Abstract
There is an ongoing debate whether an impairment of visual attentional functions constitutes an additional or even an isolated deficit of developmental dyslexia (DD). Especially performance in tasks that require the processing of multiple visual elements in parallel has been reported to be impaired in DD. We review studies that used parameter-based assessment for identifying and quantifying impaired aspect(s) of visual attention that underlie this multi-element processing deficit in DD. These studies used the mathematical framework provided by the “theory of visual attention” (Bundesen, 1990) to derive quantitative measures of general attentional resources and attentional weighting aspects on the basis of behavioral performance in whole- and partial-report tasks. Based on parameter estimates in children and adults with DD, the reviewed studies support a slowed perceptual processing speed as an underlying primary deficit in DD. Moreover, a reduction in visual short term memory storage capacity seems to present a modulating component, contributing to difficulties in written language processing. Furthermore, comparing the spatial distributions of attentional weights in children and adults suggests that having limited reading and writing skills might impair the development of a slight leftward bias, that is typical for unimpaired adult readers.
Highlights
VISUAL ATTENTION AND DEVELOPMENTAL DYSLEXIA (DD) Visual attentional functions are currently discussed as being related to developmental dyslexia (DD), a disorder in written language acquisition, that cannot be explained by age, visual sensory problems, or inadequate reading instruction (World Health Organization, 2011)
In both children with DD examined by Dubois et al (2010), visual processing speed was severely reduced compared to controls while visual threshold t0 was normal
The central role of visual processing speed for reading performance seems to go beyond DD pathology: first, in a recent theory of visual attention” (TVA)-based study Lobier et al (2013) showed that, in typically developing children, the individual speed of visual processing predicted that of text reading
Summary
VISUAL ATTENTION AND DEVELOPMENTAL DYSLEXIA (DD) Visual attentional functions are currently discussed as being related to developmental dyslexia (DD), a disorder in written language acquisition, that cannot be explained by age, visual sensory problems, or inadequate reading instruction (World Health Organization, 2011). It is suggested that people with DD have a reduced visual attentional span, assessed as the amount of elements that can be reported from a briefly displayed array (Bosse et al, 2007; Prado et al, 2007; Valdois et al, 2011, 2012; Lobier et al, 2012) This deficit could be caused by an enhanced visual threshold, a reduction in visual processing speed or VSTM storage capacity, or by a combination of such deficits. People with DD might be especially prone to interference (Sperling et al, 2005; Roach and Hogben, 2007; Moores et al, 2011; Stevens et al, 2013) and such susceptibility to distracting information might reduce the amount of relevant elements encoded from briefly displayed multi-element arrays
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