Reading
Do kids with dyslexia or ADHD have visual processing problems?
Open access · cc by · source: Europe PMC
Children with reading disorder struggled specifically with remembering the order of visual shapes, not with seeing or remembering single shapes, and this order memory modestly predicted reading skill.
Study at a glance
- Design
- Cross-sectional — Diagnostic-group comparison (MANCOVA controlling verbal IQ) on three visual perceptual subtests, plus hierarchical regressions predicting basic reading in the whole sample.
- N
- N=264 · 264 children: 51 with reading disorder, 88 with ADHD, 51 with both, and 74 typically developing controls.
- Population
- Community sample of children aged 8-12 in the United States
- Outcome
- Visual discrimination, visual memory for single figures, and visual sequential memory scores; basic reading (word reading and nonword decoding)
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Key findings
Children with reading disorder alone matched controls on visual discrimination and on memory for single figures, and children with ADHD alone matched controls on all three tests. Both groups with reading disorder did worse than controls on memory for shape sequences, whereas the ADHD-only group did not. The comorbid group was weaker on all three tests, which the authors linked to their greater attention problems rather than a separate visual deficit. Visual sequential memory was the only visual skill that predicted basic reading, adding only about 2 to 3% of explained variance beyond verbal IQ and phonological or orthographic skill.
Methodology
The researchers tested 264 children aged 8 to 12 from the community: 51 with a reading disorder, 88 with ADHD, 51 with both conditions, and 74 typically developing controls. Each child completed three untimed visual tests: matching complex figures (discrimination), recognising a single complex figure from memory, and recognising the correct order of a sequence of simple shapes. Groups were compared while controlling for verbal IQ, and regressions tested whether visual skills predicted basic reading after accounting for verbal IQ and either phonological awareness or spelling-pattern (orthographic) knowledge.
Limitations
The sample came from the community and had relatively mild reading disorder and ADHD, so clinic samples might show larger or broader deficits. Only three subtests from one test battery were used, and the sequence task used easily named shapes, so it cannot separate a pure memory-for-order problem from weaker verbal labelling. The design is correlational and measured at one time point, so it cannot show that poor sequential memory causes reading difficulty. The attention explanation for the comorbid group rests on follow-up correlations rather than a direct test.
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