Vestibular Functioning in Children with Neurodevelopmental Disorders Using the Functional Head Impulse Test.

Several studies in children with neurodevelopmental disorders (NDDs) including autism spectrum disorders (ASDs), reading impairment, or attention deficit/hyperactive disorder (ADHD) pointed toward a potential dysfunction of the vestibular system, specifically in its complex relationship with the cerebellum. The aim of the present study was to test the functional vestibulo-ocular reflex (VOR) responses in children with NDDs to measure functional performance of the vestibular system. The VOR is specifically involved in this stabilization of the image on the retina during rapid movements of the head. To perform this study, four groups of children with ASD, ADHD, reading impairment, and with neurotypical development (TD) were enrolled (n = 80). We performed the functional head impulse test (fHIT), which measured the percentage of correct responses by asking the child to identify an optotype briefly presented during passive head impulse in each direction of each semicircular canal plane. We observed significantly lower correct answers in children with NDDs compared with those with TD (p < 0.0001). Surprisingly, there was no significant difference between the three groups of children with NDDs. Our study fostered preliminary evidence suggesting altered efficiency of vestibular system in children with NDDs. VOR abnormalities estimated using the fHIT could be used as a proxy of NDD impairments in children, and represent a potential biomarker.

Visual Attentional Training Improves Reading Capabilities in Children with Dyslexia: An Eye Tracker Study During a Reading Task.

Dyslexia is a specific disorder in reading abilities. The aim of this study was to explore whether a short visual attentional training could improve reading capabilities in children with reading disorders by changing their oculomotor characteristics. Two groups (G1 and G2) of 25 children with reading disabilities and who are matched in IQ (intelligence quotient), sex, and age participated in the study. The allocation of a subject to a specific group (G1 = experimental group; G2 = control group) was generated in an unpredictable random sequence. The reading task was recorded twice for G1, i.e., before (T1) and after (T2) 10 min of visual attentional training. Training consisted of oculomotor tasks (saccades and pursuits movements) and searching tasks (three different exercises). For G2, the two reading tasks at T1 and T2 were done at an interval of 10 min instead. We found that at T1, oculomotor performances during reading were statistically similar for both groups of children with reading disabilities (G1 and G2). At T2, the group G1 only improved oculomotor capabilities significantly during reading; in particular, children read faster, and their fixation time was shortest. We conclude that short visual attentional training could improve the cortical mechanisms responsible for attention and reading capabilities. Further studies on a larger number of dyslexic children will be necessary in order to explore the effects of different training types on the visual attentional span given its important role on the orienting and focusing visuospatial attention and on the oculomotor performance in children with dyslexia.

Pursuit eye movements in dyslexic children: evidence for an immaturity of brain oculomotor structures?

Background: Dyslexia is a disorder found in 5-10% of school-aged children. Several studies reported visual deficits and oculomotor abnormalities in dyslexic children. The objective of our study was to examine horizontal pursuit performance in dyslexic children, despite its poor involvement in reading. Methods: Eye movements were recorded by video-oculography in 92 children (46 dyslexic children, mean age: 9.77 ± 0.26 and 46 non dyslexic, IQ- and age-matched children). Both the number of catch-up saccades occurring during pursuit task and the gain of pursuit were measured. Results: Catch-up saccades were significantly more frequent in the dyslexic group than in the non-dyslexic group of children. Pursuit performance (in terms of the number of catch-up saccades and gain) significantly improved with increasing age in the non-dyslexic children group only. Conclusions: The atypical pursuit patterns observed in dyslexic children suggest a deficiency in the visual attentional processing and an immaturity of brain structures responsible for pursuit triggering. This finding needs to be validated by neuroimaging studies on dyslexia population.

Impact of Somatosensory Input Deficiency on Subjective Visual Vertical Perception in Children With Reading Disorders.

Purpose: Preliminary evidence indicated that children with a reading disorder (RD) may have deviance in their ability to perform high demanding cognitive tasks, such as reading, depending on somatosensory inputs. Until now, only anecdotical reports suggested that improving somatosensory inputs may influence their ability to maintain a stable perception of the visual world despite continuous movements of our eyes, head, and body. Here, we investigated whether changes in upright perception, the subjective visual vertical (SVV), were modulated by somatosensory inputs in a group of children with RD. Method: The SVV task was used under two distinct conditions, i.e., with or without somatosensory inputs from the foot. We enrolled a group of 20 children with reading disorders and 20 sex-, age-, IQ- matched children with neurotypical development. Results: Responses to the SVV task were found to be significantly less accurate in children with RD than in children with neurotypical development (p < 0.001). In the latter, SVV response did not depend on somatosensory inputs from the foot. In contrast, in children with RD somatosensory inputs, either improved or worsen their SVV depending on the tilt direction (p < 0.01). Conclusion: Our results suggested that SVV responses in children with RD could be related to an immaturity for heteromodal sensory integration, including somatosensory inputs.

