01 NRDC Dyslexia 1-88 update - Texthelp

Developmental dyslexia in adults: a research review 17
How can dyslexia be defined?
This section sets out a range of theoretical possibilities. Answers to the practical question
‘Who do we describe as ‘dyslexic’?’ will be reviewed in the next section.
The pathway of possibility divides at the start of the journey. The word ‘dyslexia’ might
represent either a natural kind, that is, part of the reality of the world that we perceive
directly; or it might represent a construct, an idea that people have developed to help them
theorise about the workings of the world—in short, a tool for thinking with. Constructs
themselves are neither true nor false. Instead, they are useful or otherwise, depending on our
purpose. What is useful for research might not be useful for intervention and vice versa.
If ‘dyslexia’ is a construct, rather than a natural kind, our path divides again. The construct of
‘dyslexia’ might derive from a single behavioural feature, or it might derive from a set of
behavioural features. If ‘dyslexia’ derives from a set of behavioural features, the path divides
once more. Either ‘dyslexia’ derives from a set of behavioural features, or ‘signs’, all of which
are both necessary and sufficient for identifying a person as ‘dyslexic’, or it derives from a set
of behavioural features, none of which is necessary or sufficient by itself, although a specified
number of those features might be sufficient for identifying a person as ‘dyslexic’ (Bailey,
1973). The definitions collected in Appendix 1 and the analysis in Appendix 2, suggest that
there is a ‘dyslexia’ in every one of these possible categories.
Dyslexia can be defined in more ways than one, but each definition outlines a different
concept.
Who do we describe as ‘dyslexic’?
Not surprisingly, then, there is no consensus as to who might be described as ‘dyslexic’.
■
■
■
■
■
■
■
Either people are ‘dyslexic’ if they have alphabetic skills deficits (Seymour, 1986; Stanovich,
1996).
Or people are ‘dyslexic’ if they have severe and persistent difficulty in acquiring alphabetic
skills, even though their difficulties might be attributable to moderate learning difficulties or
sensory impairments (British Psychological Society, 1999).
Or people are ‘dyslexic’ if they experience difficulty in attaining fluency by automatising wordrecognition
skills, so long as that difficulty can be attributed, at least in part, to a
constitutional factor (Gersons-Wolfensberger & Ruijssenaars, 1997).
Or people are ‘dyslexic’ if their difficulty in acquiring alphabetic skills cannot be attributed to
any more probable explanation (such as moderate learning disability or sensory impairment),
especially if that explanation relates to experience or opportunity; and this definition is
‘exclusionary’ (World Federation of Neurology, 1968).
Or, with a difference of emphasis, people are ‘dyslexic’ if their difficulty in acquiring
alphabetic skills is accompanied by specific neurological impairments, no one of which may
be necessary or sufficient for diagnosis; and this definition is ‘inclusionary’ (Miles, 1982).
Or people are ‘dyslexic’ if they show a characteristically uneven pattern of facility and
difficulty; this definition, too, is inclusionary (Miles, 1983).
Or people are ‘dyslexic’ if they share a secondary characteristic with others who have
difficulty in acquiring alphabetic skills, even if they do not experience this difficulty
themselves (Miles, Wheeler, & Haslum, 2003).
The various possible answers to the question ‘Who do we describe as ‘dyslexic’?’ imply, in