Visual attention span capacity in developmental dyslexia: A meta-analysis

The visual attention span (VAS) deficit theory of developmental dyslexia (DD) indicates that impaired VAS may cause reading disabilities. However, whether people with dyslexia have VAS deficit is still controversial. The current review evaluates the literature regarding the relationship between VAS and poor reading, as it also examines the possible moderators in measuring the VAS capacity of individuals with dyslexia. A total of 25 papers, with participants of 859 readers with dyslexia and 1048 typically developing readers were included in the meta-analysis. The sample sizes, means and standard deviations (SDs) of the scores in VAS tasks were extracted separately from the two groups, which were used to calculate the effect sizes of group differences in SDs and means by the robust variance estimation model. Results showed higher SDs and lower averages of the VAS test scores for readers with dyslexia than those for typically developing readers, revealing high individual variability and remarkable deficits in VAS of DD. Further subgroup analyses showed that the characteristics of VAS tasks, background languages, and participants modulated the group differences in VAS capacities. Particularly, the partial report task with symbols of relatively high visual complexity and key pressing may be the optimal measurement of VAS skills. A greater VAS deficit in DD was observed in more opaque languages, with a trend of developmental increase in attention deficit, especially at the primary school level. Moreover, this VAS deficit seemed to be independent of the phonological deficit of dyslexia. These findings to some extent supported the VAS deficit theory of DD and (partially) explained the controversial relationship between VAS impairment and reading disabilities.