Effect of different font sizes and of spaces between words on eye movement performance: An eye tracker study in dyslexic and non-dyslexic children.

The aim of the present study was to explore the possible change in eye movement performance in a group of dyslexic and non-dyslexic children reading four lines of a text with different font sizes and spaces between the words. Fifteen dyslexic children from 7 to 12 years old and two groups of fifteen non-dyslexic children, respectively reading and chronological age-matched group, participated in this study. Horizontal eye movements from both eyes were recorded by a video-system (EyeBrain T2®) while the children were reading a text. Three different texts were used with different font sizes and spaces between words. Results showed that increasing font size and character spacing significantly reduced duration of the fixation and increased the number and amplitude of prosaccades in all groups of children tested. Interestingly, while reading texts in which the letters were larger and more spaced (Texts 2 and 3), the duration of fixations in dyslexic and in non-dyslexic children groups decreased, becoming similar to those reported in the non-dyslexic children group. We suggest that large letter spacing between words could be employed in schools to help dyslexic children in order to ameliorate their reading performance.

Eye movement and postural sway in dyslexic children during sitting and standing.

In this study, we investigated the eye movement and postural control performance in dyslexic children while reading text and performing Landolt reading when sitting and standing. Fifteen dyslexic and 15 non-dyslexic children were asked to sit in a chair while the eye movements were recorded, and were then asked to stand on an unstable platform while eye movements and postural sway were recorded simultaneously at the time of Landolt reading and text reading. Eye movements were recorded binocularly by Mobile EyeBrain Tracker (MobileT2®, SuriCog) and center of pressure excursions were recorded by Multitest Equilibre (by Framiral®). The dependent variables for visual performance in the reading tasks were: total reading time, mean duration of fixation, number of pro- and retro-saccades, and amplitude of pro-saccades. The dependent variable for postural performance was the center of pressure area. The results showed that dyslexic children spent more time reading the text compared to non-dyslexic children (p < 0.02). However, no difference was observed for the Landolt reading task (p > 0.05). Dyslexic children performed longer fixations in the sitting condition as compared to the standing (p < 0.03), namely, higher number of pro- (p < 0.001) and retro- saccades (p < 0.001), and smaller pro-saccades amplitude (p < 0.001). Therefore, when the linguistic and semantic requirements are not involved in the reading task, dyslexic children perform similar to non-dyslexic children even in different task requirements (p > 0.05). Finally, postural performance was poorer in dyslexic children than in non-dyslexic children in both the reading tasks (p < 0.02). However, postural control performance, which was poor in dyslexic children, is not related to lexical and semantic reading requirements.

Developmental Eye Movement test and dyslexic children: A pilot study with eye movement recordings.

The goal of this study is to explore eye movement recordings during the Developmental Eye Movement (DEM) test in dyslexic and non-dyslexic children. Thirteen children with dyslexia, 13 non-dyslexic chronological age- and IQ-matched children and 13 non-dyslexic reading age- and IQ-matched children were examined. Test C of the DEM test was performed with and without eye movement recordings (eye tracker by SuriCog). The results of the three groups were compared. Children with dyslexia and non-dyslexic children of equivalent reading age have significant longer fixation time and take longer to read Test C of the DEM test than non-dyslexic children of similar chronological age. A significant correlation was also found between the fixation time and the number of words read in one minute with the total time to read Test C of the DEM test. DEM test is a useful test for exploring the oculomotor behavior of dyslexic children during reading. The maturation of cortical structures controlling fixation capability appears to play a crucial role in reading skills.

Interactions between eye movements and posture in children with neurodevelopmental disorders.

In everyday life, our activities frequently involve the simultaneous performance of two or more tasks. Sharing attention between two concurrent tasks may result in a decrease in performance specifically among children with neurodevelopmental disorders. The objective of the study was to determine whether the influence of postural conditions (sitting condition, single task; standing condition, dual task) on eye movement performances on three visual tasks with high attentional load (visually-guided saccade task, memory-guided saccade task and fixation task) was different in children with neurodevelopmental disorders (attention deficit and hyperactive disorder, dyslexia, and high functioning autism spectrum disorder) when compared to typically developing children. One hundred and four children (26 per group, sex-age- and IQ-matched groups) were evaluated. We found that for the fixation task only, the three groups of children with neurodevelopmental disorders had poorer eye movements performances in the standing condition compared to the sitting condition while no such difference was found for typically developing children. We suggest that children with neurodevelopmental disorders have fewer attentional resources available for performing correctly oculomotor tasks with high attentional load leading to impairment of these tasks for maintaining a good level of postural stability.

