The Role of Visual Factors in Dyslexia

Abstract

What are the causes of dyslexia? Decades of research reflect a determined search for a single cause where a common assumption is that dyslexia is a consequence of problems with converting phonological information into lexical codes. But reading is a highly complex activity requiring many well-functioning mechanisms, and several different visual problems have been documented in dyslexic readers. We critically review evidence from various sources for the role of visual factors in dyslexia, from magnocellular dysfunction through accounts based on abnormal eye movements and attentional processing, to recent proposals that problems with high-level vision contribute to dyslexia. We believe that the role of visual problems in dyslexia has been underestimated in the literature, to the detriment of the understanding and treatment of the disorder. We propose that rather than focusing on a single core cause, the role of visual factors in dyslexia fits well with risk and resilience models that assume that several variables interact throughout prenatal and postnatal development to either promote or hinder efficient reading.

Neurocognitive mechanisms of co‐occurring math difficulties in dyslexia: Differences in executive function and visuospatial processing

“…Individuals with RD demonstrate differences throughout the reading system, including left inferior frontal, occipitotemporal, and temporoparietal brain regions (Kronbichler & Kronbichler, 2018;Martinez-Lincoln et al, 2023;Pugh, 2001;Richlan, 2012;van der Mark et al, 2011). RD is also frequently linked to difficulties with rapid automatized naming (RAN) and executive functioning (Al Dahhan et al, 2022;Daucourt et al, 2020;Lonergan et al, 2019), as well as perceptual differences (e.g., in visual processing and visuospatial attention; see Kristjánsson & Sigurdardóttir, 2023 for a review).…”

“…This discovery is aligned with prior evidence suggesting visual processing differences in both RD and MD. Visual processing deficits also often arise as a possible correlate within multifactorial theories of RD, as multiple aspects of vision (i.e., motion processing, visual attention, high-level visual discrimination, as well as neurocognitive and neuroanatomical differences in the ventral visual stream) have been linked to reading difficulties (Kristjánsson & Sigurdardóttir, 2023). Visuospatial skills in children with RD, such as recalling and reproducing complex figures, may also discriminate between those with and without cooccurring math difficulties (Helland & Asbjørnsen, 2003).…”

Children with dyslexia show no deficit in exogenous spatial attention but show differences in visual encoding

“…There is long-standing controversy about the visual factors associated with dyslexia (Kristjansson & Sigurdardottir, 2023.;Stein & Kapoula, 2012). Of all the measures of sensory processing that have been studied in relation to dyslexia, the multi-letter processing task has the strongest evidence for identifying a subgroup of struggling readers who are not captured by conventional measures of phonological processing (Valdois et al, 2021).…”

Non-Linguistic Working Memory Challenges in Dyslexia in The Context of Applied Consumer Psychology

“…Research on the specific learning disorder dyslexia (Lyon et al, 2003) predominantly uses linguistic stimuli or tasks, as the most prominent theories used to postulate a failure in phonological awareness (Snowling, 1980(Snowling, , 1981) -a linguistic process. Competing theories focus on deficits in non-linguistic processes, such as perceptual sensory processing (Kristjánsson & Sigurdardottir, 2023;Stein & Walsh, 1997) or general visual attention (Vidyasagar & Pammer, 2010). However, recent advances favour a multifactorial model that underlies dyslexia-related deficits (O'Brien & Yeatman, 2021).…”

“…However, the specific role of visuo-spatial working memory in relation to behavioural performance of individuals with dyslexia remains elusive due to several studies reporting contradictory findings using non-linguistic tasks (de Carvalho et al, 2014;Vellutino, 1979). Dyslexia involves cognitive challenges beyond reading, yet the role of visual factors in contributing to these challenges has often been underestimated in the literature, impeding our ability to understand and effectively treat the disorder (Kristjánsson & Sigurdardottir, 2023). To Gagné et al…”