The need to differentiate the magnocellular system from the dorsal stream in connection with dyslexia

Skottun, Bernt C.

doi:10.1016/j.bandc.2015.01.001

Cited by 19 publications

(11 citation statements)

References 116 publications

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“…Motion coherence thresholds measured using RDKs are correlated with reading rate in school‐aged children; nevertheless, the evidence between impaired motion perception and poorer reading performance is controversial . Impaired biological motion perception has also been linked to social cognition .…”

Section: Cortical Processing Of Visual Informationmentioning

confidence: 99%

The effects of preterm birth on visual development

Leung

Thompson

Black

et al. 2018

Clinical and Experimental Optometry

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Children born very preterm are at a greater risk of abnormal visual and neurological development when compared to children born at full term. Preterm birth is associated with retinopathy of prematurity (a proliferative retinal vascular disease) and can also affect the development of brain structures associated with post‐retinal processing of visual information. Visual deficits common in children born preterm, such as reduced visual acuity, strabismus, abnormal stereopsis and refractive error, are likely to be detected through childhood vision screening programs, ophthalmological follow‐up or optometric care. However, routine screening may not detect other vision problems, such as reduced visual fields, impaired contrast sensitivity and deficits in cortical visual processing, that may occur in children born preterm. For example, visual functions associated with the dorsal visual processing stream, such as global motion perception and visuomotor integration, may be impaired by preterm birth. These impairments can continue into adolescence and adulthood and may contribute to the difficulties in learning (particularly reading and mathematics), attention, behaviour and cognition that some children born preterm experience. Improvements in understanding the mechanisms by which preterm birth affects vision will inform future screening and interventions for children born preterm.

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Section: Cortical Processing Of Visual Informationmentioning

confidence: 99%

The effects of preterm birth on visual development

Leung

Thompson

Black

et al. 2018

Clinical and Experimental Optometry

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“… Sperling et al (2005) pointed out that deficits in noise exclusion, not M processing, contributed to the etiology of dyslexia. Additionally, Skottun (2015) pointed out that CM deficit should be attributed to deficits of dorsal stream rather than M pathway; namely, M pathway and dorsal stream should be distinguished. Although M deficit theory is still debatable, M deficits have been extensively evidenced in DD.…”

Section: Introductionmentioning

confidence: 99%

The effect of magnocellular-based visual-motor intervention on Chinese children with developmental dyslexia

Qian

2015

Front. Psychol.

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Magnocellular (M) deficit theory points out that the core deficit of developmental dyslexia (DD) is the impairment in M pathway, which has been evidenced in many previous studies. Based on the M deficit, some researchers found that visual intervention focusing on M deficit improved dyslexics’ M function as well as reading abilities. However, the number and reliability of these training studies were limited. Therefore, the present study conducted an M-based visual-motor intervention on Chinese children with DD to investigate the relationship between M deficit and Chinese DD. Intervention programs included coherent motion detection, visual search, visual tracking, and juggling, which were related to M function. The results showed that M function and phonological awareness of training dyslexic group were improved to a normal level as age-matched normal children after intervention, while non-training dyslexics did not. It supported M deficit theory, and suggested M deficit might be the core deficit of Chinese DD.

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“…These metacontrast change detection studies showed superior change detection for upper visual field locations. Skottun (2000) rightly points out that the magnocellular pathway and the dorsal cortical stream are different entities (Skottun, 2015), but fails to acknowledge the dominance of magnocellular inputs into early dorsal cortical stream. Logically, this demands the use of physiological techniques to detect where in the brains of those with reading problems, lie the differences in activity from those who read normally.…”

Section: Introductionmentioning

confidence: 99%

Dyslexic children show altered temporal structure of the nonlinear VEP

Rutkowski

Crewther

2019

Preprint

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The neural basis of dyslexia remains unresolved, despite many theories relating dyslexia to dysfunction in visual magnocellular and auditory temporal processing, cerebellar dysfunction, attentional deficits, as well as excessive neural noise. Recent research identifies perceptual speed as a common factor, integrating several of these systems. Optimal perceptual speed invokes transient attention as a necessary component, and change detection in gap paradigm tasks is impaired in those with dyslexia. This research has also identified an overall better change detection for targets presented in the upper compared with lower visual fields. Despite the magnocellular visual pathway being implicated in the aetiology of dyslexia over 30 years ago, objective physiological measures have been lacking. Thus, we employed nonlinear visual evoked potential (VEP) techniques which generate second order kernel terms specific for magno and parvocellular processing as a means to assessing the physiological status of poor readers (PR, n=12) compared with good readers (GR, n=16) selected from children with a mean age of 10yr. The first and second order Wiener kernels using multifocal VEP were recorded from a 4° foveal stimulus patch as well as for upper and lower visual field peripheral arcs. Foveal responses showed little difference between GR and PR for low contrast stimulation, except for the second slice of the second order kernel where lower peak amplitudes were recorded for PR vs GR. At high contrast, there was a trend to smaller first order kernel amplitudes for short latency peaks of the PR vs GR. In addition, there were significant latency differences for the first negativity in the first two slices of the second order kernel. In terms of peripheral stimulation, lower visual field response amplitudes were larger compared with upper visual field responses, for both PR and GR. A trend to larger second/first order ratio for magnocellularly driven responses suggests the possibility of lesser neural efficiency in the periphery for the PR compared with the GR. Stronger lower field peripheral response may relate to better upper visual field change detection performance when target visibility is controlled through flicking masks. In conclusion, early cortical magnocellular processing at low contrast was normal in those with dyslexia, while cortical activity related to parvocellular afferents was reduced. In addition, the study demonstrated a physiological basis for upper versus lower visual field differences related to magnocellular function.

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The need to differentiate the magnocellular system from the dorsal stream in connection with dyslexia

Cited by 19 publications

References 116 publications

The effects of preterm birth on visual development

The effects of preterm birth on visual development

The effect of magnocellular-based visual-motor intervention on Chinese children with developmental dyslexia

Dyslexic children show altered temporal structure of the nonlinear VEP

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