Effect of colored filters on reading capabilities in dyslexic children.

AIM: The aim of the present study was to examine the effects of colored filters on reading performance and eye movement control in children with and without dyslexia. METHODS: Eighteen children with dyslexia and 18 children without dyslexia were seated on a chair with their heads stabilized by a forehead and chin support. The children read different texts under the following three filter conditions: no filter, yellow filter, and green filter. The children's eye movements were recorded with a Mobile EyeBrain Tracker. Reading total time, duration of fixation between two successive saccades, pro-saccades amplitude and number of pro- and retro-saccades were obtained. RESULTS: Children with dyslexia read the fastest and had the shortest fixation time in the green filter condition compared with the other conditions. Furthermore, children with dyslexia showed the shortest fixation time in the green filter condition with respect to the other conditions. CONCLUSIONS: Taken together, these results suggested that the green filter improved reading performance in children with dyslexia because the filter most likely facilitated cortical activity and decreased visual distortions.

Eye movements and postural control in dyslexic children performing different visual tasks.

The aim of this study was to examine eye movements and postural control performance among dyslexic children while reading a text and performing the Landolt reading task. Fifteen dyslexic and 15 non-dyslexic children were asked to stand upright while performing two experimental visual tasks: text reading and Landolt reading. In the text reading task, children were asked to silently read a text displayed on a monitor, while in the Landolt reading task, the letters in the text were replaced by closed circles and Landolt rings, and children were asked to scan each circle/ring in a reading-like fashion, from left to right, and to count the number of Landolt rings. Eye movements (Mobile T2®, SuriCog) and center of pressure excursions (Framiral®, Grasse, France) were recorded. Visual performance variables were total reading time, mean duration of fixation, number of pro- and retro-saccades, and amplitude of pro-saccades. Postural performance variable was the center of pressure area. The results showed that dyslexic children spent more time reading the text and had a longer duration of fixation than non-dyslexic children. However, no difference was observed between dyslexic and non-dyslexic children in the Landolt reading task. Dyslexic children performed a higher number of pro- and retro-saccades than non-dyslexic children in both text reading and Landolt reading tasks. Dyslexic children had smaller pro-saccade amplitude than non-dyslexic children in the text reading task. Finally, postural performance was poorer in dyslexic children than in non-dyslexic children. Reading difficulties in dyslexic children are related to eye movement strategies required to scan and obtain lexical and semantic meaning. However, postural control performance, which was poor in dyslexic children, is not related to lexical and semantic reading requirements and might not also be related to different eye movement behavior.

Vertical disconjugacy during reading in dyslexic and non-dyslexic children.

PURPOSE: The objective of this study was to explore vertical binocular coordination in dyslexic and non-dyslexic children during saccades and post-saccadic fixation period while reading a text. METHODS: Binocular eye movements were recorded by an infrared system (Mobile T2®, SuriCog) in thirty-six dyslexic children from 7.3 to 13.6 years of age (mean age: 10.4 ±â€¯0.3 years) who were asked to silently read a four-line text during binocular viewing. Data were compared to those of thirty-six age-matched non-dyslexic children. RESULTS: Vertical disconjugacy during post-saccadic fixation was higher in dyslexic children with respect to non-dyslexic children group. Vertical disconjugacy was not age-dependent either for dyslexic children or for non-dyslexic children. CONCLUSIONS: The poor binocular vertical coordination observed in dyslexic children while reading could suggest a deficiency in the cerebellum and/or extra-ocular muscles involved in vertical eye alignment. Moreover, the fact that this vertical binocular coordination was not age-dependent could be due to an abnormal eye position and/or to a dysfunction of midbrain structures involved in vertical vergences.

Postural Control in Children with Dyslexia: Effects of Emotional Stimuli in a Dual-Task Environment.

The aim of this study was to compare the visual exploration strategies used during a postural control task across participants with and without dyslexia. We simultaneously recorded eye movements and postural control while children were viewing different types of emotional faces. Twenty-two children with dyslexia and twenty-two aged-matched children without dyslexia participated in the study. We analysed the surface area, the length and the mean velocity of the centre of pressure for balance in parallel with visual saccadic latency, the number of saccades and the time spent in regions of interest. Our results showed that postural stability in children with dyslexia was weaker and the surface area of their centre of pressure increased significantly when they viewed an unpleasant face. Moreover, children with dyslexia had different strategies to those used by children without dyslexia during visual exploration, and in particular when they viewed unpleasant emotional faces. We suggest that lower performance in emotional face processing in children with dyslexia could be due to a difference in their visual strategies, linked to their identification of unpleasant emotional faces. Copyright © 2017 John Wiley & Sons, Ltd.

