It is the egg, not the chicken; dorsal visual deficits present in dyslexia are not present in illiterate adults

Abstract

Some individuals with dyslexia demonstrate deficits in reading, visual attention, and visual processing which can be attributed to a functional failure of the magnocells in the visual system or in the dorsal visual pathway. The study examines the role of magno/dorsal function in dyslexic adults compared with normal, illiterate, and semi‐literate readers. Coherent motion and coherent form were used in Experiment 1, and the frequency doubling illusion and static‐gratings were used in Experiment 2. If a magno/dorsal deficit is demonstrated for dyslexic readers but not illiterate, semi‐literate, and normal reading adults, then the deficit cannot be attributed to reading experience. Illiterate adults performed the same as normal and semi‐literate readers in coherent motion and frequency doubling tasks, and all three groups performed better than the dyslexic readers. There was no difference between any of the groups in the coherent form or static grating tasks. Together, these studies show that illiterate and semi‐literate adults do not demonstrate a magno/dorsal deficit that is a characteristic of some sufferers of dyslexia. Therefore, magno/dorsal deficits in dyslexia are unlikely to be a consequence of failing to learn to read but rather provides evidence to suggest a causal role for reduced visual magno/dorsal processing.

Association between auditory temporal and visual processing in reading skill

“…Pammer and Wheatley 14 verified that a group of 21 dyslexics had a poorer performance in detecting a visual stimulus selective of the magnocellular system, when compared to 19 readers of the control group (F (1.38) = 13.6, p< 0.001), with diminished sensibility in comparison with the standardized age cohort. In the study by Flint and Pammer 12 , illiterate adults obtained the same performance as that of normal and semi-illiterate readers in temporal and spatial tasks specific of the visual magnocellular system, and these three groups had a better performance than the group of dyslexic readers. The authors conclude 12 that this functional failure of the dorsal visual pathway in dyslexia is probably not a consequence of the lack of reading; they point to a causal role of the magnocellular processing, instead.…”

A Temporal Sampling Basis for Visual Processing in Developmental Dyslexia

“…Pre-readers at risk of dyslexia show the same threshold differences to the FD illusion presented at 50 Hz ( Kevan and Pammer, 2008 ) and illiterate, semi-literate, and literate adults are all equally sensitive to the illusion presented at 50 Hz ( Flint and Pammer, 2011 ). This suggests that sensitivity to the FD illusion is not dependant on magnocellular development as a child learns to read and is therefore not a consequence of failing to learn to read ( Kevan and Pammer, 2008 ; Flint and Pammer, 2019 ). Furthermore, individual differences in sensitivity to the FD illusion are predictive of reading performance in dyslexic children ( Gori et al, 2014 ).…”

Predicting early reading fluency based on preschool measures of low‐level visual temporal processing: A possible mediation by high‐level visual temporal processing skills

“…Previous research has usually adopted tasks of gap detection, temporal order judgement, coherent motion detection, and moving/flickering grating detection to measure low‐level visual temporal ability (Farmer & Klein, 1995; Flint & Pammer, 2018; McLean et al, 2011). Relevant studies in the contexts of different languages have found that children's performances in coherent motion detection, temporal order judgement, and moving grating detection were significantly correlated with word/sentence reading speed (Kevan & Pammer, 2008; Lawton, 2016; Lawton & Shelley‐Tremblay, 2017; Main et al, 2014; Van Zuijen et al, 2012; Zhao, Bi, & Coltheart, 2017).…”

“…Relevant studies in the contexts of different languages have found that children's performances in coherent motion detection, temporal order judgement, and moving grating detection were significantly correlated with word/sentence reading speed (Kevan & Pammer, 2008; Lawton, 2016; Lawton & Shelley‐Tremblay, 2017; Main et al, 2014; Van Zuijen et al, 2012; Zhao, Bi, & Coltheart, 2017). Additionally, relevant studies showed that individuals with reading fluency difficulty had poorer behavioural performance in visual tasks of gap detection (Farmer & Klein, 1995), temporal order judgement (Farmer & Klein, 1995), and coherent motion detection (Conlon, Sanders, & Wright, 2009; Flint & Pammer, 2018; Meng, Cheng‐Lai, Zeng, Stein, & Zhou, 2011; Wright & Conlon, 2009) compared to age‐matched normal readers, revealing dysfunction in VTP for individuals with reading dysfluency. The above findings from group comparisons also revealed a close relationship between low‐level VTP skills and reading fluency (Lobier, Dubois, & Valdois, 2013; Lobier, Zoubrinetzky, & Valdois, 2012; Main et al, 2014; McLean et al, 2011).…”