01 NRDC Dyslexia 1-88 update - Texthelp

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Research Report
Part two
Explanatory theories of Dyslexia
Caveat 1 ‘The history of dyslexia research, the well-known heterogeneity of dyslexic
children and the very complexity of the reading process argue against any single
unifying explanation for reading breakdown’ (page 432). Wolf, M. and Bowers, P. G.
(1999). The double-deficit hypothesis for the developmental dyslexias. Journal of
Educational Psychology, 91(3), 415–438.
Caveat 2 ‘A difficulty in learning to read, or dyslexia, should not be viewed as a
condition in itself, but as a symptom of a breakdown in one or more of the various
processes involved’ (page 460). Farmer, M. E. and Klein, R. M. (1995). The evidence for
a temporal processing deficit linked to dyslexia: a review. Psychonomic Bulletin &
Review, 2(4), 460–493.
Caveat 3 ‘Some of the seeming confusion in the study of dyslexia may simply reflect
the fact that complex systems may break down in complex ways’ (page 260).
Seidenberg, M. S. (1992). Dyslexia in a computational model of word recognition in
reading. In P. B. Gough & L. C. Ehri & R. Treiman (Eds.), Reading Acquisition.
Hillsdale, NJ: Laurence Erlbaum Associates.
Introduction
The theories reviewed here are attempts to describe what is going wrong for people who have
difficulty in learning to read and write and to explain why it is going wrong for them. Not all of
the theories attempt both tasks. Nevertheless, the different kinds of theory can be fitted into
an inclusive causal model entailing three levels of analysis, one of which is descriptive, one of
which is explanatory at the proximal level and one of which is explanatory at the distal level—
behavioural, cognitive and biological explanations. The original model was developed at the
Medical Research Council’s former Cognitive Development Unit (Morton & Frith, 1995) at
about the same time that the comparable biobehavioural systems model was proposed in the
USA (Fletcher et al., 1995). It has been adopted in accounts of dyslexia in adults (Lee, 2000,
2002) and its usefulness as an explanatory framework is widely acknowledged (Nicolson et
al., 2001a; Richards et al., 2002; Snowling, 2000). It has recently been elaborated in a general
model of reading and the influences on reading development (Jackson & Coltheart, 2001). In
this form (see Appendix 4), it offers useful points of reference for the present review.
Reading, as most dyslexia theorists use the term, refers to the decoding of single words, but
this is only one stage in the acquisition of literacy. A more elaborate account describes
reading as a cognitive activity accomplished by a mental information-processing system made
up of a number of distinct processing subsystems or component skills (Carr et al., 1990),
where the input is print and the processes applied to the input yield output in the form of
word meaning, syntactic representations of sequences of words and pronunciations (Jackson
& Coltheart, 2001). This is not to suppose that anyone believes the ability to recognise and
pronounce words—‘word calling’, or ‘barking at print’—is the final aim of reading instruction;
if the basic skill is to derive meaning from print, then reasoning and discourse are ultimately
what make literacy functional (Rayner et al., 2001). That being so, it may help to follow the