Discriminant validity of spatial and temporal postural index in children with neurodevelopmental disorders.

Autism, learning disabilities and attention deficit/hyperactive disorder are often comorbid disorders. In order to try and find some markers that might be transnosographic, we hypothesized that abnormal postural sway profiles may discriminate children with neurodevelopmental disorders (NDDs) from typically developing children. The aim of our study was thus to compare spatial and temporal measures of the Center of Pressure in three distinct groups of children with NDDs (high functioning autism spectrum disorders, learning disabilities (dyslexia) and attention deficit/hyperactive disorders) and in typically developing children. Postural performances were thus evaluated in 92 children (23 per group, sex-, age- and IQ-matched groups) by using the Multitest Equilibre platform (Framiral®). Two viewing conditions (eyes open and eyes closed) were tested on a stable and unstable platform. Results reported similar poor postural instability for the three groups of children with NDDs with respect to the typically developing children, and this was observed for both spatial as well as temporal analysis of displacement of the center of pressure. Such postural instability observed in children with NDDs could be due to impairment in using sensorial inputs to eliminate body sway, probably due to poor cerebellar integration.

Influence of both cutaneous input from the foot soles and visual information on the control of postural stability in dyslexic children.

Dyslexic children show impaired in postural stability. The aim of our study was to test the influence of foot soles and visual information on the postural control of dyslexic children, compared to non-dyslexic children. Postural stability was evaluated with TechnoConcept® platform in twenty-four dyslexic children (mean age: 9.3±0.29years) and in twenty-four non-dyslexic children, gender- and age-matched, in two postural conditions (with and without foam: a 4-mm foam was put under their feet or not) and in two visual conditions (eyes open and eyes closed). We measured the surface area, the length and the mean velocity of the center of pressure (CoP). Moreover, we calculated the Romberg Quotient (RQ). Our results showed that the surface area, length and mean velocity of the CoP were significantly greater in the dyslexic children compared to the non-dyslexic children, particularly with foam and eyes closed. Furthermore, the RQ was significantly smaller in the dyslexic children and significantly greater without foam than with foam. All these findings suggest that dyslexic children are not able to compensate with other available inputs when sensorial inputs are less informative (with foam, or eyes closed), which results in poor postural stability. We suggest that the impairment of the cerebellar integration of all the sensorial inputs is responsible for the postural deficits observed in dyslexic children.

Differences between Dyslexic and Non-Dyslexic Children in the Performance of Phonological Visual-Auditory Recognition Tasks: An Eye-Tracking Study.

The object of this study was to explore further phonological visual-auditory recognition tasks in a group of fifty-six healthy children (mean age: 9.9 ± 0.3) and to compare these data to those recorded in twenty-six age-matched dyslexic children (mean age: 9.8 ± 0.2). Eye movements from both eyes were recorded using an infrared video-oculography system (MobileEBT® e(y)e BRAIN). The recognition task was performed under four conditions in which the target object was displayed either with phonologically unrelated objects (baseline condition), or with cohort or rhyme objects (cohort and rhyme conditions, respectively), or both together (rhyme + cohort condition). The percentage of the total time spent on the targets and the latency of the first saccade on the target were measured. Results in healthy children showed that the percentage of the total time spent in the baseline condition was significantly longer than in the other conditions, and that the latency of the first saccade in the cohort condition was significantly longer than in the other conditions; interestingly, the latency decreased significantly with the increasing age of the children. The developmental trend of phonological awareness was also observed in healthy children only. In contrast, we observed that for dyslexic children the total time spent on the target was similar in all four conditions tested, and also that they had similar latency values in both cohort and rhyme conditions. These findings suggest a different sensitivity to the phonological competitors between dyslexic and non-dyslexic children. Also, the eye-tracking technique provides online information about phonological awareness capabilities in children.

Immaturity of Visual Fixations in Dyslexic Children.

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.

The Effect of Training on Postural Control in Dyslexic Children.

