Postural control in dyslexic and non-dyslexic children

Abstract

Postural control relies to visual-motion processing (afferent or efferent) and this is thought to be deficient in dyslexics. There is a controversy between clinic and fundamental studies as to the presence of posture abnormalities in dyslexics. To explore further this issue, this study examines posture stability in quite stance in 13 dyslexics (mean age: 13.5 years) and in 13 non-dyslexics (mean age: 13 years). Experiment 1 shows that, similarly to adults and elderly, all children (dyslexics and non-dyslexics), present better stability at near distance (i.e. smaller surface area of the COP, smaller lateral and antero-posterior oscillations). This could be due to reduced angular size of retinal motion signals at far, but also to convergence relaxation. Importantly, the surface area of the COP, lateral and antero-posterior oscillations are significantly higher in dyslexics. Experiment 2 examines posture stability while subjects make active vergence movements between a far and a near target. For many dyslexics, moving the eyes back and forth in depth rather improved postural stability. The only significant difference was that the lateral oscillations were still higher in dyslexics. Experiment 3 uses eye movement recordings (video-oculography) and demonstrates that dyslexics have problems with maintaining stable the angle of vergence for a prolonged period. We conclude that mild postural instability may exist in dyslexics but it could be improved by oculomotor and attention processes.

Postural Control in Nonamblyopic Children with Early-Onset Strabismus

“…Despite the conflict with the physical distance, convergence of the eyes resulted in an improvement in postural stability. This stabilizing effect of proximity is present in children 3 and in the elderly. 2 Bucci et al showed that children with a vergence deficit who suffered from vertigo still presented this stabilizing effect of proximity with respect to postural control even though they were less stable than control children for conditions at near and far distances.…”

“…As mentioned above, Kapoula and Bucci confirmed that for dyslexic children, active vergence eye movements exert a stabilizing effect on posture that has not been observed in non-dyslexic control children. 3 They attributed these results to dyslexic children's greater visual attentional involvement, as well as to the mobilization of attentional resources together with the execution of eye movements. Because dyslexic children also have attentional difficulties, active vergence movements could help to focus their attention by shifting between distal and proximal targets.…”

“…In a recent study dealing with dyslexic and non-dyslexic children, Kapoula and Bucci postulated the existence of an underlying attentional mechanism that is activated by eye movements and that also might contribute to improved postural performance in dyslexics. 3 A similar attentional mechanism, observable only in terms of the variance of speed parameter, also might be at work in strabismic patients, albeit in a more subtle way.…”

“…These results are in line with previous work on non-strabismic children. 3,4 Thus, active vergence movements can be particularly useful for actively maintaining postural stability with less effort. This observation highlights the importance of vergence eye movements, even when deficient.…”

Spherical Lenses and Prisms Lead to Postural Instability in Both Dyslexic and Non Dyslexic Adolescents

“…Kapoula and Bucci [1] measured postural control in 13 year-old dyslexic adolescents during both closed and opened eye conditions while they were instructed to fixate a target at distances of 25 cm and 150 cm. Dyslexics were more unstable during such fixation tasks regardless of the distance at which the target was placed, be it proximal or distal.…”