Visuomotor processing and hand force coordination in dyslexic children during a visually guided manipulation task

Visually guided eye movements reduce postural sway in dyslexic children

Dyslexic children present poorer postural control performance than their peers, perhaps due to different patterns of eye movements. It has been shown that guided eye movements decrease magnitude of body sway in young and older adults, but there is no evidence whether the search for visual information that occurs during eye movements affects postural control in dyslexic children. The aim of this study was to examine the use of guided eye movements and its pattern in the performance of postural control of dyslexic children during upright quiet stance. Twelve children with dyslexia (10.8 ± 1.1 years old) and 12 non-dyslexic children (10.4 ± 1.5 years old) participated in this study. All children were instructed to maintain an upright quiet stance for 60 s either fixating on a target (fixation condition) displayed 1 m ahead in the center of a monitor at eye level, or performing eye movements to follow a target displayed on one side of a monitor, then disappearing and reappearing immediately on the opposite side with a frequency of 0.5 Hz (guided condition). Three trials for each condition were registered. Body sway was measured with an IRED (OPTOTRAK) placed on the children's back. Eye movements were tracked using eye-tracking glasses (ETG 2.0 - SMI). Dyslexic children swayed with larger amplitude under both fixation and guided conditions than non-dyslexic children. Both dyslexic and non-dyslexic children reduced postural sway magnitude under the guided compared to the fixation condition. All children were able to modulate eye movement according to the conditions (fixation and guided) and no difference in eye movements was observed between dyslexic and non-dyslexic children. Eye movements are modulated similarly based upon the visual conditions in dyslexic and non-dyslexic children, and dyslexic children are capable of using available visual information during eye movements to improve postural control, though they do not equal the performance of non-dyslexic children. Eye movement patterns seem not to be related to poor performance of postural control in dyslexic children.

Dyslexic children need more robust information to resolve conflicting sensory situations

The study involved investigating dyslexic children's postural control responses when visual and somatosensory cues were separately manipulated. Twenty dyslexic and 19 nondyslexic children performed a trial by standing upright inside a moving room and another by lightly touching a moving bar. Both trials lasted 240 s with the following three different stimulus characteristics: low (pretransition), high (transition), and low amplitude (posttransition). Body sway magnitude and the relationship between the movement of the room/bar surface and body sway were examined. When compared to nondyslexic children, dyslexic children oscillated with higher magnitude in the transition and posttransition under visual and somatosensory manipulation; their sway was more influenced by visual manipulation in the transition and posttransition, and they used higher applied force levels in the somatosensory modality in all conditions. The results suggest that dyslexic children could not efficiently reweight visual cues when compared to nondyslexic children. The same was not observed in the somatosensory cues when dyslexic children reduced the influence of the somatosensory stimulus. The proper use of somatosensory information was related to stronger acquired cues and higher applied forces as observed for dyslexic children. Dyslexic children experience difficulties in dynamically reweighting sensory cues although these types of difficulties are overcome when more informative sensory cues are provided.