The aim of this study was to explore whether a short postural training period could affect postural stability in dyslexic children. Postural performances were evaluated using Multitest Equilibre from Framiral. Posture was recorded in three different viewing conditions (eyes open fixating a target, eyes closed and eyes open with perturbed vision) and in two different postural conditions (on stable and unstable support). Two groups of dyslexic children participated in the study, i.e. G1: 16 dyslexic participants (mean age 9.9 ± 0.3 years) who performed short postural training and G2: 16 dyslexic participants of similar ages (mean age 9.1 ± 0.3 years) who did not perform any short postural training. Findings showed that short postural training improved postural stability on unstable support surfaces with perturbed vision: indeed the surface, the mean velocity of CoP and the spectral power indices in both directions decreased significantly, and the cancelling time in the antero-posterior direction improved significantly. Such improvement could be due to brain plasticity, which allows better performance in sensory process and cerebellar integration.

Spatial and temporal analysis of postural control in dyslexic children.

OBJECTIVE: The aim of this study is to examine postural control of dyslexic children using both spatial and temporal analysis. METHODS: Thirty dyslexic (mean age 9.7±0.3years) and thirty non-dyslexic age-matched children participated in the study. Postural stability was evaluated using Multitest Equilibre from Framiral®. Posture was recorded in the following conditions: eyes open fixating a target (EO) and eyes closed (EC) on stable (-S-) and unstable (-U-) platforms. RESULTS: The findings of this study showed poor postural stability in dyslexic children with respect to the non-dyslexic children group, as demonstrated by both spatial and temporal analysis. In both groups of children postural control depends on the condition, and improves when the eyes are open on a stable platform. Dyslexic children have spectral power indices that are higher than in non-dyslexic children and they showed a shorter cancelling time. CONCLUSION: Poor postural control in dyslexic children could be due to a deficit in using sensory information most likely caused by impairment in cerebellar activity. SIGNIFICANCE: The reliability of brain activation patterns, namely in using sensory input and cerebellar activity may explain the deficit in postural control in dyslexic children.

The influence of oculomotor tasks on postural control in dyslexic children.

Dual task is known to affect postural stability in children. We explored the effect of visual tasks on postural control in thirty dyslexic children. A selected group of thirty chronological age-matched non-dyslexic children (mean age: 9.92 ± 0.35 years) and a group of thirty reading age-matched non-dyslexic children (mean reading age: 7.90 ± 0.25 years) were chosen for comparison. All children underwent ophthalmologic and optometric evaluation. Eye movements were recorded by a video-oculography system (EyeBrain® T2) and postural sway was recorded simultaneously by a force platform (TechnoConept®). All children performed fixations, pursuits, pro- and anti-saccades tasks. Dyslexic children showed significantly poor near fusional vergence ranges (convergence and divergence) with respect to the non-dyslexic children groups. During the postural task, quality of fixation and anti-saccade performance in dyslexic children were significantly worse compared to the two non-dyslexic children groups. In contrast, the number of catch-up saccades during pursuits and the latency of pro- and anti-saccades were similar in the three groups of children examined. Concerning postural quality, dyslexic children were more unstable than chronological age-matched non-dyslexic children group. For all three groups of children tested we also observed that executing saccades (pro- and anti-saccades) reduced postural values significantly in comparison with fixation and pursuit tasks. The impairment in convergence and divergence fusional capabilities could be due to an immaturity in cortical structures controlling the vergence system. The poor oculomotor performance reported in dyslexic children suggested a deficit in allocating visual attention and their postural instability observed is in line with the cerebellar impairment previously reported in dyslexic children. Finally, pro- or anti-saccades reduce postural values compared to fixation and pursuit tasks in all groups of children tested, suggesting a different influence of visual tasks on postural control according to their attentional demand.

Binocular saccade coordination in reading and visual search: a developmental study in typical reader and dyslexic children.

Studies dealing with developmental aspects of binocular eye movement behavior during reading are scarce. In this study we have explored binocular strategies during reading and visual search tasks in a large population of dyslexic and typical readers. Binocular eye movements were recorded using a video-oculography system in 43 dyslexic children (aged 8-13) and in a group of 42 age-matched typical readers. The main findings are: (i) ocular motor characteristics of dyslexic children are impaired in comparison to those reported in typical children in reading task; (ii) a developmental effect exists in reading in control children, in dyslexic children the effect of development was observed only on fixation durations; and (iii) ocular motor behavior in the visual search tasks is similar for dyslexic children and for typical readers, except for the disconjugacy during and after the saccade: dyslexic children are impaired in comparison to typical children. Data reported here confirms and expands previous studies on children's reading. Both reading skills and binocular saccades coordination improve with age in typical readers. The atypical eye movement's patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an impairment of the ocular motor saccade and vergence systems interaction.