01 NRDC Dyslexia 1-88 update - Texthelp

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Research Report
Separate concurrent and predictive correlates have been found for tests of rapid automatised
naming and tests of phonological segmentation and decoding (Meyer et al., 1998), providing
support for the double-deficit hypothesis. Moreover, particular emphases on both processing
speed and the integration of an ensemble of lower level, visual-perceptual processes with
higher-level cognitive and linguistic subprocesses may distinguish naming speed from
phonological processing (Wolf & Bowers, 1999).
Because rapid naming has predictive power only for poor readers, not for average readers, it
might be that impaired readers are qualitatively different from the normal-reading population
and are not simply the ‘tail’ of a normal distribution of reading ability (Meyer et al., 1998).
The double-deficit hypothesis is supported by the finding that measures of accuracy and
fluency have separate correlates.
Cognitive components of rapid naming
Naming speed has been conceptualised as ‘a complex ensemble of attentional, perceptual,
conceptual, memory, phonological, semantic and motoric subprocesses that place heavy
emphasis on precise timing requirements within each component and across all components’
(Wolf et al., 2000a). In a more detailed formulation, the components include: attention to
stimulus; bihemispheric visual processes responsible for initial feature detection, visual
discrimination and pattern identification; integration of visual feature and pattern
identification with stored orthographic representations; integration of visual information with
stored phonological representations; access and retrieval of phonological labels; activation
and integration of semantic and conceptual information; and motoric activation leading to
articulation (Wolf & Bowers, 1999). However, not all of the constructs have a precise
definition, nor are the components of rapid naming tasks measured directly (Pennington et
al., 2001). This is not to claim that they cannot be defined or that they cannot be measured.
However, it is a reminder that the double-deficit hypothesis remains, pending further
research, a hypothesis. It is not a dogma.
Reading fluency is a complex process and further research is needed for these complexities
to be better understood.
What causes the naming-speed deficit?
Slow naming speed persists as a characteristic of severely disabled readers (Bowers & Wolf,
1993). Automaticity of retrieval, not knowledge of names itself (as in confrontational naming
tasks), appears to give rapid automatised naming its predictive power (Meyer et al., 1998). But
is it then a marker of lexical encoding processes (Ellis & Miles, 1981), reflecting the precise
timing mechanisms necessary to the development of orthographic codes and to their
integration with phonological codes (Bowers & Wolf, 1993)? Do naming-speed deficits reflect
a larger, systemic timing deficit (Wolf et al., 2000a)? These questions entail ‘two highly
complex and unresolved issues’: whether naming speed represents the linguistic analogue of
a larger, potentially domain-general timing deficit that goes beyond language and how such a
broadened conceptualisation of processing-speed deficits would relate to reading processes
(Wolf et al., 2000a).
When the hypothesis was first proposed, it was thought that slow naming speed could be
predictive of reading difficulty by several interrelated routes: as an index of inefficient