1.2.2 The ‘Visual deficit’ hypotheses

In the early 1900s, Samuel Orton coined ‘strephosymbolia’ (derived from Ancient Greek, roughly meaning ‘twisted symbols’) to describe children with reading difficulties who reversed letters; this could involve the confusing of letters such as ‘b’ and ‘d’, or mixing up their positions within a word, e.g. writing ‘was’ as ‘saw’.

From these and other observations, he suggested that their reading difficulties might reflect some kind of visual processing impairment involving incomplete specialisation between the left and right sides of the brain.

You may recall from Week 1 that dyslexia was once called ‘word blindness’, focusing on visual-perceptual issues. Early research sought perceptual factors, but by the 1970s, the phonological deficit model became dominant, linking reading difficulties to language processing. Recently, interest in visual deficits has resurfaced, suggesting they may also play a role (Everatt, Bradshaw and Hibbard, 1999; Whiteley and Smith, 2001; Sigurdardottir, Ólafsdóttir and Devillez, 2021; Stein, 2022). Seymour (1986) highlighted that written language relies on visual systems, and some dyslexic individuals show visual processing weaknesses independent of phonological issues.

It’s important to recognise that visual and phonological problems aren’t mutually exclusive, and dyslexia varies among individuals. Biological and environmental interactions mean the same issue can lead to different outcomes.