Abstract
To our knowledge, behavioral studies recording visual fixations abilities in dyslexic children are scarce. The object of this article is to explore further the visual fixation ability in dyslexics compared to chronological age-matched and reading age-matched non-dyslexic children. Fifty-five dyslexic children from 7 to 14 years old, 55 chronological age-matched non-dyslexic children and 55 reading age-matched non-dyslexic children participated to this study. Eye movements from both eyes were recorded horizontally and vertically by a video-oculography system (EyeBrain® T2). The fixation task consisted in fixating a white-filled circle appearing in the center of the screen for 30 s. Results showed that dyslexic children produced a significantly higher number of unwanted saccades than both groups of non-dyslexic children. Moreover, the number of unwanted saccades significantly decreased with age in both groups of non-dyslexic children, but not in dyslexics. Furthermore, dyslexics made more saccades during the last 15 s of fixation period with respect to both groups of non-dyslexic children. Such poor visual fixation capability in dyslexic children could be due to impaired attention abilities, as well as to an immaturity of the cortical areas controlling the fixation system.
Highlights
Visual fixation consists in maintaining an image on the fovea in order to perceive it. Palvidis (1981) was the first to report poor fixation capabilities in 12 dyslexic children with respect to 12 non dyslexic children
We found an interaction between groups of children and period of fixation showing that dyslexic children made more saccades during the final half of the task than during the initial half (p < 0.0001)—in the other two groups this was not the case
Our finding suggests that dyslexic children could have a weak ability to suppress unwanted saccades, most likely due to their difficulty in inhibition processing as well as to attentional deficits, even if we excluded in this study dyslexic with attentional deficiencies
Summary
Visual fixation consists in maintaining an image on the fovea in order to perceive it. Palvidis (1981) was the first to report poor fixation capabilities in 12 dyslexic children with respect to 12 non dyslexic children. De Luca et al (1999) explored fixation capability in dyslexic children and in non-dyslexic children of comparable chronological age and they did not find any difference between the two groups of children. We explored further fixation capability in a large number of dyslexic children and we compared their results with those of two groups of non-dyslexic children having similar chronological and reading age. In 1995, the same authors explored further the role of SC cells in monkeys and they confirmed that some cells in the rostral pole are responsible for visual fixation while the other cells are responsible for preparation and generation of saccades (Munoz and Wurtz, 1995)
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