Differences in eye movements and reading problems in dyslexic and normal children.
Eden GF., Stein JF., Wood HM., Wood FB.
It has been suggested that eye movement abnormalities seen in dyslexics are attributable to their language problems. In order to investigate this claim, we studied eye movements in dyslexic children, during several non-reading tasks. Dyslexic children were compared to normal and backward readers on measures of fixation, vergence amplitude, saccade and smooth pursuit. The results were compared to the children's phonological ability. Dyslexic children (n = 26) had significantly worse eye movement stability during fixation of small targets than normal children (n = 39). Vergence amplitudes were lower for dyslexics than for controls. A qualitative assessment of saccadic eye movements revealed that dyslexics exhibit fixation instability at the end of saccades. Assessment of smooth pursuit revealed poor smooth pursuit in the dyslexic group, particularly when pursuing a target moving from left to right. Dyslexic children also performed significantly worse than normal children on a test of phonological awareness (Pig Latin). Eye movement results were studied in the light of the findings on phonological awareness: dyslexics with small vergence amplitudes also always have poor phonemic awareness. However, poor fixation control is found in dyslexics with or without poor phonological ability. The backward reading children performed similar to the dyslexics on all tests, suggesting that the deficiencies observed in this study are not specific to children with dyslexia. The problems experienced by the children (revealed by a questionnaire) are in agreement with those measured in terms of eye movement recordings and phonemic awareness. Sex, handedness, IQ or the presence of attention deficit disorder (ADD) did not appear to influence the children's performances on any of the eye movement tasks. The presence of oculomotor abnormalities in a non-reading task strongly suggests that the underlying deficit in the control of eye movements seen in dyslexics is not caused by language problems alone.