The authors say that studies comparing binocular eye movements during reading and visual search in dyslexic children are inexistent. In the present study they examined ocular motor characteristics in dyslexic children versus two groups of non dyslexic children with chronological/reading age-matched. Binocular eye movements were recorded by an infrared system (mobileEBTH, e(ye)BRAIN) in twelve dyslexic children (mean age 11 years old) and a group of 9 chronological age-matched and 10 reading age-matched non dyslexic children. Two visual tasks were used: text reading and visual search. Infrared devices permit recording eye movements on a graph for further analysis.
Independently of the task, the ocular motor behavior in dyslexic children is similar to those reported in reading age-matched non dyslexic children: many and longer fixations as well as poor quality of binocular coordination during and after the saccades.
Note: If the age reading scores are similar in both groups of children, and one of the group includes dyslexic children, we could assume that the group of children called “normal readers” have not scored very high on the reading task (like the dyslexics). That would explain the behavior of eye movements (ocular motor) of the two groups is similarly ineffective. Difficult to understand?
According to the authors, for the two groups of dyslexic and non dyslexic children, the two tasks (reading and visual search) produced similar effects in terms of fixations and in terms of binocular coordination. It is believed that reduced visual and attentional span (or “visuo-attentional window”) which limits the number of letters that can be processed simultaneously, could have a similar impact on reading and visual search, due to the visuo- attentional demand similar in both tasks. Most likely, at least for these two groups of children for whom reading skills are not yet well structured, reading and visual search has important requirements in the spheres of vision-perception, attention and space processing.
In contrast, chronological age-matched non dyslexic children showed a small number of fixations and short duration of fixations in reading task with respect to visual search task; furthermore their saccades were well yoked in both tasks. The atypical eye movement’s patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an immaturity of the ocular motor saccade and vergence systems interaction.
Recording of eye movements during reading (first column) and visual search (second column). We observe that the number and duration of fixations of the dominant right eye for a dyslexic child (11 years old), a non-dyslexic child 9 years old and a 11 years old non-dyslexic. The dyslexic child shows more fixations and regressions (backward movements). In the second case, the eye movements of the non-dyslexic child of 9 years old are more efficient but still lack precision if we compare the movements of the 11 years old non-dyslexic child.
Source: Bucci MP, Nassibi N, Gerard C-L, Bui-Quoc E, Seassau M (2012) Immaturity of the Oculomotor Saccade and Vergence Interaction in Dyslexic Children: Evidence from a Reading and Visual Search Study. PLoS ONE 7(3): e33458.
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