Perhaps correlational but not causal: No effect of dyslexic readers’ magnocellular system on their eye movements during reading

• Published in: Neuropsychologia Vol. 44; no. 4; pp. 637 - 648
• Main Authors: Hutzler, Florian, Kronbichler, Martin, Jacobs, Arthur M., Wimmer, Heinz
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2006; Elsevier Science
• Subjects: Adolescent; Attention - physiology; Biological and medical sciences; Brain Mapping; Child; Diagnosis, Differential; Disorders of higher nervous function. Focal brain diseases. Central vestibular syndrome and deafness. Brain stem syndromes; Dominance, Cerebral - physiology; Dyslexia; Dyslexia - diagnosis; Dyslexia - physiopathology; Dyslexia - psychology; Eye movements; Eye Movements - physiology; Fixation, Ocular - physiology; Geniculate Bodies - physiopathology; Humans; Intelligence Tests; Longitudinal Studies; Magnocellular deficit; Male; Medical sciences; Nervous system (semeiology, syndromes); Neurology; Neurons - physiology; Oculomotor Nerve - physiopathology; Pattern Recognition, Visual - physiology; Perceptual Disorders - diagnosis; Perceptual Disorders - physiopathology; Perceptual Disorders - psychology; Phonetics; Psycholinguistics; Reaction Time - physiology; Reading; Saccades - physiology; Semantics; Statistics as Topic; String processing; Verbal Learning - physiology; Visual Pathways - physiopathology; Visual search; Dyslexia; Eye movements; Visual search; String processing; Magnocellular deficit; Human; Nervous system diseases; Reading disorder; Eye movement; Language disorder; Communication disorder; Reading; Magnocellular pathway; Language; Vision; Perception; Neurological disorder; Causality
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2005.06.006

During reading, dyslexic readers exhibit more and longer fixations and a higher percentage of regressions than normal readers. It is still a matter of debate, whether these divergent eye movement patterns of dyslexic readers reflect an underlying problem in word processing or whether they are – as the proponents of the magnocellular deficit hypothesis claim – associated with deficient visual perception that is causal for dyslexia. To overcome problems in the empirical linkage of the magnocellular theory with reading, a string processing task is presented that poses similar demands on visual perception (in terms of letter identification) and oculomotor control as reading does. Two experiments revealed no differences in the eye movement patterns of dyslexic and control readers performing this task. Furthermore, no relationship between the functionality of the participants’ magnocellular system assessed by the coherent motion task and string processing were found. The perceptual and oculomotor demands required during string processing were functionally equivalent to those during reading and the presented consonant strings had similar visual characteristics as reading material. Thus, a strong inference can be drawn: Dyslexic readers do not seem to have difficulties with the accurate perception of letters and the control of their eye movements during reading – their reading difficulties therefore cannot be explained in terms of oculomotor and visuo-perceptual problems.