., 1996), or even treatmentresistant
(Chiappe et al., 2001) and claims that ‘the effects of dyslexia can be largely