01 NRDC Dyslexia 1-88 update - Texthelp

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Research Report
& Nicolson, 1991), ‘sluggish attentional shifting’ (Renvall & Hari, 2002), or timing impairments
in speech perception (Goswami et al., 2002; Helenius et al., 2002; Wolff, 2002).
The magnocellular deficit hypothesis itself may be a stage in progress towards a persuasive
biological explanation of those cases of reading difficulty, possibly a minority, associated with
multi-sensory perceptual deficits (Amitay et al., 2002). The hypothesis may not be best
supported by findings from contrast sensitivity studies (Gross-Glenn et al., 1995; Skottun,
2000a, 2000b; Skottun & Parke, 1999). Alternatively, it may be that the information-processing
deficit needs to be reconceptualised as an attentional rather than as a perceptual problem
(Hari & Renvall, 2001; Hayduk et al., 1996; Saarelma et al., 2002; Stuart et al., 2001;
Vidyasagar, 2001). Our present state of knowledge may not permit greater certainty than this.
Although the magnocellular deficit hypothesis drives an active and wide-ranging research
programme, it is too soon to expect any impact on practice in adult literacy teaching.
To conclude this Section, Table 1 summarises very briefly areas of difficulty that are or are not
covered by four of the major theories discussed above.
Table 1. Four theories of dyslexia and their explanatory compass
Reading
Beyond reading
Accuracy Fluency Cognition Movement
Phonological deficit
•
Double deficit • •
Cerebellar deficit • • •
Temporal Processing deficit • • •